summaryrefslogtreecommitdiff
path: root/doc/coreutils.texi
blob: b85404b5c3acc1dde5562a0fdab4d92285ff9e47 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
4342
4343
4344
4345
4346
4347
4348
4349
4350
4351
4352
4353
4354
4355
4356
4357
4358
4359
4360
4361
4362
4363
4364
4365
4366
4367
4368
4369
4370
4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387
4388
4389
4390
4391
4392
4393
4394
4395
4396
4397
4398
4399
4400
4401
4402
4403
4404
4405
4406
4407
4408
4409
4410
4411
4412
4413
4414
4415
4416
4417
4418
4419
4420
4421
4422
4423
4424
4425
4426
4427
4428
4429
4430
4431
4432
4433
4434
4435
4436
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
4544
4545
4546
4547
4548
4549
4550
4551
4552
4553
4554
4555
4556
4557
4558
4559
4560
4561
4562
4563
4564
4565
4566
4567
4568
4569
4570
4571
4572
4573
4574
4575
4576
4577
4578
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
4595
4596
4597
4598
4599
4600
4601
4602
4603
4604
4605
4606
4607
4608
4609
4610
4611
4612
4613
4614
4615
4616
4617
4618
4619
4620
4621
4622
4623
4624
4625
4626
4627
4628
4629
4630
4631
4632
4633
4634
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
4646
4647
4648
4649
4650
4651
4652
4653
4654
4655
4656
4657
4658
4659
4660
4661
4662
4663
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
4677
4678
4679
4680
4681
4682
4683
4684
4685
4686
4687
4688
4689
4690
4691
4692
4693
4694
4695
4696
4697
4698
4699
4700
4701
4702
4703
4704
4705
4706
4707
4708
4709
4710
4711
4712
4713
4714
4715
4716
4717
4718
4719
4720
4721
4722
4723
4724
4725
4726
4727
4728
4729
4730
4731
4732
4733
4734
4735
4736
4737
4738
4739
4740
4741
4742
4743
4744
4745
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757
4758
4759
4760
4761
4762
4763
4764
4765
4766
4767
4768
4769
4770
4771
4772
4773
4774
4775
4776
4777
4778
4779
4780
4781
4782
4783
4784
4785
4786
4787
4788
4789
4790
4791
4792
4793
4794
4795
4796
4797
4798
4799
4800
4801
4802
4803
4804
4805
4806
4807
4808
4809
4810
4811
4812
4813
4814
4815
4816
4817
4818
4819
4820
4821
4822
4823
4824
4825
4826
4827
4828
4829
4830
4831
4832
4833
4834
4835
4836
4837
4838
4839
4840
4841
4842
4843
4844
4845
4846
4847
4848
4849
4850
4851
4852
4853
4854
4855
4856
4857
4858
4859
4860
4861
4862
4863
4864
4865
4866
4867
4868
4869
4870
4871
4872
4873
4874
4875
4876
4877
4878
4879
4880
4881
4882
4883
4884
4885
4886
4887
4888
4889
4890
4891
4892
4893
4894
4895
4896
4897
4898
4899
4900
4901
4902
4903
4904
4905
4906
4907
4908
4909
4910
4911
4912
4913
4914
4915
4916
4917
4918
4919
4920
4921
4922
4923
4924
4925
4926
4927
4928
4929
4930
4931
4932
4933
4934
4935
4936
4937
4938
4939
4940
4941
4942
4943
4944
4945
4946
4947
4948
4949
4950
4951
4952
4953
4954
4955
4956
4957
4958
4959
4960
4961
4962
4963
4964
4965
4966
4967
4968
4969
4970
4971
4972
4973
4974
4975
4976
4977
4978
4979
4980
4981
4982
4983
4984
4985
4986
4987
4988
4989
4990
4991
4992
4993
4994
4995
4996
4997
4998
4999
5000
5001
5002
5003
5004
5005
5006
5007
5008
5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020
5021
5022
5023
5024
5025
5026
5027
5028
5029
5030
5031
5032
5033
5034
5035
5036
5037
5038
5039
5040
5041
5042
5043
5044
5045
5046
5047
5048
5049
5050
5051
5052
5053
5054
5055
5056
5057
5058
5059
5060
5061
5062
5063
5064
5065
5066
5067
5068
5069
5070
5071
5072
5073
5074
5075
5076
5077
5078
5079
5080
5081
5082
5083
5084
5085
5086
5087
5088
5089
5090
5091
5092
5093
5094
5095
5096
5097
5098
5099
5100
5101
5102
5103
5104
5105
5106
5107
5108
5109
5110
5111
5112
5113
5114
5115
5116
5117
5118
5119
5120
5121
5122
5123
5124
5125
5126
5127
5128
5129
5130
5131
5132
5133
5134
5135
5136
5137
5138
5139
5140
5141
5142
5143
5144
5145
5146
5147
5148
5149
5150
5151
5152
5153
5154
5155
5156
5157
5158
5159
5160
5161
5162
5163
5164
5165
5166
5167
5168
5169
5170
5171
5172
5173
5174
5175
5176
5177
5178
5179
5180
5181
5182
5183
5184
5185
5186
5187
5188
5189
5190
5191
5192
5193
5194
5195
5196
5197
5198
5199
5200
5201
5202
5203
5204
5205
5206
5207
5208
5209
5210
5211
5212
5213
5214
5215
5216
5217
5218
5219
5220
5221
5222
5223
5224
5225
5226
5227
5228
5229
5230
5231
5232
5233
5234
5235
5236
5237
5238
5239
5240
5241
5242
5243
5244
5245
5246
5247
5248
5249
5250
5251
5252
5253
5254
5255
5256
5257
5258
5259
5260
5261
5262
5263
5264
5265
5266
5267
5268
5269
5270
5271
5272
5273
5274
5275
5276
5277
5278
5279
5280
5281
5282
5283
5284
5285
5286
5287
5288
5289
5290
5291
5292
5293
5294
5295
5296
5297
5298
5299
5300
5301
5302
5303
5304
5305
5306
5307
5308
5309
5310
5311
5312
5313
5314
5315
5316
5317
5318
5319
5320
5321
5322
5323
5324
5325
5326
5327
5328
5329
5330
5331
5332
5333
5334
5335
5336
5337
5338
5339
5340
5341
5342
5343
5344
5345
5346
5347
5348
5349
5350
5351
5352
5353
5354
5355
5356
5357
5358
5359
5360
5361
5362
5363
5364
5365
5366
5367
5368
5369
5370
5371
5372
5373
5374
5375
5376
5377
5378
5379
5380
5381
5382
5383
5384
5385
5386
5387
5388
5389
5390
5391
5392
5393
5394
5395
5396
5397
5398
5399
5400
5401
5402
5403
5404
5405
5406
5407
5408
5409
5410
5411
5412
5413
5414
5415
5416
5417
5418
5419
5420
5421
5422
5423
5424
5425
5426
5427
5428
5429
5430
5431
5432
5433
5434
5435
5436
5437
5438
5439
5440
5441
5442
5443
5444
5445
5446
5447
5448
5449
5450
5451
5452
5453
5454
5455
5456
5457
5458
5459
5460
5461
5462
5463
5464
5465
5466
5467
5468
5469
5470
5471
5472
5473
5474
5475
5476
5477
5478
5479
5480
5481
5482
5483
5484
5485
5486
5487
5488
5489
5490
5491
5492
5493
5494
5495
5496
5497
5498
5499
5500
5501
5502
5503
5504
5505
5506
5507
5508
5509
5510
5511
5512
5513
5514
5515
5516
5517
5518
5519
5520
5521
5522
5523
5524
5525
5526
5527
5528
5529
5530
5531
5532
5533
5534
5535
5536
5537
5538
5539
5540
5541
5542
5543
5544
5545
5546
5547
5548
5549
5550
5551
5552
5553
5554
5555
5556
5557
5558
5559
5560
5561
5562
5563
5564
5565
5566
5567
5568
5569
5570
5571
5572
5573
5574
5575
5576
5577
5578
5579
5580
5581
5582
5583
5584
5585
5586
5587
5588
5589
5590
5591
5592
5593
5594
5595
5596
5597
5598
5599
5600
5601
5602
5603
5604
5605
5606
5607
5608
5609
5610
5611
5612
5613
5614
5615
5616
5617
5618
5619
5620
5621
5622
5623
5624
5625
5626
5627
5628
5629
5630
5631
5632
5633
5634
5635
5636
5637
5638
5639
5640
5641
5642
5643
5644
5645
5646
5647
5648
5649
5650
5651
5652
5653
5654
5655
5656
5657
5658
5659
5660
5661
5662
5663
5664
5665
5666
5667
5668
5669
5670
5671
5672
5673
5674
5675
5676
5677
5678
5679
5680
5681
5682
5683
5684
5685
5686
5687
5688
5689
5690
5691
5692
5693
5694
5695
5696
5697
5698
5699
5700
5701
5702
5703
5704
5705
5706
5707
5708
5709
5710
5711
5712
5713
5714
5715
5716
5717
5718
5719
5720
5721
5722
5723
5724
5725
5726
5727
5728
5729
5730
5731
5732
5733
5734
5735
5736
5737
5738
5739
5740
5741
5742
5743
5744
5745
5746
5747
5748
5749
5750
5751
5752
5753
5754
5755
5756
5757
5758
5759
5760
5761
5762
5763
5764
5765
5766
5767
5768
5769
5770
5771
5772
5773
5774
5775
5776
5777
5778
5779
5780
5781
5782
5783
5784
5785
5786
5787
5788
5789
5790
5791
5792
5793
5794
5795
5796
5797
5798
5799
5800
5801
5802
5803
5804
5805
5806
5807
5808
5809
5810
5811
5812
5813
5814
5815
5816
5817
5818
5819
5820
5821
5822
5823
5824
5825
5826
5827
5828
5829
5830
5831
5832
5833
5834
5835
5836
5837
5838
5839
5840
5841
5842
5843
5844
5845
5846
5847
5848
5849
5850
5851
5852
5853
5854
5855
5856
5857
5858
5859
5860
5861
5862
5863
5864
5865
5866
5867
5868
5869
5870
5871
5872
5873
5874
5875
5876
5877
5878
5879
5880
5881
5882
5883
5884
5885
5886
5887
5888
5889
5890
5891
5892
5893
5894
5895
5896
5897
5898
5899
5900
5901
5902
5903
5904
5905
5906
5907
5908
5909
5910
5911
5912
5913
5914
5915
5916
5917
5918
5919
5920
5921
5922
5923
5924
5925
5926
5927
5928
5929
5930
5931
5932
5933
5934
5935
5936
5937
5938
5939
5940
5941
5942
5943
5944
5945
5946
5947
5948
5949
5950
5951
5952
5953
5954
5955
5956
5957
5958
5959
5960
5961
5962
5963
5964
5965
5966
5967
5968
5969
5970
5971
5972
5973
5974
5975
5976
5977
5978
5979
5980
5981
5982
5983
5984
5985
5986
5987
5988
5989
5990
5991
5992
5993
5994
5995
5996
5997
5998
5999
6000
6001
6002
6003
6004
6005
6006
6007
6008
6009
6010
6011
6012
6013
6014
6015
6016
6017
6018
6019
6020
6021
6022
6023
6024
6025
6026
6027
6028
6029
6030
6031
6032
6033
6034
6035
6036
6037
6038
6039
6040
6041
6042
6043
6044
6045
6046
6047
6048
6049
6050
6051
6052
6053
6054
6055
6056
6057
6058
6059
6060
6061
6062
6063
6064
6065
6066
6067
6068
6069
6070
6071
6072
6073
6074
6075
6076
6077
6078
6079
6080
6081
6082
6083
6084
6085
6086
6087
6088
6089
6090
6091
6092
6093
6094
6095
6096
6097
6098
6099
6100
6101
6102
6103
6104
6105
6106
6107
6108
6109
6110
6111
6112
6113
6114
6115
6116
6117
6118
6119
6120
6121
6122
6123
6124
6125
6126
6127
6128
6129
6130
6131
6132
6133
6134
6135
6136
6137
6138
6139
6140
6141
6142
6143
6144
6145
6146
6147
6148
6149
6150
6151
6152
6153
6154
6155
6156
6157
6158
6159
6160
6161
6162
6163
6164
6165
6166
6167
6168
6169
6170
6171
6172
6173
6174
6175
6176
6177
6178
6179
6180
6181
6182
6183
6184
6185
6186
6187
6188
6189
6190
6191
6192
6193
6194
6195
6196
6197
6198
6199
6200
6201
6202
6203
6204
6205
6206
6207
6208
6209
6210
6211
6212
6213
6214
6215
6216
6217
6218
6219
6220
6221
6222
6223
6224
6225
6226
6227
6228
6229
6230
6231
6232
6233
6234
6235
6236
6237
6238
6239
6240
6241
6242
6243
6244
6245
6246
6247
6248
6249
6250
6251
6252
6253
6254
6255
6256
6257
6258
6259
6260
6261
6262
6263
6264
6265
6266
6267
6268
6269
6270
6271
6272
6273
6274
6275
6276
6277
6278
6279
6280
6281
6282
6283
6284
6285
6286
6287
6288
6289
6290
6291
6292
6293
6294
6295
6296
6297
6298
6299
6300
6301
6302
6303
6304
6305
6306
6307
6308
6309
6310
6311
6312
6313
6314
6315
6316
6317
6318
6319
6320
6321
6322
6323
6324
6325
6326
6327
6328
6329
6330
6331
6332
6333
6334
6335
6336
6337
6338
6339
6340
6341
6342
6343
6344
6345
6346
6347
6348
6349
6350
6351
6352
6353
6354
6355
6356
6357
6358
6359
6360
6361
6362
6363
6364
6365
6366
6367
6368
6369
6370
6371
6372
6373
6374
6375
6376
6377
6378
6379
6380
6381
6382
6383
6384
6385
6386
6387
6388
6389
6390
6391
6392
6393
6394
6395
6396
6397
6398
6399
6400
6401
6402
6403
6404
6405
6406
6407
6408
6409
6410
6411
6412
6413
6414
6415
6416
6417
6418
6419
6420
6421
6422
6423
6424
6425
6426
6427
6428
6429
6430
6431
6432
6433
6434
6435
6436
6437
6438
6439
6440
6441
6442
6443
6444
6445
6446
6447
6448
6449
6450
6451
6452
6453
6454
6455
6456
6457
6458
6459
6460
6461
6462
6463
6464
6465
6466
6467
6468
6469
6470
6471
6472
6473
6474
6475
6476
6477
6478
6479
6480
6481
6482
6483
6484
6485
6486
6487
6488
6489
6490
6491
6492
6493
6494
6495
6496
6497
6498
6499
6500
6501
6502
6503
6504
6505
6506
6507
6508
6509
6510
6511
6512
6513
6514
6515
6516
6517
6518
6519
6520
6521
6522
6523
6524
6525
6526
6527
6528
6529
6530
6531
6532
6533
6534
6535
6536
6537
6538
6539
6540
6541
6542
6543
6544
6545
6546
6547
6548
6549
6550
6551
6552
6553
6554
6555
6556
6557
6558
6559
6560
6561
6562
6563
6564
6565
6566
6567
6568
6569
6570
6571
6572
6573
6574
6575
6576
6577
6578
6579
6580
6581
6582
6583
6584
6585
6586
6587
6588
6589
6590
6591
6592
6593
6594
6595
6596
6597
6598
6599
6600
6601
6602
6603
6604
6605
6606
6607
6608
6609
6610
6611
6612
6613
6614
6615
6616
6617
6618
6619
6620
6621
6622
6623
6624
6625
6626
6627
6628
6629
6630
6631
6632
6633
6634
6635
6636
6637
6638
6639
6640
6641
6642
6643
6644
6645
6646
6647
6648
6649
6650
6651
6652
6653
6654
6655
6656
6657
6658
6659
6660
6661
6662
6663
6664
6665
6666
6667
6668
6669
6670
6671
6672
6673
6674
6675
6676
6677
6678
6679
6680
6681
6682
6683
6684
6685
6686
6687
6688
6689
6690
6691
6692
6693
6694
6695
6696
6697
6698
6699
6700
6701
6702
6703
6704
6705
6706
6707
6708
6709
6710
6711
6712
6713
6714
6715
6716
6717
6718
6719
6720
6721
6722
6723
6724
6725
6726
6727
6728
6729
6730
6731
6732
6733
6734
6735
6736
6737
6738
6739
6740
6741
6742
6743
6744
6745
6746
6747
6748
6749
6750
6751
6752
6753
6754
6755
6756
6757
6758
6759
6760
6761
6762
6763
6764
6765
6766
6767
6768
6769
6770
6771
6772
6773
6774
6775
6776
6777
6778
6779
6780
6781
6782
6783
6784
6785
6786
6787
6788
6789
6790
6791
6792
6793
6794
6795
6796
6797
6798
6799
6800
6801
6802
6803
6804
6805
6806
6807
6808
6809
6810
6811
6812
6813
6814
6815
6816
6817
6818
6819
6820
6821
6822
6823
6824
6825
6826
6827
6828
6829
6830
6831
6832
6833
6834
6835
6836
6837
6838
6839
6840
6841
6842
6843
6844
6845
6846
6847
6848
6849
6850
6851
6852
6853
6854
6855
6856
6857
6858
6859
6860
6861
6862
6863
6864
6865
6866
6867
6868
6869
6870
6871
6872
6873
6874
6875
6876
6877
6878
6879
6880
6881
6882
6883
6884
6885
6886
6887
6888
6889
6890
6891
6892
6893
6894
6895
6896
6897
6898
6899
6900
6901
6902
6903
6904
6905
6906
6907
6908
6909
6910
6911
6912
6913
6914
6915
6916
6917
6918
6919
6920
6921
6922
6923
6924
6925
6926
6927
6928
6929
6930
6931
6932
6933
6934
6935
6936
6937
6938
6939
6940
6941
6942
6943
6944
6945
6946
6947
6948
6949
6950
6951
6952
6953
6954
6955
6956
6957
6958
6959
6960
6961
6962
6963
6964
6965
6966
6967
6968
6969
6970
6971
6972
6973
6974
6975
6976
6977
6978
6979
6980
6981
6982
6983
6984
6985
6986
6987
6988
6989
6990
6991
6992
6993
6994
6995
6996
6997
6998
6999
7000
7001
7002
7003
7004
7005
7006
7007
7008
7009
7010
7011
7012
7013
7014
7015
7016
7017
7018
7019
7020
7021
7022
7023
7024
7025
7026
7027
7028
7029
7030
7031
7032
7033
7034
7035
7036
7037
7038
7039
7040
7041
7042
7043
7044
7045
7046
7047
7048
7049
7050
7051
7052
7053
7054
7055
7056
7057
7058
7059
7060
7061
7062
7063
7064
7065
7066
7067
7068
7069
7070
7071
7072
7073
7074
7075
7076
7077
7078
7079
7080
7081
7082
7083
7084
7085
7086
7087
7088
7089
7090
7091
7092
7093
7094
7095
7096
7097
7098
7099
7100
7101
7102
7103
7104
7105
7106
7107
7108
7109
7110
7111
7112
7113
7114
7115
7116
7117
7118
7119
7120
7121
7122
7123
7124
7125
7126
7127
7128
7129
7130
7131
7132
7133
7134
7135
7136
7137
7138
7139
7140
7141
7142
7143
7144
7145
7146
7147
7148
7149
7150
7151
7152
7153
7154
7155
7156
7157
7158
7159
7160
7161
7162
7163
7164
7165
7166
7167
7168
7169
7170
7171
7172
7173
7174
7175
7176
7177
7178
7179
7180
7181
7182
7183
7184
7185
7186
7187
7188
7189
7190
7191
7192
7193
7194
7195
7196
7197
7198
7199
7200
7201
7202
7203
7204
7205
7206
7207
7208
7209
7210
7211
7212
7213
7214
7215
7216
7217
7218
7219
7220
7221
7222
7223
7224
7225
7226
7227
7228
7229
7230
7231
7232
7233
7234
7235
7236
7237
7238
7239
7240
7241
7242
7243
7244
7245
7246
7247
7248
7249
7250
7251
7252
7253
7254
7255
7256
7257
7258
7259
7260
7261
7262
7263
7264
7265
7266
7267
7268
7269
7270
7271
7272
7273
7274
7275
7276
7277
7278
7279
7280
7281
7282
7283
7284
7285
7286
7287
7288
7289
7290
7291
7292
7293
7294
7295
7296
7297
7298
7299
7300
7301
7302
7303
7304
7305
7306
7307
7308
7309
7310
7311
7312
7313
7314
7315
7316
7317
7318
7319
7320
7321
7322
7323
7324
7325
7326
7327
7328
7329
7330
7331
7332
7333
7334
7335
7336
7337
7338
7339
7340
7341
7342
7343
7344
7345
7346
7347
7348
7349
7350
7351
7352
7353
7354
7355
7356
7357
7358
7359
7360
7361
7362
7363
7364
7365
7366
7367
7368
7369
7370
7371
7372
7373
7374
7375
7376
7377
7378
7379
7380
7381
7382
7383
7384
7385
7386
7387
7388
7389
7390
7391
7392
7393
7394
7395
7396
7397
7398
7399
7400
7401
7402
7403
7404
7405
7406
7407
7408
7409
7410
7411
7412
7413
7414
7415
7416
7417
7418
7419
7420
7421
7422
7423
7424
7425
7426
7427
7428
7429
7430
7431
7432
7433
7434
7435
7436
7437
7438
7439
7440
7441
7442
7443
7444
7445
7446
7447
7448
7449
7450
7451
7452
7453
7454
7455
7456
7457
7458
7459
7460
7461
7462
7463
7464
7465
7466
7467
7468
7469
7470
7471
7472
7473
7474
7475
7476
7477
7478
7479
7480
7481
7482
7483
7484
7485
7486
7487
7488
7489
7490
7491
7492
7493
7494
7495
7496
7497
7498
7499
7500
7501
7502
7503
7504
7505
7506
7507
7508
7509
7510
7511
7512
7513
7514
7515
7516
7517
7518
7519
7520
7521
7522
7523
7524
7525
7526
7527
7528
7529
7530
7531
7532
7533
7534
7535
7536
7537
7538
7539
7540
7541
7542
7543
7544
7545
7546
7547
7548
7549
7550
7551
7552
7553
7554
7555
7556
7557
7558
7559
7560
7561
7562
7563
7564
7565
7566
7567
7568
7569
7570
7571
7572
7573
7574
7575
7576
7577
7578
7579
7580
7581
7582
7583
7584
7585
7586
7587
7588
7589
7590
7591
7592
7593
7594
7595
7596
7597
7598
7599
7600
7601
7602
7603
7604
7605
7606
7607
7608
7609
7610
7611
7612
7613
7614
7615
7616
7617
7618
7619
7620
7621
7622
7623
7624
7625
7626
7627
7628
7629
7630
7631
7632
7633
7634
7635
7636
7637
7638
7639
7640
7641
7642
7643
7644
7645
7646
7647
7648
7649
7650
7651
7652
7653
7654
7655
7656
7657
7658
7659
7660
7661
7662
7663
7664
7665
7666
7667
7668
7669
7670
7671
7672
7673
7674
7675
7676
7677
7678
7679
7680
7681
7682
7683
7684
7685
7686
7687
7688
7689
7690
7691
7692
7693
7694
7695
7696
7697
7698
7699
7700
7701
7702
7703
7704
7705
7706
7707
7708
7709
7710
7711
7712
7713
7714
7715
7716
7717
7718
7719
7720
7721
7722
7723
7724
7725
7726
7727
7728
7729
7730
7731
7732
7733
7734
7735
7736
7737
7738
7739
7740
7741
7742
7743
7744
7745
7746
7747
7748
7749
7750
7751
7752
7753
7754
7755
7756
7757
7758
7759
7760
7761
7762
7763
7764
7765
7766
7767
7768
7769
7770
7771
7772
7773
7774
7775
7776
7777
7778
7779
7780
7781
7782
7783
7784
7785
7786
7787
7788
7789
7790
7791
7792
7793
7794
7795
7796
7797
7798
7799
7800
7801
7802
7803
7804
7805
7806
7807
7808
7809
7810
7811
7812
7813
7814
7815
7816
7817
7818
7819
7820
7821
7822
7823
7824
7825
7826
7827
7828
7829
7830
7831
7832
7833
7834
7835
7836
7837
7838
7839
7840
7841
7842
7843
7844
7845
7846
7847
7848
7849
7850
7851
7852
7853
7854
7855
7856
7857
7858
7859
7860
7861
7862
7863
7864
7865
7866
7867
7868
7869
7870
7871
7872
7873
7874
7875
7876
7877
7878
7879
7880
7881
7882
7883
7884
7885
7886
7887
7888
7889
7890
7891
7892
7893
7894
7895
7896
7897
7898
7899
7900
7901
7902
7903
7904
7905
7906
7907
7908
7909
7910
7911
7912
7913
7914
7915
7916
7917
7918
7919
7920
7921
7922
7923
7924
7925
7926
7927
7928
7929
7930
7931
7932
7933
7934
7935
7936
7937
7938
7939
7940
7941
7942
7943
7944
7945
7946
7947
7948
7949
7950
7951
7952
7953
7954
7955
7956
7957
7958
7959
7960
7961
7962
7963
7964
7965
7966
7967
7968
7969
7970
7971
7972
7973
7974
7975
7976
7977
7978
7979
7980
7981
7982
7983
7984
7985
7986
7987
7988
7989
7990
7991
7992
7993
7994
7995
7996
7997
7998
7999
8000
8001
8002
8003
8004
8005
8006
8007
8008
8009
8010
8011
8012
8013
8014
8015
8016
8017
8018
8019
8020
8021
8022
8023
8024
8025
8026
8027
8028
8029
8030
8031
8032
8033
8034
8035
8036
8037
8038
8039
8040
8041
8042
8043
8044
8045
8046
8047
8048
8049
8050
8051
8052
8053
8054
8055
8056
8057
8058
8059
8060
8061
8062
8063
8064
8065
8066
8067
8068
8069
8070
8071
8072
8073
8074
8075
8076
8077
8078
8079
8080
8081
8082
8083
8084
8085
8086
8087
8088
8089
8090
8091
8092
8093
8094
8095
8096
8097
8098
8099
8100
8101
8102
8103
8104
8105
8106
8107
8108
8109
8110
8111
8112
8113
8114
8115
8116
8117
8118
8119
8120
8121
8122
8123
8124
8125
8126
8127
8128
8129
8130
8131
8132
8133
8134
8135
8136
8137
8138
8139
8140
8141
8142
8143
8144
8145
8146
8147
8148
8149
8150
8151
8152
8153
8154
8155
8156
8157
8158
8159
8160
8161
8162
8163
8164
8165
8166
8167
8168
8169
8170
8171
8172
8173
8174
8175
8176
8177
8178
8179
8180
8181
8182
8183
8184
8185
8186
8187
8188
8189
8190
8191
8192
8193
8194
8195
8196
8197
8198
8199
8200
8201
8202
8203
8204
8205
8206
8207
8208
8209
8210
8211
8212
8213
8214
8215
8216
8217
8218
8219
8220
8221
8222
8223
8224
8225
8226
8227
8228
8229
8230
8231
8232
8233
8234
8235
8236
8237
8238
8239
8240
8241
8242
8243
8244
8245
8246
8247
8248
8249
8250
8251
8252
8253
8254
8255
8256
8257
8258
8259
8260
8261
8262
8263
8264
8265
8266
8267
8268
8269
8270
8271
8272
8273
8274
8275
8276
8277
8278
8279
8280
8281
8282
8283
8284
8285
8286
8287
8288
8289
8290
8291
8292
8293
8294
8295
8296
8297
8298
8299
8300
8301
8302
8303
8304
8305
8306
8307
8308
8309
8310
8311
8312
8313
8314
8315
8316
8317
8318
8319
8320
8321
8322
8323
8324
8325
8326
8327
8328
8329
8330
8331
8332
8333
8334
8335
8336
8337
8338
8339
8340
8341
8342
8343
8344
8345
8346
8347
8348
8349
8350
8351
8352
8353
8354
8355
8356
8357
8358
8359
8360
8361
8362
8363
8364
8365
8366
8367
8368
8369
8370
8371
8372
8373
8374
8375
8376
8377
8378
8379
8380
8381
8382
8383
8384
8385
8386
8387
8388
8389
8390
8391
8392
8393
8394
8395
8396
8397
8398
8399
8400
8401
8402
8403
8404
8405
8406
8407
8408
8409
8410
8411
8412
8413
8414
8415
8416
8417
8418
8419
8420
8421
8422
8423
8424
8425
8426
8427
8428
8429
8430
8431
8432
8433
8434
8435
8436
8437
8438
8439
8440
8441
8442
8443
8444
8445
8446
8447
8448
8449
8450
8451
8452
8453
8454
8455
8456
8457
8458
8459
8460
8461
8462
8463
8464
8465
8466
8467
8468
8469
8470
8471
8472
8473
8474
8475
8476
8477
8478
8479
8480
8481
8482
8483
8484
8485
8486
8487
8488
8489
8490
8491
8492
8493
8494
8495
8496
8497
8498
8499
8500
8501
8502
8503
8504
8505
8506
8507
8508
8509
8510
8511
8512
8513
8514
8515
8516
8517
8518
8519
8520
8521
8522
8523
8524
8525
8526
8527
8528
8529
8530
8531
8532
8533
8534
8535
8536
8537
8538
8539
8540
8541
8542
8543
8544
8545
8546
8547
8548
8549
8550
8551
8552
8553
8554
8555
8556
8557
8558
8559
8560
8561
8562
8563
8564
8565
8566
8567
8568
8569
8570
8571
8572
8573
8574
8575
8576
8577
8578
8579
8580
8581
8582
8583
8584
8585
8586
8587
8588
8589
8590
8591
8592
8593
8594
8595
8596
8597
8598
8599
8600
8601
8602
8603
8604
8605
8606
8607
8608
8609
8610
8611
8612
8613
8614
8615
8616
8617
8618
8619
8620
8621
8622
8623
8624
8625
8626
8627
8628
8629
8630
8631
8632
8633
8634
8635
8636
8637
8638
8639
8640
8641
8642
8643
8644
8645
8646
8647
8648
8649
8650
8651
8652
8653
8654
8655
8656
8657
8658
8659
8660
8661
8662
8663
8664
8665
8666
8667
8668
8669
8670
8671
8672
8673
8674
8675
8676
8677
8678
8679
8680
8681
8682
8683
8684
8685
8686
8687
8688
8689
8690
8691
8692
8693
8694
8695
8696
8697
8698
8699
8700
8701
8702
8703
8704
8705
8706
8707
8708
8709
8710
8711
8712
8713
8714
8715
8716
8717
8718
8719
8720
8721
8722
8723
8724
8725
8726
8727
8728
8729
8730
8731
8732
8733
8734
8735
8736
8737
8738
8739
8740
8741
8742
8743
8744
8745
8746
8747
8748
8749
8750
8751
8752
8753
8754
8755
8756
8757
8758
8759
8760
8761
8762
8763
8764
8765
8766
8767
8768
8769
8770
8771
8772
8773
8774
8775
8776
8777
8778
8779
8780
8781
8782
8783
8784
8785
8786
8787
8788
8789
8790
8791
8792
8793
8794
8795
8796
8797
8798
8799
8800
8801
8802
8803
8804
8805
8806
8807
8808
8809
8810
8811
8812
8813
8814
8815
8816
8817
8818
8819
8820
8821
8822
8823
8824
8825
8826
8827
8828
8829
8830
8831
8832
8833
8834
8835
8836
8837
8838
8839
8840
8841
8842
8843
8844
8845
8846
8847
8848
8849
8850
8851
8852
8853
8854
8855
8856
8857
8858
8859
8860
8861
8862
8863
8864
8865
8866
8867
8868
8869
8870
8871
8872
8873
8874
8875
8876
8877
8878
8879
8880
8881
8882
8883
8884
8885
8886
8887
8888
8889
8890
8891
8892
8893
8894
8895
8896
8897
8898
8899
8900
8901
8902
8903
8904
8905
8906
8907
8908
8909
8910
8911
8912
8913
8914
8915
8916
8917
8918
8919
8920
8921
8922
8923
8924
8925
8926
8927
8928
8929
8930
8931
8932
8933
8934
8935
8936
8937
8938
8939
8940
8941
8942
8943
8944
8945
8946
8947
8948
8949
8950
8951
8952
8953
8954
8955
8956
8957
8958
8959
8960
8961
8962
8963
8964
8965
8966
8967
8968
8969
8970
8971
8972
8973
8974
8975
8976
8977
8978
8979
8980
8981
8982
8983
8984
8985
8986
8987
8988
8989
8990
8991
8992
8993
8994
8995
8996
8997
8998
8999
9000
9001
9002
9003
9004
9005
9006
9007
9008
9009
9010
9011
9012
9013
9014
9015
9016
9017
9018
9019
9020
9021
9022
9023
9024
9025
9026
9027
9028
9029
9030
9031
9032
9033
9034
9035
9036
9037
9038
9039
9040
9041
9042
9043
9044
9045
9046
9047
9048
9049
9050
9051
9052
9053
9054
9055
9056
9057
9058
9059
9060
9061
9062
9063
9064
9065
9066
9067
9068
9069
9070
9071
9072
9073
9074
9075
9076
9077
9078
9079
9080
9081
9082
9083
9084
9085
9086
9087
9088
9089
9090
9091
9092
9093
9094
9095
9096
9097
9098
9099
9100
9101
9102
9103
9104
9105
9106
9107
9108
9109
9110
9111
9112
9113
9114
9115
9116
9117
9118
9119
9120
9121
9122
9123
9124
9125
9126
9127
9128
9129
9130
9131
9132
9133
9134
9135
9136
9137
9138
9139
9140
9141
9142
9143
9144
9145
9146
9147
9148
9149
9150
9151
9152
9153
9154
9155
9156
9157
9158
9159
9160
9161
9162
9163
9164
9165
9166
9167
9168
9169
9170
9171
9172
9173
9174
9175
9176
9177
9178
9179
9180
9181
9182
9183
9184
9185
9186
9187
9188
9189
9190
9191
9192
9193
9194
9195
9196
9197
9198
9199
9200
9201
9202
9203
9204
9205
9206
9207
9208
9209
9210
9211
9212
9213
9214
9215
9216
9217
9218
9219
9220
9221
9222
9223
9224
9225
9226
9227
9228
9229
9230
9231
9232
9233
9234
9235
9236
9237
9238
9239
9240
9241
9242
9243
9244
9245
9246
9247
9248
9249
9250
9251
9252
9253
9254
9255
9256
9257
9258
9259
9260
9261
9262
9263
9264
9265
9266
9267
9268
9269
9270
9271
9272
9273
9274
9275
9276
9277
9278
9279
9280
9281
9282
9283
9284
9285
9286
9287
9288
9289
9290
9291
9292
9293
9294
9295
9296
9297
9298
9299
9300
9301
9302
9303
9304
9305
9306
9307
9308
9309
9310
9311
9312
9313
9314
9315
9316
9317
9318
9319
9320
9321
9322
9323
9324
9325
9326
9327
9328
9329
9330
9331
9332
9333
9334
9335
9336
9337
9338
9339
9340
9341
9342
9343
9344
9345
9346
9347
9348
9349
9350
9351
9352
9353
9354
9355
9356
9357
9358
9359
9360
9361
9362
9363
9364
9365
9366
9367
9368
9369
9370
9371
9372
9373
9374
9375
9376
9377
9378
9379
9380
9381
9382
9383
9384
9385
9386
9387
9388
9389
9390
9391
9392
9393
9394
9395
9396
9397
9398
9399
9400
9401
9402
9403
9404
9405
9406
9407
9408
9409
9410
9411
9412
9413
9414
9415
9416
9417
9418
9419
9420
9421
9422
9423
9424
9425
9426
9427
9428
9429
9430
9431
9432
9433
9434
9435
9436
9437
9438
9439
9440
9441
9442
9443
9444
9445
9446
9447
9448
9449
9450
9451
9452
9453
9454
9455
9456
9457
9458
9459
9460
9461
9462
9463
9464
9465
9466
9467
9468
9469
9470
9471
9472
9473
9474
9475
9476
9477
9478
9479
9480
9481
9482
9483
9484
9485
9486
9487
9488
9489
9490
9491
9492
9493
9494
9495
9496
9497
9498
9499
9500
9501
9502
9503
9504
9505
9506
9507
9508
9509
9510
9511
9512
9513
9514
9515
9516
9517
9518
9519
9520
9521
9522
9523
9524
9525
9526
9527
9528
9529
9530
9531
9532
9533
9534
9535
9536
9537
9538
9539
9540
9541
9542
9543
9544
9545
9546
9547
9548
9549
9550
9551
9552
9553
9554
9555
9556
9557
9558
9559
9560
9561
9562
9563
9564
9565
9566
9567
9568
9569
9570
9571
9572
9573
9574
9575
9576
9577
9578
9579
9580
9581
9582
9583
9584
9585
9586
9587
9588
9589
9590
9591
9592
9593
9594
9595
9596
9597
9598
9599
9600
9601
9602
9603
9604
9605
9606
9607
9608
9609
9610
9611
9612
9613
9614
9615
9616
9617
9618
9619
9620
9621
9622
9623
9624
9625
9626
9627
9628
9629
9630
9631
9632
9633
9634
9635
9636
9637
9638
9639
9640
9641
9642
9643
9644
9645
9646
9647
9648
9649
9650
9651
9652
9653
9654
9655
9656
9657
9658
9659
9660
9661
9662
9663
9664
9665
9666
9667
9668
9669
9670
9671
9672
9673
9674
9675
9676
9677
9678
9679
9680
9681
9682
9683
9684
9685
9686
9687
9688
9689
9690
9691
9692
9693
9694
9695
9696
9697
9698
9699
9700
9701
9702
9703
9704
9705
9706
9707
9708
9709
9710
9711
9712
9713
9714
9715
9716
9717
9718
9719
9720
9721
9722
9723
9724
9725
9726
9727
9728
9729
9730
9731
9732
9733
9734
9735
9736
9737
9738
9739
9740
9741
9742
9743
9744
9745
9746
9747
9748
9749
9750
9751
9752
9753
9754
9755
9756
9757
9758
9759
9760
9761
9762
9763
9764
9765
9766
9767
9768
9769
9770
9771
9772
9773
9774
9775
9776
9777
9778
9779
9780
9781
9782
9783
9784
9785
9786
9787
9788
9789
9790
9791
9792
9793
9794
9795
9796
9797
9798
9799
9800
9801
9802
9803
9804
9805
9806
9807
9808
9809
9810
9811
9812
9813
9814
9815
9816
9817
9818
9819
9820
9821
9822
9823
9824
9825
9826
9827
9828
9829
9830
9831
9832
9833
9834
9835
9836
9837
9838
9839
9840
9841
9842
9843
9844
9845
9846
9847
9848
9849
9850
9851
9852
9853
9854
9855
9856
9857
9858
9859
9860
9861
9862
9863
9864
9865
9866
9867
9868
9869
9870
9871
9872
9873
9874
9875
9876
9877
9878
9879
9880
9881
9882
9883
9884
9885
9886
9887
9888
9889
9890
9891
9892
9893
9894
9895
9896
9897
9898
9899
9900
9901
9902
9903
9904
9905
9906
9907
9908
9909
9910
9911
9912
9913
9914
9915
9916
9917
9918
9919
9920
9921
9922
9923
9924
9925
9926
9927
9928
9929
9930
9931
9932
9933
9934
9935
9936
9937
9938
9939
9940
9941
9942
9943
9944
9945
9946
9947
9948
9949
9950
9951
9952
9953
9954
9955
9956
9957
9958
9959
9960
9961
9962
9963
9964
9965
9966
9967
9968
9969
9970
9971
9972
9973
9974
9975
9976
9977
9978
9979
9980
9981
9982
9983
9984
9985
9986
9987
9988
9989
9990
9991
9992
9993
9994
9995
9996
9997
9998
9999
10000
10001
10002
10003
10004
10005
10006
10007
10008
10009
10010
10011
10012
10013
10014
10015
10016
10017
10018
10019
10020
10021
10022
10023
10024
10025
10026
10027
10028
10029
10030
10031
10032
10033
10034
10035
10036
10037
10038
10039
10040
10041
10042
10043
10044
10045
10046
10047
10048
10049
10050
10051
10052
10053
10054
10055
10056
10057
10058
10059
10060
10061
10062
10063
10064
10065
10066
10067
10068
10069
10070
10071
10072
10073
10074
10075
10076
10077
10078
10079
10080
10081
10082
10083
10084
10085
10086
10087
10088
10089
10090
10091
10092
10093
10094
10095
10096
10097
10098
10099
10100
10101
10102
10103
10104
10105
10106
10107
10108
10109
10110
10111
10112
10113
10114
10115
10116
10117
10118
10119
10120
10121
10122
10123
10124
10125
10126
10127
10128
10129
10130
10131
10132
10133
10134
10135
10136
10137
10138
10139
10140
10141
10142
10143
10144
10145
10146
10147
10148
10149
10150
10151
10152
10153
10154
10155
10156
10157
10158
10159
10160
10161
10162
10163
10164
10165
10166
10167
10168
10169
10170
10171
10172
10173
10174
10175
10176
10177
10178
10179
10180
10181
10182
10183
10184
10185
10186
10187
10188
10189
10190
10191
10192
10193
10194
10195
10196
10197
10198
10199
10200
10201
10202
10203
10204
10205
10206
10207
10208
10209
10210
10211
10212
10213
10214
10215
10216
10217
10218
10219
10220
10221
10222
10223
10224
10225
10226
10227
10228
10229
10230
10231
10232
10233
10234
10235
10236
10237
10238
10239
10240
10241
10242
10243
10244
10245
10246
10247
10248
10249
10250
10251
10252
10253
10254
10255
10256
10257
10258
10259
10260
10261
10262
10263
10264
10265
10266
10267
10268
10269
10270
10271
10272
10273
10274
10275
10276
10277
10278
10279
10280
10281
10282
10283
10284
10285
10286
10287
10288
10289
10290
10291
10292
10293
10294
10295
10296
10297
10298
10299
10300
10301
10302
10303
10304
10305
10306
10307
10308
10309
10310
10311
10312
10313
10314
10315
10316
10317
10318
10319
10320
10321
10322
10323
10324
10325
10326
10327
10328
10329
10330
10331
10332
10333
10334
10335
10336
10337
10338
10339
10340
10341
10342
10343
10344
10345
10346
10347
10348
10349
10350
10351
10352
10353
10354
10355
10356
10357
10358
10359
10360
10361
10362
10363
10364
10365
10366
10367
10368
10369
10370
10371
10372
10373
10374
10375
10376
10377
10378
10379
10380
10381
10382
10383
10384
10385
10386
10387
10388
10389
10390
10391
10392
10393
10394
10395
10396
10397
10398
10399
10400
10401
10402
10403
10404
10405
10406
10407
10408
10409
10410
10411
10412
10413
10414
10415
10416
10417
10418
10419
10420
10421
10422
10423
10424
10425
10426
10427
10428
10429
10430
10431
10432
10433
10434
10435
10436
10437
10438
10439
10440
10441
10442
10443
10444
10445
10446
10447
10448
10449
10450
10451
10452
10453
10454
10455
10456
10457
10458
10459
10460
10461
10462
10463
10464
10465
10466
10467
10468
10469
10470
10471
10472
10473
10474
10475
10476
10477
10478
10479
10480
10481
10482
10483
10484
10485
10486
10487
10488
10489
10490
10491
10492
10493
10494
10495
10496
10497
10498
10499
10500
10501
10502
10503
10504
10505
10506
10507
10508
10509
10510
10511
10512
10513
10514
10515
10516
10517
10518
10519
10520
10521
10522
10523
10524
10525
10526
10527
10528
10529
10530
10531
10532
10533
10534
10535
10536
10537
10538
10539
10540
10541
10542
10543
10544
10545
10546
10547
10548
10549
10550
10551
10552
10553
10554
10555
10556
10557
10558
10559
10560
10561
10562
10563
10564
10565
10566
10567
10568
10569
10570
10571
10572
10573
10574
10575
10576
10577
10578
10579
10580
10581
10582
10583
10584
10585
10586
10587
10588
10589
10590
10591
10592
10593
10594
10595
10596
10597
10598
10599
10600
10601
10602
10603
10604
10605
10606
10607
10608
10609
10610
10611
10612
10613
10614
10615
10616
10617
10618
10619
10620
10621
10622
10623
10624
10625
10626
10627
10628
10629
10630
10631
10632
10633
10634
10635
10636
10637
10638
10639
10640
10641
10642
10643
10644
10645
10646
10647
10648
10649
10650
10651
10652
10653
10654
10655
10656
10657
10658
10659
10660
10661
10662
10663
10664
10665
10666
10667
10668
10669
10670
10671
10672
10673
10674
10675
10676
10677
10678
10679
10680
10681
10682
10683
10684
10685
10686
10687
10688
10689
10690
10691
10692
10693
10694
10695
10696
10697
10698
10699
10700
10701
10702
10703
10704
10705
10706
10707
10708
10709
10710
10711
10712
10713
10714
10715
10716
10717
10718
10719
10720
10721
10722
10723
10724
10725
10726
10727
10728
10729
10730
10731
10732
10733
10734
10735
10736
10737
10738
10739
10740
10741
10742
10743
10744
10745
10746
10747
10748
10749
10750
10751
10752
10753
10754
10755
10756
10757
10758
10759
10760
10761
10762
10763
10764
10765
10766
10767
10768
10769
10770
10771
10772
10773
10774
10775
10776
10777
10778
10779
10780
10781
10782
10783
10784
10785
10786
10787
10788
10789
10790
10791
10792
10793
10794
10795
10796
10797
10798
10799
10800
10801
10802
10803
10804
10805
10806
10807
10808
10809
10810
10811
10812
10813
10814
10815
10816
10817
10818
10819
10820
10821
10822
10823
10824
10825
10826
10827
10828
10829
10830
10831
10832
10833
10834
10835
10836
10837
10838
10839
10840
10841
10842
10843
10844
10845
10846
10847
10848
10849
10850
10851
10852
10853
10854
10855
10856
10857
10858
10859
10860
10861
10862
10863
10864
10865
10866
10867
10868
10869
10870
10871
10872
10873
10874
10875
10876
10877
10878
10879
10880
10881
10882
10883
10884
10885
10886
10887
10888
10889
10890
10891
10892
10893
10894
10895
10896
10897
10898
10899
10900
10901
10902
10903
10904
10905
10906
10907
10908
10909
10910
10911
10912
10913
10914
10915
10916
10917
10918
10919
10920
10921
10922
10923
10924
10925
10926
10927
10928
10929
10930
10931
10932
10933
10934
10935
10936
10937
10938
10939
10940
10941
10942
10943
10944
10945
10946
10947
10948
10949
10950
10951
10952
10953
10954
10955
10956
10957
10958
10959
10960
10961
10962
10963
10964
10965
10966
10967
10968
10969
10970
10971
10972
10973
10974
10975
10976
10977
10978
10979
10980
10981
10982
10983
10984
10985
10986
10987
10988
10989
10990
10991
10992
10993
10994
10995
10996
10997
10998
10999
11000
11001
11002
11003
11004
11005
11006
11007
11008
11009
11010
11011
11012
11013
11014
11015
11016
11017
11018
11019
11020
11021
11022
11023
11024
11025
11026
11027
11028
11029
11030
11031
11032
11033
11034
11035
11036
11037
11038
11039
11040
11041
11042
11043
11044
11045
11046
11047
11048
11049
11050
11051
11052
11053
11054
11055
11056
11057
11058
11059
11060
11061
11062
11063
11064
11065
11066
11067
11068
11069
11070
11071
11072
11073
11074
11075
11076
11077
11078
11079
11080
11081
11082
11083
11084
11085
11086
11087
11088
11089
11090
11091
11092
11093
11094
11095
11096
11097
11098
11099
11100
11101
11102
11103
11104
11105
11106
11107
11108
11109
11110
11111
11112
11113
11114
11115
11116
11117
11118
11119
11120
11121
11122
11123
11124
11125
11126
11127
11128
11129
11130
11131
11132
11133
11134
11135
11136
11137
11138
11139
11140
11141
11142
11143
11144
11145
11146
11147
11148
11149
11150
11151
11152
11153
11154
11155
11156
11157
11158
11159
11160
11161
11162
11163
11164
11165
11166
11167
11168
11169
11170
11171
11172
11173
11174
11175
11176
11177
11178
11179
11180
11181
11182
11183
11184
11185
11186
11187
11188
11189
11190
11191
11192
11193
11194
11195
11196
11197
11198
11199
11200
11201
11202
11203
11204
11205
11206
11207
11208
11209
11210
11211
11212
11213
11214
11215
11216
11217
11218
11219
11220
11221
11222
11223
11224
11225
11226
11227
11228
11229
11230
11231
11232
11233
11234
11235
11236
11237
11238
11239
11240
11241
11242
11243
11244
11245
11246
11247
11248
11249
11250
11251
11252
11253
11254
11255
11256
11257
11258
11259
11260
11261
11262
11263
11264
11265
11266
11267
11268
11269
11270
11271
11272
11273
11274
11275
11276
11277
11278
11279
11280
11281
11282
11283
11284
11285
11286
11287
11288
11289
11290
11291
11292
11293
11294
11295
11296
11297
11298
11299
11300
11301
11302
11303
11304
11305
11306
11307
11308
11309
11310
11311
11312
11313
11314
11315
11316
11317
11318
11319
11320
11321
11322
11323
11324
11325
11326
11327
11328
11329
11330
11331
11332
11333
11334
11335
11336
11337
11338
11339
11340
11341
11342
11343
11344
11345
11346
11347
11348
11349
11350
11351
11352
11353
11354
11355
11356
11357
11358
11359
11360
11361
11362
11363
11364
11365
11366
11367
11368
11369
11370
11371
11372
11373
11374
11375
11376
11377
11378
11379
11380
11381
11382
11383
11384
11385
11386
11387
11388
11389
11390
11391
11392
11393
11394
11395
11396
11397
11398
11399
11400
11401
11402
11403
11404
11405
11406
11407
11408
11409
11410
11411
11412
11413
11414
11415
11416
11417
11418
11419
11420
11421
11422
11423
11424
11425
11426
11427
11428
11429
11430
11431
11432
11433
11434
11435
11436
11437
11438
11439
11440
11441
11442
11443
11444
11445
11446
11447
11448
11449
11450
11451
11452
11453
11454
11455
11456
11457
11458
11459
11460
11461
11462
11463
11464
11465
11466
11467
11468
11469
11470
11471
11472
11473
11474
11475
11476
11477
11478
11479
11480
11481
11482
11483
11484
11485
11486
11487
11488
11489
11490
11491
11492
11493
11494
11495
11496
11497
11498
11499
11500
11501
11502
11503
11504
11505
11506
11507
11508
11509
11510
11511
11512
11513
11514
11515
11516
11517
11518
11519
11520
11521
11522
11523
11524
11525
11526
11527
11528
11529
11530
11531
11532
11533
11534
11535
11536
11537
11538
11539
11540
11541
11542
11543
11544
11545
11546
11547
11548
11549
11550
11551
11552
11553
11554
11555
11556
11557
11558
11559
11560
11561
11562
11563
11564
11565
11566
11567
11568
11569
11570
11571
11572
11573
11574
11575
11576
11577
11578
11579
11580
11581
11582
11583
11584
11585
11586
11587
11588
11589
11590
11591
11592
11593
11594
11595
11596
11597
11598
11599
11600
11601
11602
11603
11604
11605
11606
11607
11608
11609
11610
11611
11612
11613
11614
11615
11616
11617
11618
11619
11620
11621
11622
11623
11624
11625
11626
11627
11628
11629
11630
11631
11632
11633
11634
11635
11636
11637
11638
11639
11640
11641
11642
11643
11644
11645
11646
11647
11648
11649
11650
11651
11652
11653
11654
11655
11656
11657
11658
11659
11660
11661
11662
11663
11664
11665
11666
11667
11668
11669
11670
11671
11672
11673
11674
11675
11676
11677
11678
11679
11680
11681
11682
11683
11684
11685
11686
11687
11688
11689
11690
11691
11692
11693
11694
11695
11696
11697
11698
11699
11700
11701
11702
11703
11704
11705
11706
11707
11708
11709
11710
11711
11712
11713
11714
11715
11716
11717
11718
11719
11720
11721
11722
11723
11724
11725
11726
11727
11728
11729
11730
11731
11732
11733
11734
11735
11736
11737
11738
11739
11740
11741
11742
11743
11744
11745
11746
11747
11748
11749
11750
11751
11752
11753
11754
11755
11756
11757
11758
11759
11760
11761
11762
11763
11764
11765
11766
11767
11768
11769
11770
11771
11772
11773
11774
11775
11776
11777
11778
11779
11780
11781
11782
11783
11784
11785
11786
11787
11788
11789
11790
11791
11792
11793
11794
11795
11796
11797
11798
11799
11800
11801
11802
11803
11804
11805
11806
11807
11808
11809
11810
11811
11812
11813
11814
11815
11816
11817
11818
11819
11820
11821
11822
11823
11824
11825
11826
11827
11828
11829
11830
11831
11832
11833
11834
11835
11836
11837
11838
11839
11840
11841
11842
11843
11844
11845
11846
11847
11848
11849
11850
11851
11852
11853
11854
11855
11856
11857
11858
11859
11860
11861
11862
11863
11864
11865
11866
11867
11868
11869
11870
11871
11872
11873
11874
11875
11876
11877
11878
11879
11880
11881
11882
11883
11884
11885
11886
11887
11888
11889
11890
11891
11892
11893
11894
11895
11896
11897
11898
11899
11900
11901
11902
11903
11904
11905
11906
11907
11908
11909
11910
11911
11912
11913
11914
11915
11916
11917
11918
11919
11920
11921
11922
11923
11924
11925
11926
11927
11928
11929
11930
11931
11932
11933
11934
11935
11936
11937
11938
11939
11940
11941
11942
11943
11944
11945
11946
11947
11948
11949
11950
11951
11952
11953
11954
11955
11956
11957
11958
11959
11960
11961
11962
11963
11964
11965
11966
11967
11968
11969
11970
11971
11972
11973
11974
11975
11976
11977
11978
11979
11980
11981
11982
11983
11984
11985
11986
11987
11988
11989
11990
11991
11992
11993
11994
11995
11996
11997
11998
11999
12000
12001
12002
12003
12004
12005
12006
12007
12008
12009
12010
12011
12012
12013
12014
12015
12016
12017
12018
12019
12020
12021
12022
12023
12024
12025
12026
12027
12028
12029
12030
12031
12032
12033
12034
12035
12036
12037
12038
12039
12040
12041
12042
12043
12044
12045
12046
12047
12048
12049
12050
12051
12052
12053
12054
12055
12056
12057
12058
12059
12060
12061
12062
12063
12064
12065
12066
12067
12068
12069
12070
12071
12072
12073
12074
12075
12076
12077
12078
12079
12080
12081
12082
12083
12084
12085
12086
12087
12088
12089
12090
12091
12092
12093
12094
12095
12096
12097
12098
12099
12100
12101
12102
12103
12104
12105
12106
12107
12108
12109
12110
12111
12112
12113
12114
12115
12116
12117
12118
12119
12120
12121
12122
12123
12124
12125
12126
12127
12128
12129
12130
12131
12132
12133
12134
12135
12136
12137
12138
12139
12140
12141
12142
12143
12144
12145
12146
12147
12148
12149
12150
12151
12152
12153
12154
12155
12156
12157
12158
12159
12160
12161
12162
12163
12164
12165
12166
12167
12168
12169
12170
12171
12172
12173
12174
12175
12176
12177
12178
12179
12180
12181
12182
12183
12184
12185
12186
12187
12188
12189
12190
12191
12192
12193
12194
12195
12196
12197
12198
12199
12200
12201
12202
12203
12204
12205
12206
12207
12208
12209
12210
12211
12212
12213
12214
12215
12216
12217
12218
12219
12220
12221
12222
12223
12224
12225
12226
12227
12228
12229
12230
12231
12232
12233
12234
12235
12236
12237
12238
12239
12240
12241
12242
12243
12244
12245
12246
12247
12248
12249
12250
12251
12252
12253
12254
12255
12256
12257
12258
12259
12260
12261
12262
12263
12264
12265
12266
12267
12268
12269
12270
12271
12272
12273
12274
12275
12276
12277
12278
12279
12280
12281
12282
12283
12284
12285
12286
12287
12288
12289
12290
12291
12292
12293
12294
12295
12296
12297
12298
12299
12300
12301
12302
12303
12304
12305
12306
12307
12308
12309
12310
12311
12312
12313
12314
12315
12316
12317
12318
12319
12320
12321
12322
12323
12324
12325
12326
12327
12328
12329
12330
12331
12332
12333
12334
12335
12336
12337
12338
12339
12340
12341
12342
12343
12344
12345
12346
12347
12348
12349
12350
12351
12352
12353
12354
12355
12356
12357
12358
12359
12360
12361
12362
12363
12364
12365
12366
12367
12368
12369
12370
12371
12372
12373
12374
12375
12376
12377
12378
12379
12380
12381
12382
12383
12384
12385
12386
12387
12388
12389
12390
12391
12392
12393
12394
12395
12396
12397
12398
12399
12400
12401
12402
12403
12404
12405
12406
12407
12408
12409
12410
12411
12412
12413
12414
12415
12416
12417
12418
12419
12420
12421
12422
12423
12424
12425
12426
12427
12428
12429
12430
12431
12432
12433
12434
12435
12436
12437
12438
12439
12440
12441
12442
12443
12444
12445
12446
12447
12448
12449
12450
12451
12452
12453
12454
12455
12456
12457
12458
12459
12460
12461
12462
12463
12464
12465
12466
12467
12468
12469
12470
12471
12472
12473
12474
12475
12476
12477
12478
12479
12480
12481
12482
12483
12484
12485
12486
12487
12488
12489
12490
12491
12492
12493
12494
12495
12496
12497
12498
12499
12500
12501
12502
12503
12504
12505
12506
12507
12508
12509
12510
12511
12512
12513
12514
12515
12516
12517
12518
12519
12520
12521
12522
12523
12524
12525
12526
12527
12528
12529
12530
12531
12532
12533
12534
12535
12536
12537
12538
12539
12540
12541
12542
12543
12544
12545
12546
12547
12548
12549
12550
12551
12552
12553
12554
12555
12556
12557
12558
12559
12560
12561
12562
12563
12564
12565
12566
12567
12568
12569
12570
12571
12572
12573
12574
12575
12576
12577
12578
12579
12580
12581
12582
12583
12584
12585
12586
12587
12588
12589
12590
12591
12592
12593
12594
12595
12596
12597
12598
12599
12600
12601
12602
12603
12604
12605
12606
12607
12608
12609
12610
12611
12612
12613
12614
12615
12616
12617
12618
12619
12620
12621
12622
12623
12624
12625
12626
12627
12628
12629
12630
12631
12632
12633
12634
12635
12636
12637
12638
12639
12640
12641
12642
12643
12644
12645
12646
12647
12648
12649
12650
12651
12652
12653
12654
12655
12656
12657
12658
12659
12660
12661
12662
12663
12664
12665
12666
12667
12668
12669
12670
12671
12672
12673
12674
12675
12676
12677
12678
12679
12680
12681
12682
12683
12684
12685
12686
12687
12688
12689
12690
12691
12692
12693
12694
12695
12696
12697
12698
12699
12700
12701
12702
12703
12704
12705
12706
12707
12708
12709
12710
12711
12712
12713
12714
12715
12716
12717
12718
12719
12720
12721
12722
12723
12724
12725
12726
12727
12728
12729
12730
12731
12732
12733
12734
12735
12736
12737
12738
12739
12740
12741
12742
12743
12744
12745
12746
12747
12748
12749
12750
12751
12752
12753
12754
12755
12756
12757
12758
12759
12760
12761
12762
12763
12764
12765
12766
12767
12768
12769
12770
12771
12772
12773
12774
12775
12776
12777
12778
12779
12780
12781
12782
12783
12784
12785
12786
12787
12788
12789
12790
12791
12792
12793
12794
12795
12796
12797
12798
12799
12800
12801
12802
12803
12804
12805
12806
12807
12808
12809
12810
12811
12812
12813
12814
12815
12816
12817
12818
12819
12820
12821
12822
12823
12824
12825
12826
12827
12828
12829
12830
12831
12832
12833
12834
12835
12836
12837
12838
12839
12840
12841
12842
12843
12844
12845
12846
12847
12848
12849
12850
12851
12852
12853
12854
12855
12856
12857
12858
12859
12860
12861
12862
12863
12864
12865
12866
12867
12868
12869
12870
12871
12872
12873
12874
12875
12876
12877
12878
12879
12880
12881
12882
12883
12884
12885
12886
12887
12888
12889
12890
12891
12892
12893
12894
12895
12896
12897
12898
12899
12900
12901
12902
12903
12904
12905
12906
12907
12908
12909
12910
12911
12912
12913
12914
12915
12916
12917
12918
12919
12920
12921
12922
12923
12924
12925
12926
12927
12928
12929
12930
12931
12932
12933
12934
12935
12936
12937
12938
12939
12940
12941
12942
12943
12944
12945
12946
12947
12948
12949
12950
12951
12952
12953
12954
12955
12956
12957
12958
12959
12960
12961
12962
12963
12964
12965
12966
12967
12968
12969
12970
12971
12972
12973
12974
12975
12976
12977
12978
12979
12980
12981
12982
12983
12984
12985
12986
12987
12988
12989
12990
12991
12992
12993
12994
12995
12996
12997
12998
12999
13000
13001
13002
13003
13004
13005
13006
13007
13008
13009
13010
13011
13012
13013
13014
13015
13016
13017
13018
13019
13020
13021
13022
13023
13024
13025
13026
13027
13028
13029
13030
13031
13032
13033
13034
13035
13036
13037
13038
13039
13040
13041
13042
13043
13044
13045
13046
13047
13048
13049
13050
13051
13052
13053
13054
13055
13056
13057
13058
13059
13060
13061
13062
13063
13064
13065
13066
13067
13068
13069
13070
13071
13072
13073
13074
13075
13076
13077
13078
13079
13080
13081
13082
13083
13084
13085
13086
13087
13088
13089
13090
13091
13092
13093
13094
13095
13096
13097
13098
13099
13100
13101
13102
13103
13104
13105
13106
13107
13108
13109
13110
13111
13112
13113
13114
13115
13116
13117
13118
13119
13120
13121
13122
13123
13124
13125
13126
13127
13128
13129
13130
13131
13132
13133
13134
13135
13136
13137
13138
13139
13140
13141
13142
13143
13144
13145
13146
13147
13148
13149
13150
13151
13152
13153
13154
13155
13156
13157
13158
13159
13160
13161
13162
13163
13164
13165
13166
13167
13168
13169
13170
13171
13172
13173
13174
13175
13176
13177
13178
13179
13180
13181
13182
13183
13184
13185
13186
13187
13188
13189
13190
13191
13192
13193
13194
13195
13196
13197
13198
13199
13200
13201
13202
13203
13204
13205
13206
13207
13208
13209
13210
13211
13212
13213
13214
13215
13216
13217
13218
13219
13220
13221
13222
13223
13224
13225
13226
13227
13228
13229
13230
13231
13232
13233
13234
13235
13236
13237
13238
13239
13240
13241
13242
13243
13244
13245
13246
13247
13248
13249
13250
13251
13252
13253
13254
13255
13256
13257
13258
13259
13260
13261
13262
13263
13264
13265
13266
13267
13268
13269
13270
13271
13272
13273
13274
13275
13276
13277
13278
13279
13280
13281
13282
13283
13284
13285
13286
13287
13288
13289
13290
13291
13292
13293
13294
13295
13296
13297
13298
13299
13300
13301
13302
13303
13304
13305
13306
13307
13308
13309
13310
13311
13312
13313
13314
13315
13316
13317
13318
13319
13320
13321
13322
13323
13324
13325
13326
13327
13328
13329
13330
13331
13332
13333
13334
13335
13336
13337
13338
13339
13340
13341
13342
13343
13344
13345
13346
13347
13348
13349
13350
13351
13352
13353
13354
13355
13356
13357
13358
13359
13360
13361
13362
13363
13364
13365
13366
13367
13368
13369
13370
13371
13372
13373
13374
13375
13376
13377
13378
13379
13380
13381
13382
13383
13384
13385
13386
13387
13388
13389
13390
13391
13392
13393
13394
13395
13396
13397
13398
13399
13400
13401
13402
13403
13404
13405
13406
13407
13408
13409
13410
13411
13412
13413
13414
13415
13416
13417
13418
13419
13420
13421
13422
13423
13424
13425
13426
13427
13428
13429
13430
13431
13432
13433
13434
13435
13436
13437
13438
13439
13440
13441
13442
13443
13444
13445
13446
13447
13448
13449
13450
13451
13452
13453
13454
13455
13456
13457
13458
13459
13460
13461
13462
13463
13464
13465
13466
13467
13468
13469
13470
13471
13472
13473
13474
13475
13476
13477
13478
13479
13480
13481
13482
13483
13484
13485
13486
13487
13488
13489
13490
13491
13492
13493
13494
13495
13496
13497
13498
13499
13500
13501
13502
13503
13504
13505
13506
13507
13508
13509
13510
13511
13512
13513
13514
13515
13516
13517
13518
13519
13520
13521
13522
13523
13524
13525
13526
13527
13528
13529
13530
13531
13532
13533
13534
13535
13536
13537
13538
13539
13540
13541
13542
13543
13544
13545
13546
13547
13548
13549
13550
13551
13552
13553
13554
13555
13556
13557
13558
13559
13560
13561
13562
13563
13564
13565
13566
13567
13568
13569
13570
13571
13572
13573
13574
13575
13576
13577
13578
13579
13580
13581
13582
13583
13584
13585
13586
13587
13588
13589
13590
13591
13592
13593
13594
13595
13596
13597
13598
13599
13600
13601
13602
13603
13604
13605
13606
13607
13608
13609
13610
13611
13612
13613
13614
13615
13616
13617
13618
13619
13620
13621
13622
13623
13624
13625
13626
13627
13628
13629
13630
13631
13632
13633
13634
13635
13636
13637
13638
13639
13640
13641
13642
13643
13644
13645
13646
13647
13648
13649
13650
13651
13652
13653
13654
13655
13656
13657
13658
13659
13660
13661
13662
13663
13664
13665
13666
13667
13668
13669
13670
13671
13672
13673
13674
13675
13676
13677
13678
13679
13680
13681
13682
13683
13684
13685
13686
13687
13688
13689
13690
13691
13692
13693
13694
13695
13696
13697
13698
13699
13700
13701
13702
13703
13704
13705
13706
13707
13708
13709
13710
13711
13712
13713
13714
13715
13716
13717
13718
13719
13720
13721
13722
13723
13724
13725
13726
13727
13728
13729
13730
13731
13732
13733
13734
13735
13736
13737
13738
13739
13740
13741
13742
13743
13744
13745
13746
13747
13748
13749
13750
13751
13752
13753
13754
13755
13756
13757
13758
13759
13760
13761
13762
13763
13764
13765
13766
13767
13768
13769
13770
13771
13772
13773
13774
13775
13776
13777
13778
13779
13780
13781
13782
13783
13784
13785
13786
13787
13788
13789
13790
13791
13792
13793
13794
13795
13796
13797
13798
13799
13800
13801
13802
13803
13804
13805
13806
13807
13808
13809
13810
13811
13812
13813
13814
13815
13816
13817
13818
13819
13820
13821
13822
13823
13824
13825
13826
13827
13828
13829
13830
13831
13832
13833
13834
13835
13836
13837
13838
13839
13840
13841
13842
13843
13844
13845
13846
13847
13848
13849
13850
13851
13852
13853
13854
13855
13856
13857
13858
13859
13860
13861
13862
13863
13864
13865
13866
13867
13868
13869
13870
13871
13872
13873
13874
13875
13876
13877
13878
13879
13880
13881
13882
13883
13884
13885
13886
13887
13888
13889
13890
13891
13892
13893
13894
13895
13896
13897
13898
13899
13900
13901
13902
13903
13904
13905
13906
13907
13908
13909
13910
13911
13912
13913
13914
13915
13916
13917
13918
13919
13920
13921
13922
13923
13924
13925
13926
13927
13928
13929
13930
13931
13932
13933
13934
13935
13936
13937
13938
13939
13940
13941
13942
13943
13944
13945
13946
13947
13948
13949
13950
13951
13952
13953
13954
13955
13956
13957
13958
13959
13960
13961
13962
13963
13964
13965
13966
13967
13968
13969
13970
13971
13972
13973
13974
13975
13976
13977
13978
13979
13980
13981
13982
13983
13984
13985
13986
13987
13988
13989
13990
13991
13992
13993
13994
13995
13996
13997
13998
13999
14000
14001
14002
14003
14004
14005
14006
14007
14008
14009
14010
14011
14012
14013
14014
14015
14016
14017
14018
14019
14020
14021
14022
14023
14024
14025
14026
14027
14028
14029
14030
14031
14032
14033
14034
14035
14036
14037
14038
14039
14040
14041
14042
14043
14044
14045
14046
14047
14048
14049
14050
14051
14052
14053
14054
14055
14056
14057
14058
14059
14060
14061
14062
14063
14064
14065
14066
14067
14068
14069
14070
14071
14072
14073
14074
14075
14076
14077
14078
14079
14080
14081
14082
14083
14084
14085
14086
14087
14088
14089
14090
14091
14092
14093
14094
14095
14096
14097
14098
14099
14100
14101
14102
14103
14104
14105
14106
14107
14108
14109
14110
14111
14112
14113
14114
14115
14116
14117
14118
14119
14120
14121
14122
14123
14124
14125
14126
14127
14128
14129
14130
14131
14132
14133
14134
14135
14136
14137
14138
14139
14140
14141
14142
14143
14144
14145
14146
14147
14148
14149
14150
14151
14152
14153
14154
14155
14156
14157
14158
14159
14160
14161
14162
14163
14164
14165
14166
14167
14168
14169
14170
14171
14172
14173
14174
14175
14176
14177
14178
14179
14180
14181
14182
14183
14184
14185
14186
14187
14188
14189
14190
14191
14192
14193
14194
14195
14196
14197
14198
14199
14200
14201
14202
14203
14204
14205
14206
14207
14208
14209
14210
14211
14212
14213
14214
14215
14216
14217
14218
14219
14220
14221
14222
14223
14224
14225
14226
14227
14228
14229
14230
14231
14232
14233
14234
14235
14236
14237
14238
14239
14240
14241
14242
14243
14244
14245
14246
14247
14248
14249
14250
14251
14252
14253
14254
14255
14256
14257
14258
14259
14260
14261
14262
14263
14264
14265
14266
14267
14268
14269
14270
14271
14272
14273
14274
14275
14276
14277
14278
14279
14280
14281
14282
14283
14284
14285
14286
14287
14288
14289
14290
14291
14292
14293
14294
14295
14296
14297
14298
14299
14300
14301
14302
14303
14304
14305
14306
14307
14308
14309
14310
14311
14312
14313
14314
14315
14316
14317
14318
14319
14320
14321
14322
14323
14324
14325
14326
14327
14328
14329
14330
14331
14332
14333
14334
14335
14336
14337
14338
14339
14340
14341
14342
14343
14344
14345
14346
14347
14348
14349
14350
14351
14352
14353
14354
14355
14356
14357
14358
14359
14360
14361
14362
14363
14364
14365
14366
14367
14368
14369
14370
14371
14372
14373
14374
14375
14376
14377
14378
14379
14380
14381
14382
14383
14384
14385
14386
14387
14388
14389
14390
14391
14392
14393
14394
14395
14396
14397
14398
14399
14400
14401
14402
14403
14404
14405
14406
14407
14408
14409
14410
14411
14412
14413
14414
14415
14416
14417
14418
14419
14420
14421
14422
14423
14424
14425
14426
14427
14428
14429
14430
14431
14432
14433
14434
14435
14436
14437
14438
14439
14440
14441
14442
14443
14444
14445
14446
14447
14448
14449
14450
14451
14452
14453
14454
14455
14456
14457
14458
14459
14460
14461
14462
14463
14464
14465
14466
14467
14468
14469
14470
14471
14472
14473
14474
14475
14476
14477
14478
14479
14480
14481
14482
14483
14484
14485
14486
14487
14488
14489
14490
14491
14492
14493
14494
14495
14496
14497
14498
14499
14500
14501
14502
14503
14504
14505
14506
14507
14508
14509
14510
14511
14512
14513
14514
14515
14516
14517
14518
14519
14520
14521
14522
14523
14524
14525
14526
14527
14528
14529
14530
14531
14532
14533
14534
14535
14536
14537
14538
14539
14540
14541
14542
14543
14544
14545
14546
14547
14548
14549
14550
14551
14552
14553
14554
14555
14556
14557
14558
14559
14560
14561
14562
14563
14564
14565
14566
14567
14568
14569
14570
14571
14572
14573
14574
14575
14576
14577
14578
14579
14580
14581
14582
14583
14584
14585
14586
14587
14588
14589
14590
14591
14592
14593
14594
14595
14596
14597
14598
14599
14600
14601
14602
14603
14604
14605
14606
14607
14608
14609
14610
14611
14612
14613
14614
14615
14616
14617
14618
14619
14620
14621
14622
14623
14624
14625
14626
14627
14628
14629
14630
14631
14632
14633
14634
14635
14636
14637
14638
14639
14640
14641
14642
14643
14644
14645
14646
14647
14648
14649
14650
14651
14652
14653
14654
14655
14656
14657
14658
14659
14660
14661
14662
14663
14664
14665
14666
14667
14668
14669
14670
14671
14672
14673
14674
14675
14676
14677
14678
14679
14680
14681
14682
14683
14684
14685
14686
14687
14688
14689
14690
14691
14692
14693
14694
14695
14696
14697
14698
14699
14700
14701
14702
14703
14704
14705
14706
14707
14708
14709
14710
14711
14712
14713
14714
14715
14716
14717
14718
14719
14720
14721
14722
14723
14724
14725
14726
14727
14728
14729
14730
14731
14732
14733
14734
14735
14736
14737
14738
14739
14740
14741
14742
14743
14744
14745
14746
14747
14748
14749
14750
14751
14752
14753
14754
14755
14756
14757
14758
14759
14760
14761
14762
14763
14764
14765
14766
14767
14768
14769
14770
14771
14772
14773
14774
14775
14776
14777
14778
14779
14780
14781
14782
14783
14784
14785
14786
14787
14788
14789
14790
14791
14792
14793
14794
14795
14796
14797
14798
14799
14800
14801
14802
14803
14804
14805
14806
14807
14808
14809
14810
14811
14812
14813
14814
14815
14816
14817
14818
14819
14820
14821
14822
14823
14824
14825
14826
14827
14828
14829
14830
14831
14832
14833
14834
14835
14836
14837
14838
14839
14840
14841
14842
14843
14844
14845
14846
14847
14848
14849
14850
14851
14852
14853
14854
14855
14856
14857
14858
14859
14860
14861
14862
14863
14864
14865
14866
14867
14868
14869
14870
14871
14872
14873
14874
14875
14876
14877
14878
14879
14880
14881
14882
14883
14884
14885
14886
14887
14888
14889
14890
14891
14892
14893
14894
14895
14896
14897
14898
14899
14900
14901
14902
14903
14904
14905
14906
14907
14908
14909
14910
14911
14912
14913
14914
14915
14916
14917
14918
14919
14920
14921
14922
14923
14924
14925
14926
14927
14928
14929
14930
14931
14932
14933
14934
14935
14936
14937
14938
14939
14940
14941
14942
14943
14944
14945
14946
14947
14948
14949
14950
14951
14952
14953
14954
14955
14956
14957
14958
14959
14960
14961
14962
14963
14964
14965
14966
14967
14968
14969
14970
14971
14972
14973
14974
14975
14976
14977
14978
14979
14980
14981
14982
14983
14984
14985
14986
14987
14988
14989
14990
14991
14992
14993
14994
14995
14996
14997
14998
14999
15000
15001
15002
15003
15004
15005
15006
15007
15008
15009
15010
15011
15012
15013
15014
15015
15016
15017
15018
15019
15020
15021
15022
15023
15024
15025
15026
15027
15028
15029
15030
15031
15032
15033
15034
15035
15036
15037
15038
15039
15040
15041
15042
15043
15044
15045
15046
15047
15048
15049
15050
15051
15052
15053
15054
15055
15056
15057
15058
15059
15060
15061
15062
15063
15064
15065
15066
15067
15068
15069
15070
15071
15072
15073
15074
15075
15076
15077
15078
15079
15080
15081
15082
15083
15084
15085
15086
15087
15088
15089
15090
15091
15092
15093
15094
15095
15096
15097
15098
15099
15100
15101
15102
15103
15104
15105
15106
15107
15108
15109
15110
15111
15112
15113
15114
15115
15116
15117
15118
15119
15120
15121
15122
15123
15124
15125
15126
15127
15128
15129
15130
15131
15132
15133
15134
15135
15136
15137
15138
15139
15140
15141
15142
15143
15144
15145
15146
15147
15148
15149
15150
15151
15152
15153
15154
15155
15156
15157
15158
15159
15160
15161
15162
15163
15164
15165
15166
15167
15168
15169
15170
15171
15172
15173
15174
15175
15176
15177
15178
15179
15180
15181
15182
15183
15184
15185
15186
15187
15188
15189
15190
15191
15192
15193
15194
15195
15196
15197
15198
15199
15200
15201
15202
15203
15204
15205
15206
15207
15208
15209
15210
15211
15212
15213
15214
15215
15216
15217
15218
15219
15220
15221
15222
15223
15224
15225
15226
15227
15228
15229
15230
15231
15232
15233
15234
15235
15236
15237
15238
15239
15240
15241
15242
15243
15244
15245
15246
15247
15248
15249
15250
15251
15252
15253
15254
15255
15256
15257
15258
15259
15260
15261
15262
15263
15264
15265
15266
15267
15268
15269
15270
15271
15272
15273
15274
15275
15276
15277
15278
15279
15280
15281
15282
15283
15284
15285
15286
15287
15288
15289
15290
15291
15292
15293
15294
15295
15296
15297
15298
15299
15300
15301
15302
15303
15304
15305
15306
15307
15308
15309
15310
15311
15312
15313
15314
15315
15316
15317
15318
15319
15320
15321
15322
15323
15324
15325
15326
15327
15328
15329
15330
15331
15332
15333
15334
15335
15336
15337
15338
15339
15340
15341
15342
15343
15344
15345
15346
15347
15348
15349
15350
15351
15352
15353
15354
15355
15356
15357
15358
15359
15360
15361
15362
15363
15364
15365
15366
15367
15368
15369
15370
15371
15372
15373
15374
15375
15376
15377
15378
15379
15380
15381
15382
15383
15384
15385
15386
15387
15388
15389
15390
15391
15392
15393
15394
15395
15396
15397
15398
15399
15400
15401
15402
15403
15404
15405
15406
15407
15408
15409
15410
15411
15412
15413
15414
15415
15416
15417
15418
15419
15420
15421
15422
15423
15424
15425
15426
15427
15428
15429
15430
15431
15432
15433
15434
15435
15436
15437
15438
15439
15440
15441
15442
15443
15444
15445
15446
15447
15448
15449
15450
15451
15452
15453
15454
15455
15456
15457
15458
15459
15460
15461
15462
15463
15464
15465
15466
15467
15468
15469
15470
15471
15472
15473
15474
15475
15476
15477
15478
15479
15480
15481
15482
15483
15484
15485
15486
15487
15488
15489
15490
15491
15492
15493
15494
15495
15496
15497
15498
15499
15500
15501
15502
15503
15504
15505
15506
15507
15508
15509
15510
15511
15512
15513
15514
15515
15516
15517
15518
15519
15520
15521
15522
15523
15524
15525
15526
15527
15528
15529
15530
15531
15532
15533
15534
15535
15536
15537
15538
15539
15540
15541
15542
15543
15544
15545
15546
15547
15548
15549
15550
15551
15552
15553
15554
15555
15556
15557
15558
15559
15560
15561
15562
15563
15564
15565
15566
15567
15568
15569
15570
15571
15572
15573
15574
15575
15576
15577
15578
15579
15580
15581
15582
15583
15584
15585
15586
15587
15588
15589
15590
15591
15592
15593
15594
15595
15596
15597
15598
15599
15600
15601
15602
15603
15604
15605
15606
15607
15608
15609
15610
15611
15612
15613
15614
15615
15616
15617
15618
15619
15620
15621
15622
15623
15624
15625
15626
15627
15628
15629
15630
15631
15632
15633
15634
15635
15636
15637
15638
15639
15640
15641
15642
15643
15644
15645
15646
15647
15648
15649
15650
15651
15652
15653
15654
15655
15656
15657
15658
15659
15660
15661
15662
15663
15664
15665
15666
15667
15668
15669
15670
15671
15672
15673
15674
15675
15676
15677
15678
15679
15680
15681
15682
15683
15684
15685
15686
15687
15688
15689
15690
15691
15692
15693
15694
15695
15696
15697
15698
15699
15700
15701
15702
15703
15704
15705
15706
15707
15708
15709
15710
15711
15712
15713
15714
15715
15716
15717
15718
15719
15720
15721
15722
15723
15724
15725
15726
15727
15728
15729
15730
15731
15732
15733
15734
15735
15736
15737
15738
15739
15740
15741
15742
15743
15744
15745
15746
15747
15748
15749
15750
15751
15752
15753
15754
15755
15756
15757
15758
15759
15760
15761
15762
15763
15764
15765
15766
15767
15768
15769
15770
15771
15772
15773
15774
15775
15776
15777
15778
15779
15780
15781
15782
15783
15784
15785
15786
15787
15788
15789
15790
15791
15792
15793
15794
15795
15796
15797
15798
15799
15800
15801
15802
15803
15804
15805
15806
15807
15808
15809
15810
15811
15812
15813
15814
15815
15816
15817
15818
15819
15820
15821
15822
15823
15824
15825
15826
15827
15828
15829
15830
15831
15832
15833
15834
15835
15836
15837
15838
15839
15840
15841
15842
15843
15844
15845
15846
15847
15848
15849
15850
15851
15852
15853
15854
15855
15856
15857
15858
15859
15860
15861
15862
15863
15864
15865
15866
15867
15868
15869
15870
15871
15872
15873
15874
15875
15876
15877
15878
15879
15880
15881
15882
15883
15884
15885
15886
15887
15888
15889
15890
15891
15892
15893
15894
15895
15896
15897
15898
15899
15900
15901
15902
15903
15904
15905
15906
15907
15908
15909
15910
15911
15912
15913
15914
15915
15916
15917
15918
15919
15920
15921
15922
15923
15924
15925
15926
15927
15928
15929
15930
15931
15932
15933
15934
15935
15936
15937
15938
15939
15940
15941
15942
15943
15944
15945
15946
15947
15948
15949
15950
15951
15952
15953
15954
15955
15956
15957
15958
15959
15960
15961
15962
15963
15964
15965
15966
15967
15968
15969
15970
15971
15972
15973
15974
15975
15976
15977
15978
15979
15980
15981
15982
15983
15984
15985
15986
15987
15988
15989
15990
15991
15992
15993
15994
15995
15996
15997
15998
15999
16000
16001
16002
16003
16004
16005
16006
16007
16008
16009
16010
16011
16012
16013
16014
16015
16016
16017
16018
16019
16020
16021
16022
16023
16024
16025
16026
16027
16028
16029
16030
16031
16032
16033
16034
16035
16036
16037
16038
16039
16040
16041
16042
16043
16044
16045
16046
16047
16048
16049
16050
16051
16052
16053
16054
16055
16056
16057
16058
16059
16060
16061
16062
16063
16064
16065
16066
16067
16068
16069
16070
16071
16072
16073
16074
16075
16076
16077
16078
16079
16080
16081
16082
16083
16084
16085
16086
16087
16088
16089
16090
16091
16092
16093
16094
16095
16096
16097
16098
16099
16100
16101
16102
16103
16104
16105
16106
16107
16108
16109
16110
16111
16112
16113
16114
16115
16116
16117
16118
16119
16120
16121
16122
16123
16124
16125
16126
16127
16128
16129
16130
16131
16132
16133
16134
16135
16136
16137
16138
16139
16140
16141
16142
16143
16144
16145
16146
16147
16148
16149
16150
16151
16152
16153
16154
16155
16156
16157
16158
16159
16160
16161
16162
16163
16164
16165
16166
16167
16168
16169
16170
16171
16172
16173
16174
16175
16176
16177
16178
16179
16180
16181
16182
16183
16184
16185
16186
16187
16188
16189
16190
16191
16192
16193
16194
16195
16196
16197
16198
16199
16200
16201
16202
16203
16204
16205
16206
16207
16208
16209
16210
16211
16212
16213
16214
16215
16216
16217
16218
16219
16220
16221
16222
16223
16224
16225
16226
16227
16228
16229
16230
16231
16232
16233
16234
16235
16236
16237
16238
16239
16240
16241
16242
16243
16244
16245
16246
16247
16248
16249
16250
16251
16252
16253
16254
16255
16256
16257
16258
16259
16260
16261
16262
16263
16264
16265
16266
16267
16268
16269
16270
16271
16272
16273
16274
16275
16276
16277
16278
16279
16280
16281
16282
16283
16284
16285
16286
16287
16288
16289
16290
16291
16292
16293
16294
16295
16296
16297
16298
16299
16300
16301
16302
16303
16304
16305
16306
16307
16308
16309
16310
16311
16312
16313
16314
16315
16316
16317
16318
16319
16320
16321
16322
16323
16324
16325
16326
16327
16328
16329
16330
16331
16332
16333
16334
16335
16336
16337
16338
16339
16340
16341
16342
16343
16344
16345
16346
16347
16348
16349
16350
16351
16352
16353
16354
16355
16356
16357
16358
16359
16360
16361
16362
16363
16364
16365
16366
16367
16368
16369
16370
16371
16372
16373
16374
16375
16376
16377
16378
16379
16380
16381
16382
16383
16384
16385
16386
16387
16388
16389
16390
16391
16392
16393
16394
16395
16396
16397
16398
16399
16400
16401
16402
16403
16404
16405
16406
16407
16408
16409
16410
16411
16412
16413
16414
16415
16416
16417
16418
16419
16420
16421
16422
16423
16424
16425
16426
16427
16428
16429
16430
16431
16432
16433
16434
16435
16436
16437
16438
16439
16440
16441
16442
16443
16444
16445
16446
16447
16448
16449
16450
16451
16452
16453
16454
16455
16456
16457
16458
16459
16460
16461
16462
16463
16464
16465
16466
16467
16468
16469
16470
16471
16472
16473
16474
16475
16476
16477
16478
16479
16480
16481
16482
16483
16484
16485
16486
16487
16488
16489
16490
16491
16492
16493
16494
16495
16496
16497
16498
16499
16500
16501
16502
16503
16504
16505
16506
16507
16508
16509
16510
16511
16512
16513
16514
16515
16516
16517
16518
16519
16520
16521
16522
16523
16524
16525
16526
16527
16528
16529
16530
16531
16532
16533
16534
16535
16536
16537
16538
16539
16540
16541
16542
16543
16544
16545
16546
16547
16548
16549
16550
16551
16552
16553
16554
16555
16556
16557
16558
16559
16560
16561
16562
16563
16564
16565
16566
16567
16568
16569
16570
16571
16572
16573
16574
16575
16576
16577
16578
16579
16580
16581
16582
16583
16584
16585
16586
16587
16588
16589
16590
16591
16592
16593
16594
16595
16596
16597
16598
16599
16600
16601
16602
16603
16604
16605
16606
16607
16608
16609
16610
16611
16612
16613
16614
16615
16616
16617
16618
16619
16620
16621
16622
16623
16624
16625
16626
16627
16628
16629
16630
16631
16632
16633
16634
16635
16636
16637
16638
16639
16640
16641
16642
16643
16644
16645
16646
16647
16648
16649
16650
16651
16652
16653
16654
16655
16656
16657
16658
16659
16660
16661
16662
16663
16664
16665
16666
16667
16668
16669
16670
16671
16672
16673
16674
16675
16676
16677
16678
16679
16680
16681
16682
16683
16684
16685
16686
16687
16688
16689
16690
16691
16692
16693
16694
16695
16696
16697
16698
16699
16700
16701
16702
16703
16704
16705
16706
16707
16708
16709
16710
16711
16712
16713
16714
16715
16716
16717
16718
16719
16720
16721
16722
16723
16724
16725
16726
16727
16728
16729
16730
16731
16732
16733
16734
16735
16736
16737
16738
16739
16740
16741
16742
16743
16744
16745
16746
16747
16748
16749
16750
16751
16752
16753
16754
16755
16756
16757
16758
16759
16760
16761
16762
16763
16764
16765
16766
16767
16768
16769
16770
16771
16772
16773
16774
16775
16776
16777
16778
16779
16780
16781
16782
16783
16784
16785
16786
16787
16788
16789
16790
16791
16792
16793
16794
16795
16796
16797
16798
16799
16800
16801
16802
16803
16804
16805
16806
16807
16808
16809
16810
16811
16812
16813
16814
16815
16816
16817
16818
16819
16820
16821
16822
16823
16824
16825
16826
16827
16828
16829
16830
16831
16832
16833
16834
16835
16836
16837
16838
16839
16840
16841
16842
16843
16844
16845
16846
16847
16848
16849
16850
16851
16852
16853
16854
16855
16856
16857
16858
16859
16860
16861
16862
16863
16864
16865
16866
16867
16868
16869
16870
16871
16872
16873
16874
16875
16876
16877
16878
16879
16880
16881
16882
16883
16884
16885
16886
16887
16888
16889
16890
16891
16892
16893
16894
16895
16896
16897
16898
16899
16900
16901
16902
16903
16904
16905
16906
16907
16908
16909
16910
16911
16912
16913
16914
16915
16916
16917
16918
16919
16920
16921
16922
16923
16924
16925
16926
16927
16928
16929
16930
16931
16932
16933
16934
16935
16936
16937
16938
16939
16940
16941
16942
16943
16944
16945
16946
16947
16948
16949
16950
16951
16952
16953
16954
16955
16956
16957
16958
16959
16960
16961
16962
16963
16964
16965
16966
16967
16968
16969
16970
16971
16972
16973
16974
16975
16976
16977
16978
16979
16980
16981
16982
16983
16984
16985
16986
16987
16988
16989
16990
16991
16992
16993
16994
16995
16996
16997
16998
16999
17000
17001
17002
17003
17004
17005
17006
17007
17008
17009
17010
17011
17012
17013
17014
17015
17016
17017
17018
17019
17020
17021
17022
17023
17024
17025
17026
17027
17028
17029
17030
17031
17032
17033
17034
17035
17036
17037
17038
17039
17040
17041
17042
17043
17044
17045
17046
17047
17048
17049
17050
17051
17052
17053
17054
17055
17056
17057
17058
17059
17060
17061
17062
17063
17064
17065
17066
17067
17068
17069
17070
17071
17072
17073
17074
17075
17076
17077
17078
17079
17080
17081
17082
17083
17084
17085
17086
17087
17088
17089
17090
17091
17092
17093
17094
17095
17096
17097
17098
17099
17100
17101
17102
17103
17104
17105
17106
17107
17108
17109
17110
17111
17112
17113
17114
17115
17116
17117
17118
17119
17120
17121
17122
17123
17124
17125
17126
17127
17128
17129
17130
17131
17132
17133
17134
17135
17136
17137
17138
17139
17140
17141
17142
17143
17144
17145
17146
17147
17148
17149
17150
17151
17152
17153
17154
17155
17156
17157
17158
17159
17160
17161
17162
17163
17164
17165
17166
17167
17168
17169
17170
17171
17172
17173
17174
17175
17176
17177
17178
17179
17180
17181
17182
17183
17184
17185
17186
17187
17188
17189
17190
17191
17192
17193
17194
17195
17196
17197
17198
17199
17200
17201
17202
17203
17204
17205
17206
17207
17208
17209
17210
17211
17212
17213
17214
17215
17216
17217
17218
17219
17220
17221
17222
17223
17224
17225
17226
17227
17228
17229
17230
17231
17232
17233
17234
17235
17236
17237
17238
17239
17240
17241
17242
17243
17244
17245
17246
17247
17248
17249
17250
17251
17252
17253
17254
17255
17256
17257
17258
17259
17260
17261
17262
17263
17264
17265
17266
17267
17268
17269
17270
17271
17272
17273
17274
17275
17276
17277
17278
17279
17280
17281
17282
17283
17284
17285
17286
17287
17288
17289
17290
17291
17292
17293
17294
17295
17296
17297
17298
17299
17300
17301
17302
17303
17304
17305
17306
17307
17308
17309
17310
17311
17312
17313
17314
17315
17316
17317
17318
17319
17320
17321
17322
17323
17324
17325
17326
17327
17328
17329
17330
17331
17332
17333
17334
17335
17336
17337
17338
17339
17340
17341
17342
17343
17344
17345
17346
17347
17348
17349
17350
17351
17352
17353
17354
17355
17356
17357
17358
17359
17360
17361
17362
17363
17364
17365
17366
17367
17368
17369
17370
17371
17372
17373
17374
17375
17376
17377
17378
17379
17380
17381
17382
17383
17384
17385
17386
17387
17388
17389
17390
17391
17392
17393
17394
17395
17396
17397
17398
17399
17400
17401
17402
17403
17404
17405
17406
17407
17408
17409
17410
17411
17412
17413
17414
17415
17416
17417
17418
17419
17420
17421
17422
17423
17424
17425
17426
17427
17428
17429
17430
17431
17432
17433
17434
17435
17436
17437
17438
17439
17440
17441
17442
17443
17444
17445
17446
17447
17448
17449
17450
17451
17452
17453
17454
17455
17456
17457
17458
17459
17460
17461
17462
17463
17464
17465
17466
17467
17468
17469
17470
17471
17472
17473
17474
17475
17476
17477
17478
17479
17480
17481
17482
17483
17484
17485
17486
17487
17488
17489
17490
17491
17492
17493
17494
17495
17496
17497
17498
17499
17500
17501
17502
17503
17504
17505
17506
17507
17508
17509
17510
17511
17512
17513
17514
17515
17516
17517
17518
17519
17520
17521
17522
17523
17524
17525
17526
17527
17528
17529
17530
17531
17532
17533
17534
17535
17536
17537
17538
17539
17540
17541
17542
17543
17544
17545
17546
17547
17548
17549
17550
17551
17552
17553
17554
17555
17556
17557
17558
17559
17560
17561
17562
17563
17564
17565
17566
17567
17568
17569
17570
17571
17572
17573
17574
17575
17576
17577
17578
17579
17580
17581
17582
17583
17584
17585
17586
17587
17588
17589
17590
17591
17592
17593
17594
17595
17596
17597
17598
17599
17600
17601
17602
17603
17604
17605
17606
17607
17608
17609
17610
17611
17612
17613
17614
17615
17616
17617
17618
17619
17620
17621
17622
17623
17624
17625
17626
17627
17628
17629
17630
17631
17632
17633
17634
17635
17636
17637
17638
17639
17640
17641
17642
17643
17644
17645
17646
17647
17648
17649
17650
17651
17652
17653
17654
17655
17656
17657
17658
17659
17660
17661
17662
17663
17664
17665
17666
17667
17668
17669
17670
17671
17672
17673
17674
17675
17676
17677
17678
17679
17680
17681
17682
17683
17684
17685
17686
17687
17688
17689
17690
17691
17692
17693
17694
17695
17696
17697
17698
17699
17700
17701
17702
17703
17704
17705
17706
17707
17708
17709
17710
17711
17712
17713
17714
17715
17716
17717
17718
17719
17720
17721
17722
17723
17724
17725
17726
17727
17728
17729
17730
17731
17732
17733
17734
17735
17736
17737
17738
17739
17740
17741
17742
17743
17744
17745
17746
17747
17748
17749
17750
17751
17752
17753
17754
17755
17756
17757
17758
17759
17760
17761
17762
17763
17764
17765
17766
17767
17768
17769
17770
17771
17772
17773
17774
17775
17776
17777
17778
17779
17780
17781
17782
17783
17784
17785
17786
17787
17788
17789
17790
17791
17792
17793
17794
17795
17796
17797
17798
17799
17800
17801
17802
17803
17804
17805
17806
17807
17808
17809
17810
17811
17812
17813
17814
17815
17816
17817
17818
17819
17820
17821
17822
17823
17824
17825
17826
17827
17828
17829
17830
17831
17832
17833
17834
17835
17836
17837
17838
17839
17840
17841
17842
17843
17844
17845
17846
17847
17848
17849
17850
17851
17852
17853
17854
17855
17856
17857
17858
17859
17860
17861
17862
17863
17864
17865
17866
17867
17868
17869
17870
17871
17872
17873
17874
17875
17876
17877
17878
17879
17880
17881
17882
17883
17884
17885
17886
17887
17888
17889
17890
17891
17892
17893
17894
17895
17896
17897
17898
17899
17900
17901
17902
17903
17904
17905
17906
17907
17908
17909
17910
17911
17912
17913
17914
17915
17916
17917
17918
17919
17920
17921
17922
17923
17924
17925
17926
17927
17928
17929
17930
17931
17932
17933
17934
17935
17936
17937
17938
17939
17940
17941
17942
17943
17944
17945
17946
17947
17948
17949
17950
17951
17952
17953
17954
17955
17956
17957
17958
17959
17960
17961
17962
17963
17964
17965
17966
17967
17968
17969
17970
17971
17972
17973
17974
17975
17976
17977
17978
17979
17980
17981
17982
17983
17984
17985
17986
17987
17988
17989
17990
17991
17992
17993
17994
17995
17996
17997
17998
17999
18000
18001
18002
18003
18004
18005
18006
18007
18008
18009
18010
18011
18012
18013
18014
18015
18016
18017
18018
18019
18020
18021
18022
18023
18024
18025
18026
18027
18028
18029
18030
18031
18032
18033
18034
18035
18036
18037
18038
18039
18040
18041
18042
18043
18044
18045
18046
18047
18048
18049
18050
18051
18052
18053
18054
18055
18056
18057
18058
18059
18060
18061
18062
18063
18064
18065
18066
18067
18068
18069
18070
18071
18072
18073
18074
18075
18076
18077
18078
18079
18080
18081
18082
18083
18084
18085
18086
18087
18088
18089
18090
18091
18092
18093
18094
18095
18096
18097
18098
18099
18100
18101
18102
18103
18104
18105
18106
18107
18108
18109
18110
18111
18112
18113
18114
18115
18116
18117
18118
18119
18120
18121
18122
18123
18124
18125
18126
18127
18128
18129
18130
18131
18132
18133
18134
18135
18136
18137
18138
18139
18140
\input texinfo
@c %**start of header
@setfilename coreutils.info
@settitle GNU Coreutils
@documentencoding UTF-8
@allowcodebreaks false

@c %**end of header

@include version.texi
@include constants.texi

@c Define new indices.
@defcodeindex op
@defcodeindex fl

@c Put everything in one index (arbitrarily chosen to be the concept index).
@syncodeindex fl cp
@syncodeindex fn cp
@syncodeindex ky cp
@syncodeindex op cp
@syncodeindex pg cp
@syncodeindex vr cp

@dircategory Basics
@direntry
* Coreutils: (coreutils).       Core GNU (file, text, shell) utilities.
* Common options: (coreutils)Common options.
* File permissions: (coreutils)File permissions.  Access modes.
* Date input formats: (coreutils)Date input formats.
@end direntry

@c FIXME: the following need documentation
@c * [: (coreutils)[ invocation.                   File/string tests.
@c * pinky: (coreutils)pinky invocation.           FIXME.

@dircategory Individual utilities
@direntry
* arch: (coreutils)arch invocation.             Print machine hardware name.
* base32: (coreutils)base32 invocation.         Base32 encode/decode data.
* base64: (coreutils)base64 invocation.         Base64 encode/decode data.
* basename: (coreutils)basename invocation.     Strip directory and suffix.
* cat: (coreutils)cat invocation.               Concatenate and write files.
* chcon: (coreutils)chcon invocation.           Change SELinux CTX of files.
* chgrp: (coreutils)chgrp invocation.           Change file groups.
* chmod: (coreutils)chmod invocation.           Change access permissions.
* chown: (coreutils)chown invocation.           Change file owners and groups.
* chroot: (coreutils)chroot invocation.         Specify the root directory.
* cksum: (coreutils)cksum invocation.           Print POSIX CRC checksum.
* comm: (coreutils)comm invocation.             Compare sorted files by line.
* cp: (coreutils)cp invocation.                 Copy files.
* csplit: (coreutils)csplit invocation.         Split by context.
* cut: (coreutils)cut invocation.               Print selected parts of lines.
* date: (coreutils)date invocation.             Print/set system date and time.
* dd: (coreutils)dd invocation.                 Copy and convert a file.
* df: (coreutils)df invocation.                 Report file system disk usage.
* dir: (coreutils)dir invocation.               List directories briefly.
* dircolors: (coreutils)dircolors invocation.   Color setup for ls.
* dirname: (coreutils)dirname invocation.       Strip last file name component.
* du: (coreutils)du invocation.                 Report on disk usage.
* echo: (coreutils)echo invocation.             Print a line of text.
* env: (coreutils)env invocation.               Modify the environment.
* expand: (coreutils)expand invocation.         Convert tabs to spaces.
* expr: (coreutils)expr invocation.             Evaluate expressions.
* factor: (coreutils)factor invocation.         Print prime factors
* false: (coreutils)false invocation.           Do nothing, unsuccessfully.
* fmt: (coreutils)fmt invocation.               Reformat paragraph text.
* fold: (coreutils)fold invocation.             Wrap long input lines.
* groups: (coreutils)groups invocation.         Print group names a user is in.
* head: (coreutils)head invocation.             Output the first part of files.
* hostid: (coreutils)hostid invocation.         Print numeric host identifier.
* hostname: (coreutils)hostname invocation.     Print or set system name.
* id: (coreutils)id invocation.                 Print user identity.
* install: (coreutils)install invocation.       Copy files and set attributes.
* join: (coreutils)join invocation.             Join lines on a common field.
* kill: (coreutils)kill invocation.             Send a signal to processes.
* link: (coreutils)link invocation.             Make hard links between files.
* ln: (coreutils)ln invocation.                 Make links between files.
* logname: (coreutils)logname invocation.       Print current login name.
* ls: (coreutils)ls invocation.                 List directory contents.
* md5sum: (coreutils)md5sum invocation.         Print or check MD5 digests.
* mkdir: (coreutils)mkdir invocation.           Create directories.
* mkfifo: (coreutils)mkfifo invocation.         Create FIFOs (named pipes).
* mknod: (coreutils)mknod invocation.           Create special files.
* mktemp: (coreutils)mktemp invocation.         Create temporary files.
* mv: (coreutils)mv invocation.                 Rename files.
* nice: (coreutils)nice invocation.             Modify niceness.
* nl: (coreutils)nl invocation.                 Number lines and write files.
* nohup: (coreutils)nohup invocation.           Immunize to hangups.
* nproc: (coreutils)nproc invocation.           Print the number of processors.
* numfmt: (coreutils)numfmt invocation.         Reformat numbers.
* od: (coreutils)od invocation.                 Dump files in octal, etc.
* paste: (coreutils)paste invocation.           Merge lines of files.
* pathchk: (coreutils)pathchk invocation.       Check file name portability.
* pr: (coreutils)pr invocation.                 Paginate or columnate files.
* printenv: (coreutils)printenv invocation.     Print environment variables.
* printf: (coreutils)printf invocation.         Format and print data.
* ptx: (coreutils)ptx invocation.               Produce permuted indexes.
* pwd: (coreutils)pwd invocation.               Print working directory.
* readlink: (coreutils)readlink invocation.     Print referent of a symlink.
* realpath: (coreutils)realpath invocation.     Print resolved file names.
* rm: (coreutils)rm invocation.                 Remove files.
* rmdir: (coreutils)rmdir invocation.           Remove empty directories.
* runcon: (coreutils)runcon invocation.         Run in specified SELinux CTX.
* seq: (coreutils)seq invocation.               Print numeric sequences
* sha1sum: (coreutils)sha1sum invocation.       Print or check SHA-1 digests.
* sha2: (coreutils)sha2 utilities.              Print or check SHA-2 digests.
* shred: (coreutils)shred invocation.           Remove files more securely.
* shuf: (coreutils)shuf invocation.             Shuffling text files.
* sleep: (coreutils)sleep invocation.           Delay for a specified time.
* sort: (coreutils)sort invocation.             Sort text files.
* split: (coreutils)split invocation.           Split into pieces.
* stat: (coreutils)stat invocation.             Report file(system) status.
* stdbuf: (coreutils)stdbuf invocation.         Modify stdio buffering.
* stty: (coreutils)stty invocation.             Print/change terminal settings.
* sum: (coreutils)sum invocation.               Print traditional checksum.
* sync: (coreutils)sync invocation.             Synchronize memory to disk.
* tac: (coreutils)tac invocation.               Reverse files.
* tail: (coreutils)tail invocation.             Output the last part of files.
* tee: (coreutils)tee invocation.               Redirect to multiple files.
* test: (coreutils)test invocation.             File/string tests.
* timeout: (coreutils)timeout invocation.       Run with time limit.
* touch: (coreutils)touch invocation.           Change file timestamps.
* tr: (coreutils)tr invocation.                 Translate characters.
* true: (coreutils)true invocation.             Do nothing, successfully.
* truncate: (coreutils)truncate invocation.     Shrink/extend size of a file.
* tsort: (coreutils)tsort invocation.           Topological sort.
* tty: (coreutils)tty invocation.               Print terminal name.
* uname: (coreutils)uname invocation.           Print system information.
* unexpand: (coreutils)unexpand invocation.     Convert spaces to tabs.
* uniq: (coreutils)uniq invocation.             Uniquify files.
* unlink: (coreutils)unlink invocation.         Removal via unlink(2).
* uptime: (coreutils)uptime invocation.         Print uptime and load.
* users: (coreutils)users invocation.           Print current user names.
* vdir: (coreutils)vdir invocation.             List directories verbosely.
* wc: (coreutils)wc invocation.                 Line, word, and byte counts.
* who: (coreutils)who invocation.               Print who is logged in.
* whoami: (coreutils)whoami invocation.         Print effective user ID.
* yes: (coreutils)yes invocation.               Print a string indefinitely.
@end direntry

@copying
This manual documents version @value{VERSION} of the GNU core
utilities, including the standard programs for text and file manipulation.

Copyright @copyright{} 1994-2016 Free Software Foundation, Inc.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts.  A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
@end quotation
@end copying

@titlepage
@title GNU @code{Coreutils}
@subtitle Core GNU utilities
@subtitle for version @value{VERSION}, @value{UPDATED}
@author David MacKenzie et al.

@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage
@shortcontents
@contents

@ifnottex
@node Top
@top GNU Coreutils

@insertcopying
@end ifnottex

@cindex core utilities
@cindex text utilities
@cindex shell utilities
@cindex file utilities

@menu
* Introduction::                 Caveats, overview, and authors
* Common options::               Common options
* Output of entire files::       cat tac nl od base32 base64
* Formatting file contents::     fmt pr fold
* Output of parts of files::     head tail split csplit
* Summarizing files::            wc sum cksum md5sum sha1sum sha2
* Operating on sorted files::    sort shuf uniq comm ptx tsort
* Operating on fields::          cut paste join
* Operating on characters::      tr expand unexpand
* Directory listing::            ls dir vdir dircolors
* Basic operations::             cp dd install mv rm shred
* Special file types::         mkdir rmdir unlink mkfifo mknod ln link readlink
* Changing file attributes::     chgrp chmod chown touch
* Disk usage::                   df du stat sync truncate
* Printing text::                echo printf yes
* Conditions::                   false true test expr
* Redirection::                  tee
* File name manipulation::       dirname basename pathchk mktemp realpath
* Working context::              pwd stty printenv tty
* User information::             id logname whoami groups users who
* System context::               date arch nproc uname hostname hostid uptime
* SELinux context::              chcon runcon
* Modified command invocation::  chroot env nice nohup stdbuf timeout
* Process control::              kill
* Delaying::                     sleep
* Numeric operations::           factor numfmt seq
* File permissions::             Access modes
* Date input formats::           Specifying date strings
* Opening the software toolbox:: The software tools philosophy
* GNU Free Documentation License:: Copying and sharing this manual
* Concept index::                General index

@detailmenu
 --- The Detailed Node Listing ---

Common Options

* Exit status::                  Indicating program success or failure
* Backup options::               Backup options
* Block size::                   Block size
* Floating point::               Floating point number representation
* Signal specifications::        Specifying signals
* Disambiguating names and IDs:: chgrp, chown, chroot, id: user and group syntax
* Random sources::               Sources of random data
* Target directory::             Target directory
* Trailing slashes::             Trailing slashes
* Traversing symlinks::          Traversing symlinks to directories
* Treating / specially::         Treating / specially
* Standards conformance::        Standards conformance
* Multi-call invocation::        Multi-call program invocation

Output of entire files

* cat invocation::               Concatenate and write files
* tac invocation::               Concatenate and write files in reverse
* nl invocation::                Number lines and write files
* od invocation::                Write files in octal or other formats
* base32 invocation::            Transform data into printable data
* base64 invocation::            Transform data into printable data

Formatting file contents

* fmt invocation::               Reformat paragraph text
* pr invocation::                Paginate or columnate files for printing
* fold invocation::              Wrap input lines to fit in specified width

Output of parts of files

* head invocation::              Output the first part of files
* tail invocation::              Output the last part of files
* split invocation::             Split a file into fixed-size pieces
* csplit invocation::            Split a file into context-determined pieces

Summarizing files

* wc invocation::                Print newline, word, and byte counts
* sum invocation::               Print checksum and block counts
* cksum invocation::             Print CRC checksum and byte counts
* md5sum invocation::            Print or check MD5 digests
* sha1sum invocation::           Print or check SHA-1 digests
* sha2 utilities::               Print or check SHA-2 digests

Operating on sorted files

* sort invocation::              Sort text files
* shuf invocation::              Shuffle text files
* uniq invocation::              Uniquify files
* comm invocation::              Compare two sorted files line by line
* ptx invocation::               Produce a permuted index of file contents
* tsort invocation::             Topological sort

@command{ptx}: Produce permuted indexes

* General options in ptx::       Options which affect general program behavior
* Charset selection in ptx::     Underlying character set considerations
* Input processing in ptx::      Input fields, contexts, and keyword selection
* Output formatting in ptx::     Types of output format, and sizing the fields
* Compatibility in ptx::         The GNU extensions to @command{ptx}

Operating on fields

* cut invocation::               Print selected parts of lines
* paste invocation::             Merge lines of files
* join invocation::              Join lines on a common field

Operating on characters

* tr invocation::                Translate, squeeze, and/or delete characters
* expand invocation::            Convert tabs to spaces
* unexpand invocation::          Convert spaces to tabs

@command{tr}: Translate, squeeze, and/or delete characters

* Character sets::               Specifying sets of characters
* Translating::                  Changing one set of characters to another
* Squeezing and deleting::       Removing characters

Directory listing

* ls invocation::                List directory contents
* dir invocation::               Briefly list directory contents
* vdir invocation::              Verbosely list directory contents
* dircolors invocation::         Color setup for @command{ls}

@command{ls}:  List directory contents

* Which files are listed::       Which files are listed
* What information is listed::   What information is listed
* Sorting the output::           Sorting the output
* Details about version sort::   More details about version sort
* General output formatting::    General output formatting
* Formatting the file names::    Formatting the file names

Basic operations

* cp invocation::                Copy files and directories
* dd invocation::                Convert and copy a file
* install invocation::           Copy files and set attributes
* mv invocation::                Move (rename) files
* rm invocation::                Remove files or directories
* shred invocation::             Remove files more securely

Special file types

* link invocation::              Make a hard link via the link syscall
* ln invocation::                Make links between files
* mkdir invocation::             Make directories
* mkfifo invocation::            Make FIFOs (named pipes)
* mknod invocation::             Make block or character special files
* readlink invocation::          Print value of a symlink or canonical file name
* rmdir invocation::             Remove empty directories
* unlink invocation::            Remove files via unlink syscall

Changing file attributes

* chown invocation::             Change file owner and group
* chgrp invocation::             Change group ownership
* chmod invocation::             Change access permissions
* touch invocation::             Change file timestamps

Disk usage

* df invocation::                Report file system disk space usage
* du invocation::                Estimate file space usage
* stat invocation::              Report file or file system status
* sync invocation::              Synchronize cached writes to persistent storage
* truncate invocation::          Shrink or extend the size of a file

Printing text

* echo invocation::              Print a line of text
* printf invocation::            Format and print data
* yes invocation::               Print a string until interrupted

Conditions

* false invocation::             Do nothing, unsuccessfully
* true invocation::              Do nothing, successfully
* test invocation::              Check file types and compare values
* expr invocation::              Evaluate expressions

@command{test}: Check file types and compare values

* File type tests::              File type tests
* Access permission tests::      Access permission tests
* File characteristic tests::    File characteristic tests
* String tests::                 String tests
* Numeric tests::                Numeric tests

@command{expr}: Evaluate expression

* String expressions::           + : match substr index length
* Numeric expressions::          + - * / %
* Relations for expr::           | & < <= = == != >= >
* Examples of expr::             Examples of using @command{expr}

Redirection

* tee invocation::               Redirect output to multiple files or processes

File name manipulation

* basename invocation::          Strip directory and suffix from a file name
* dirname invocation::           Strip last file name component
* pathchk invocation::           Check file name validity and portability
* mktemp invocation::            Create temporary file or directory
* realpath invocation::          Print resolved file names

Working context

* pwd invocation::               Print working directory
* stty invocation::              Print or change terminal characteristics
* printenv invocation::          Print all or some environment variables
* tty invocation::               Print file name of terminal on standard input

@command{stty}: Print or change terminal characteristics

* Control::                      Control settings
* Input::                        Input settings
* Output::                       Output settings
* Local::                        Local settings
* Combination::                  Combination settings
* Characters::                   Special characters
* Special::                      Special settings

User information

* id invocation::                Print user identity
* logname invocation::           Print current login name
* whoami invocation::            Print effective user ID
* groups invocation::            Print group names a user is in
* users invocation::             Print login names of users currently logged in
* who invocation::               Print who is currently logged in

System context

* arch invocation::              Print machine hardware name
* date invocation::              Print or set system date and time
* nproc invocation::             Print the number of processors
* uname invocation::             Print system information
* hostname invocation::          Print or set system name
* hostid invocation::            Print numeric host identifier
* uptime invocation::            Print system uptime and load

@command{date}: Print or set system date and time

* Time conversion specifiers::   %[HIklMNpPrRsSTXzZ]
* Date conversion specifiers::   %[aAbBcCdDeFgGhjmuUVwWxyY]
* Literal conversion specifiers:: %[%nt]
* Padding and other flags::      Pad with zeros, spaces, etc.
* Setting the time::             Changing the system clock
* Options for date::             Instead of the current time
* Date input formats::           Specifying date strings
* Examples of date::             Examples

SELinux context

* chcon invocation::             Change SELinux context of file
* runcon invocation::            Run a command in specified SELinux context

Modified command invocation

* chroot invocation::            Run a command with a different root directory
* env invocation::               Run a command in a modified environment
* nice invocation::              Run a command with modified niceness
* nohup invocation::             Run a command immune to hangups
* stdbuf invocation::            Run a command with modified I/O buffering
* timeout invocation::           Run a command with a time limit

Process control

* kill invocation::              Sending a signal to processes.

Delaying

* sleep invocation::             Delay for a specified time

Numeric operations

* factor invocation::            Print prime factors
* numfmt invocation::            Reformat numbers
* seq invocation::               Print numeric sequences

File permissions

* Mode Structure::               Structure of file mode bits
* Symbolic Modes::               Mnemonic representation of file mode bits
* Numeric Modes::                File mode bits as octal numbers
* Directory Setuid and Setgid::  Set-user-ID and set-group-ID on directories

Date input formats

* General date syntax::          Common rules
* Calendar date items::          19 Dec 1994
* Time of day items::            9:20pm
* Time zone items::              EST, PDT, UTC, @dots{}
* Combined date and time of day items:: 1972-09-24T20:02:00,000000-0500
* Day of week items::            Monday and others
* Relative items in date strings:: next tuesday, 2 years ago
* Pure numbers in date strings:: 19931219, 1440
* Seconds since the Epoch::      @@1078100502
* Specifying time zone rules::   TZ="America/New_York", TZ="UTC0"
* Authors of parse_datetime::    Bellovin, Eggert, Salz, Berets, et al.

Opening the software toolbox

* Toolbox introduction::         Toolbox introduction
* I/O redirection::              I/O redirection
* The who command::              The @command{who} command
* The cut command::              The @command{cut} command
* The sort command::             The @command{sort} command
* The uniq command::             The @command{uniq} command
* Putting the tools together::   Putting the tools together

Copying This Manual

* GNU Free Documentation License::     Copying and sharing this manual

@end detailmenu
@end menu


@node Introduction
@chapter Introduction

This manual is a work in progress: many sections make no attempt to explain
basic concepts in a way suitable for novices.  Thus, if you are interested,
please get involved in improving this manual.  The entire GNU community
will benefit.

@cindex POSIX
The GNU utilities documented here are mostly compatible with the
POSIX standard.
@cindex bugs, reporting

Please report bugs to @email{bug-coreutils@@gnu.org}.
Include the version number, machine architecture, input files, and
any other information needed to reproduce the bug: your input, what you
expected, what you got, and why it is wrong.

If you have a problem with @command{sort}, try running @samp{sort
--debug}, as it can can often help find and fix problems without
having to wait for an answer to a bug report.  If the debug output
does not suffice to fix the problem on your own, please compress and
attach it to the rest of your bug report.

Although diffs are welcome,
please include a description of the problem as well, since this is
sometimes difficult to infer.  @xref{Bugs, , , gcc, Using and Porting GNU CC}.

@cindex Berry, K.
@cindex Paterson, R.
@cindex Stallman, R.
@cindex Pinard, F.
@cindex MacKenzie, D.
@cindex Meyering, J.
@cindex Youmans, B.
This manual was originally derived from the Unix man pages in the
distributions, which were written by David MacKenzie and updated by Jim
Meyering.  What you are reading now is the authoritative documentation
for these utilities; the man pages are no longer being maintained.  The
original @command{fmt} man page was written by Ross Paterson.  Fran@,{c}ois
Pinard did the initial conversion to Texinfo format.  Karl Berry did the
indexing, some reorganization, and editing of the results.  Brian
Youmans of the Free Software Foundation office staff combined the
manuals for textutils, fileutils, and sh-utils to produce the present
omnibus manual.  Richard Stallman contributed his usual invaluable
insights to the overall process.

@node Common options
@chapter Common options

@macro optBackup
@item -b
@itemx --backup[=@var{method}]
@opindex -b
@opindex --backup
@vindex VERSION_CONTROL
@cindex backups, making
@xref{Backup options}.
Make a backup of each file that would otherwise be overwritten or removed.
@end macro

@macro optBackupSuffix
@item -S @var{suffix}
@itemx --suffix=@var{suffix}
@opindex -S
@opindex --suffix
Append @var{suffix} to each backup file made with @option{-b}.
@xref{Backup options}.
@end macro

@macro optTargetDirectory
@item -t @var{directory}
@itemx --target-directory=@var{directory}
@opindex -t
@opindex --target-directory
@cindex target directory
@cindex destination directory
Specify the destination @var{directory}.
@xref{Target directory}.
@end macro

@macro optNoTargetDirectory
@item -T
@itemx --no-target-directory
@opindex -T
@opindex --no-target-directory
@cindex target directory
@cindex destination directory
Do not treat the last operand specially when it is a directory or a
symbolic link to a directory.  @xref{Target directory}.
@end macro

@macro outputNUL
@cindex output NUL-byte-terminated lines
Output a zero byte (ASCII NUL) at the end of each line,
rather than a newline.  This option enables other programs to parse the
output even when that output would contain data with embedded newlines.
@end macro

@macro optNull
@item -0
@itemx --null
@opindex -0
@opindex --null
@outputNUL
@end macro

@macro optZero
@item -z
@itemx --zero
@opindex -z
@opindex --zero
@outputNUL
@end macro

@macro optZeroTerminated
@item -z
@itemx --zero-terminated
@opindex -z
@opindex --zero-terminated
@cindex process zero-terminated items
Delimit items with a zero byte rather than a newline (ASCII LF).
I.e., treat input as items separated by ASCII NUL
and terminate output items with ASCII NUL.
This option can be useful in conjunction with @samp{perl -0} or
@samp{find -print0} and @samp{xargs -0} which do the same in order to
reliably handle arbitrary file names (even those containing blanks
or other special characters).
@end macro

@macro optSi
@item --si
@opindex --si
@cindex SI output
Append an SI-style abbreviation to each size, such as @samp{M} for
megabytes.  Powers of 1000 are used, not 1024; @samp{M} stands for
1,000,000 bytes.  This option is equivalent to
@option{--block-size=si}.  Use the @option{-h} or
@option{--human-readable} option if
you prefer powers of 1024.
@end macro

@macro optHumanReadable
@item -h
@itemx --human-readable
@opindex -h
@opindex --human-readable
@cindex human-readable output
Append a size letter to each size, such as @samp{M} for mebibytes.
Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
This option is equivalent to @option{--block-size=human-readable}.
Use the @option{--si} option if you prefer powers of 1000.
@end macro

@macro optStripTrailingSlashes
@item --strip-trailing-slashes
@opindex --strip-trailing-slashes
@cindex stripping trailing slashes
Remove any trailing slashes from each @var{source} argument.
@xref{Trailing slashes}.
@end macro

@macro mayConflictWithShellBuiltIn{cmd}
@cindex conflicts with shell built-ins
@cindex built-in shell commands, conflicts with
Due to shell aliases and built-in @command{\cmd\} functions, using an
unadorned @command{\cmd\} interactively or in a script may get you
different functionality than that described here.  Invoke it via
@command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
from the shell.

@end macro

@macro multiplierSuffixes{varName}
@var{\varName\} may be, or may be an integer optionally followed by,
one of the following multiplicative suffixes:
@example
@samp{b}  =>            512 ("blocks")
@samp{KB} =>           1000 (KiloBytes)
@samp{K}  =>           1024 (KibiBytes)
@samp{MB} =>      1000*1000 (MegaBytes)
@samp{M}  =>      1024*1024 (MebiBytes)
@samp{GB} => 1000*1000*1000 (GigaBytes)
@samp{G}  => 1024*1024*1024 (GibiBytes)
@end example
and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
@end macro

@c FIXME: same as above, but no ``blocks'' line.
@macro multiplierSuffixesNoBlocks{varName}
@var{\varName\} may be, or may be an integer optionally followed by,
one of the following multiplicative suffixes:
@example
@samp{KB} =>           1000 (KiloBytes)
@samp{K}  =>           1024 (KibiBytes)
@samp{MB} =>      1000*1000 (MegaBytes)
@samp{M}  =>      1024*1024 (MebiBytes)
@samp{GB} => 1000*1000*1000 (GigaBytes)
@samp{G}  => 1024*1024*1024 (GibiBytes)
@end example
and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
@end macro

@cindex common options

Certain options are available in all of these programs.  Rather than
writing identical descriptions for each of the programs, they are
described here.  (In fact, every GNU program accepts (or should accept)
these options.)

@vindex POSIXLY_CORRECT
Normally options and operands can appear in any order, and programs act
as if all the options appear before any operands.  For example,
@samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
@samp{:} is an option-argument of @option{-t}.  However, if the
@env{POSIXLY_CORRECT} environment variable is set, options must appear
before operands, unless otherwise specified for a particular command.

A few programs can usefully have trailing operands with leading
@samp{-}.  With such a program, options must precede operands even if
@env{POSIXLY_CORRECT} is not set, and this fact is noted in the
program description.  For example, the @command{env} command's options
must appear before its operands, since in some cases the operands
specify a command that itself contains options.

Most programs that accept long options recognize unambiguous
abbreviations of those options.  For example, @samp{rmdir
--ignore-fail-on-non-empty} can be invoked as @samp{rmdir
--ignore-fail} or even @samp{rmdir --i}.  Ambiguous options, such as
@samp{ls --h}, are identified as such.

Some of these programs recognize the @option{--help} and @option{--version}
options only when one of them is the sole command line argument.  For
these programs, abbreviations of the long options are not always recognized.

@table @samp

@item --help
@opindex --help
@cindex help, online
Print a usage message listing all available options, then exit successfully.

@item --version
@opindex --version
@cindex version number, finding
Print the version number, then exit successfully.

@item --
@opindex --
@cindex option delimiter
Delimit the option list.  Later arguments, if any, are treated as
operands even if they begin with @samp{-}.  For example, @samp{sort --
-r} reads from the file named @file{-r}.

@end table

@cindex standard input
@cindex standard output
A single @samp{-} operand is not really an option, though it looks like one.  It
stands for a file operand, and some tools treat it as standard input, or as
standard output if that is clear from the context.  For example, @samp{sort -}
reads from standard input, and is equivalent to plain @samp{sort}.  Unless
otherwise specified, a @samp{-} can appear as any operand that requires a file
name.

@menu
* Exit status::                 Indicating program success or failure.
* Backup options::              -b -S, in some programs.
* Block size::                  BLOCK_SIZE and --block-size, in some programs.
* Floating point::              Floating point number representation.
* Signal specifications::       Specifying signals using the --signal option.
* Disambiguating names and IDs:: chgrp, chown, chroot, id: user and group syntax
* Random sources::              --random-source, in some programs.
* Target directory::            Specifying a target directory, in some programs.
* Trailing slashes::            --strip-trailing-slashes, in some programs.
* Traversing symlinks::         -H, -L, or -P, in some programs.
* Treating / specially::        --preserve-root and --no-preserve-root.
* Special built-in utilities::  @command{break}, @command{:}, @dots{}
* Standards conformance::       Conformance to the POSIX standard.
* Multi-call invocation::       Multi-call program invocation.
@end menu


@node Exit status
@section Exit status

@macro exitstatus
An exit status of zero indicates success,
and a nonzero value indicates failure.
@end macro

Nearly every command invocation yields an integral @dfn{exit status}
that can be used to change how other commands work.
For the vast majority of commands, an exit status of zero indicates
success.  Failure is indicated by a nonzero value---typically
@samp{1}, though it may differ on unusual platforms as POSIX
requires only that it be nonzero.

However, some of the programs documented here do produce
other exit status values and a few associate different
meanings with the values @samp{0} and @samp{1}.
Here are some of the exceptions:
@command{chroot}, @command{env}, @command{expr}, @command{nice},
@command{nohup}, @command{numfmt}, @command{printenv}, @command{sort},
@command{stdbuf}, @command{test}, @command{timeout}, @command{tty}.


@node Backup options
@section Backup options

@cindex backup options

Some GNU programs (at least @command{cp}, @command{install},
@command{ln}, and @command{mv}) optionally make backups of files
before writing new versions.
These options control the details of these backups.  The options are also
briefly mentioned in the descriptions of the particular programs.

@table @samp

@item -b
@itemx --backup[=@var{method}]
@opindex -b
@opindex --backup
@vindex VERSION_CONTROL
@cindex backups, making
Make a backup of each file that would otherwise be overwritten or removed.
Without this option, the original versions are destroyed.
Use @var{method} to determine the type of backups to make.
When this option is used but @var{method} is not specified,
then the value of the @env{VERSION_CONTROL}
environment variable is used.  And if @env{VERSION_CONTROL} is not set,
the default backup type is @samp{existing}.

Note that the short form of this option, @option{-b} does not accept any
argument.  Using @option{-b} is equivalent to using @option{--backup=existing}.

@vindex version-control @r{Emacs variable}
This option corresponds to the Emacs variable @samp{version-control};
the values for @var{method} are the same as those used in Emacs.
This option also accepts more descriptive names.
The valid @var{method}s are (unique abbreviations are accepted):

@table @samp
@item none
@itemx off
@opindex none @r{backup method}
Never make backups.

@item numbered
@itemx t
@opindex numbered @r{backup method}
Always make numbered backups.

@item existing
@itemx nil
@opindex existing @r{backup method}
Make numbered backups of files that already have them, simple backups
of the others.

@item simple
@itemx never
@opindex simple @r{backup method}
Always make simple backups.  Please note @samp{never} is not to be
confused with @samp{none}.

@end table

@item -S @var{suffix}
@itemx --suffix=@var{suffix}
@opindex -S
@opindex --suffix
@cindex backup suffix
@vindex SIMPLE_BACKUP_SUFFIX
Append @var{suffix} to each backup file made with @option{-b}.  If this
option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
environment variable is used.  And if @env{SIMPLE_BACKUP_SUFFIX} is not
set, the default is @samp{~}, just as in Emacs.

@end table

@node Block size
@section Block size

@cindex block size

Some GNU programs (at least @command{df}, @command{du}, and
@command{ls}) display sizes in ``blocks''.  You can adjust the block size
and method of display to make sizes easier to read.  The block size
used for display is independent of any file system block size.
Fractional block counts are rounded up to the nearest integer.

@opindex --block-size=@var{size}
@vindex BLOCKSIZE
@vindex BLOCK_SIZE
@vindex DF_BLOCK_SIZE
@vindex DU_BLOCK_SIZE
@vindex LS_BLOCK_SIZE
@vindex POSIXLY_CORRECT@r{, and block size}

The default block size is chosen by examining the following environment
variables in turn; the first one that is set determines the block size.

@table @code

@item DF_BLOCK_SIZE
This specifies the default block size for the @command{df} command.
Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
@env{LS_BLOCK_SIZE} for @command{ls}.

@item BLOCK_SIZE
This specifies the default block size for all three commands, if the
above command-specific environment variables are not set.

@item BLOCKSIZE
This specifies the default block size for all values that are normally
printed as blocks, if neither @env{BLOCK_SIZE} nor the above
command-specific environment variables are set.  Unlike the other
environment variables, @env{BLOCKSIZE} does not affect values that are
normally printed as byte counts, e.g., the file sizes contained in
@code{ls -l} output.

@item POSIXLY_CORRECT
If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
@env{BLOCKSIZE} is set, but this variable is set, the block size
defaults to 512.

@end table

If none of the above environment variables are set, the block size
currently defaults to 1024 bytes in most contexts, but this number may
change in the future.  For @command{ls} file sizes, the block size
defaults to 1 byte.

@cindex human-readable output
@cindex SI output

A block size specification can be a positive integer specifying the number
of bytes per block, or it can be @code{human-readable} or @code{si} to
select a human-readable format.  Integers may be followed by suffixes
that are upward compatible with the
@uref{http://www.bipm.org/en/publications/si-brochure/chapter3.html,
SI prefixes}
for decimal multiples and with the
@uref{http://physics.nist.gov/cuu/Units/binary.html, ISO/IEC 80000-13
(formerly IEC 60027-2) prefixes} for binary multiples.

With human-readable formats, output sizes are followed by a size letter
such as @samp{M} for megabytes.  @code{BLOCK_SIZE=human-readable} uses
powers of 1024; @samp{M} stands for 1,048,576 bytes.
@code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
@samp{B}; @samp{MB} stands for 1,000,000 bytes.

@vindex LC_NUMERIC
A block size specification preceded by @samp{'} causes output sizes to
be displayed with thousands separators.  The @env{LC_NUMERIC} locale
specifies the thousands separator and grouping.  For example, in an
American English locale, @samp{--block-size="'1kB"} would cause a size
of 1234000 bytes to be displayed as @samp{1,234}.  In the default C
locale, there is no thousands separator so a leading @samp{'} has no
effect.

An integer block size can be followed by a suffix to specify a
multiple of that size.  A bare size letter,
or one followed by @samp{iB}, specifies
a multiple using powers of 1024.  A size letter followed by @samp{B}
specifies powers of 1000 instead.  For example, @samp{1M} and
@samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
equivalent to @samp{1000000}.

A plain suffix without a preceding integer acts as if @samp{1} were
prepended, except that it causes a size indication to be appended to
the output.  For example, @samp{--block-size="kB"} displays 3000 as
@samp{3kB}.

The following suffixes are defined.  Large sizes like @code{1Y}
may be rejected by your computer due to limitations of its arithmetic.

@table @samp
@item kB
@cindex kilobyte, definition of
kilobyte: @math{10^3 = 1000}.
@item k
@itemx K
@itemx KiB
@cindex kibibyte, definition of
kibibyte: @math{2^{10} = 1024}.  @samp{K} is special: the SI prefix is
@samp{k} and the ISO/IEC 80000-13 prefix is @samp{Ki}, but tradition and
POSIX use @samp{k} to mean @samp{KiB}.
@item MB
@cindex megabyte, definition of
megabyte: @math{10^6 = 1,000,000}.
@item M
@itemx MiB
@cindex mebibyte, definition of
mebibyte: @math{2^{20} = 1,048,576}.
@item GB
@cindex gigabyte, definition of
gigabyte: @math{10^9 = 1,000,000,000}.
@item G
@itemx GiB
@cindex gibibyte, definition of
gibibyte: @math{2^{30} = 1,073,741,824}.
@item TB
@cindex terabyte, definition of
terabyte:  @math{10^{12} = 1,000,000,000,000}.
@item T
@itemx TiB
@cindex tebibyte, definition of
tebibyte: @math{2^{40} = 1,099,511,627,776}.
@item PB
@cindex petabyte, definition of
petabyte: @math{10^{15} = 1,000,000,000,000,000}.
@item P
@itemx PiB
@cindex pebibyte, definition of
pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
@item EB
@cindex exabyte, definition of
exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
@item E
@itemx EiB
@cindex exbibyte, definition of
exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
@item ZB
@cindex zettabyte, definition of
zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
@item Z
@itemx ZiB
@math{2^{70} = 1,180,591,620,717,411,303,424}.
@item YB
@cindex yottabyte, definition of
yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
@item Y
@itemx YiB
@math{2^{80} = 1,208,925,819,614,629,174,706,176}.
@end table

@opindex -k
@opindex -h
@opindex --block-size
@opindex --human-readable
@opindex --si

Block size defaults can be overridden by an explicit
@option{--block-size=@var{size}} option.  The @option{-k}
option is equivalent to @option{--block-size=1K}, which
is the default unless the @env{POSIXLY_CORRECT} environment variable is
set.  The @option{-h} or @option{--human-readable} option is equivalent to
@option{--block-size=human-readable}.  The @option{--si} option is
equivalent to @option{--block-size=si}.  Note for @command{ls}
the @option{-k} option does not control the display of the
apparent file sizes, whereas the @option{--block-size} option does.

@node Floating point
@section Floating point numbers
@cindex floating point
@cindex IEEE floating point

Commands that accept or produce floating point numbers employ the
floating point representation of the underlying system, and suffer
from rounding error, overflow, and similar floating-point issues.
Almost all modern systems use IEEE-754 floating point, and it is
typically portable to assume IEEE-754 behavior these days.  IEEE-754
has positive and negative infinity, distinguishes positive from
negative zero, and uses special values called NaNs to represent
invalid computations such as dividing zero by itself.  For more
information, please see David Goldberg's paper
@uref{http://@/www.validlab.com/@/goldberg/@/paper.pdf, What Every
Computer Scientist Should Know About Floating-Point Arithmetic}.

@vindex LC_NUMERIC
Commands that accept floating point numbers as options, operands or
input use the standard C functions @code{strtod} and @code{strtold} to
convert from text to floating point numbers.  These floating point
numbers therefore can use scientific notation like @code{1.0e-34} and
@code{-10e100}.  Commands that parse floating point also understand
case-insensitive @code{inf}, @code{infinity}, and @code{NaN}, although
whether such values are useful depends on the command in question.
Modern C implementations also accept hexadecimal floating point
numbers such as @code{-0x.ep-3}, which stands for @minus{}14/16 times
@math{2^-3}, which equals @minus{}0.109375.  The @env{LC_NUMERIC}
locale determines the decimal-point character.  @xref{Parsing of
Floats,,, libc, The GNU C Library Reference Manual}.

@node Signal specifications
@section Signal specifications
@cindex signals, specifying

A @var{signal} may be a signal name like @samp{HUP}, or a signal
number like @samp{1}, or an exit status of a process terminated by the
signal.  A signal name can be given in canonical form or prefixed by
@samp{SIG}@.  The case of the letters is ignored.  The following signal names
and numbers are supported on all POSIX compliant systems:

@table @samp
@item HUP
1.  Hangup.
@item INT
2.  Terminal interrupt.
@item QUIT
3.  Terminal quit.
@item ABRT
6.  Process abort.
@item KILL
9.  Kill (cannot be caught or ignored).
@item ALRM
14.  Alarm Clock.
@item TERM
15.  Termination.
@end table

@noindent
Other supported signal names have system-dependent corresponding
numbers.  All systems conforming to POSIX 1003.1-2001 also
support the following signals:

@table @samp
@item BUS
Access to an undefined portion of a memory object.
@item CHLD
Child process terminated, stopped, or continued.
@item CONT
Continue executing, if stopped.
@item FPE
Erroneous arithmetic operation.
@item ILL
Illegal Instruction.
@item PIPE
Write on a pipe with no one to read it.
@item SEGV
Invalid memory reference.
@item STOP
Stop executing (cannot be caught or ignored).
@item TSTP
Terminal stop.
@item TTIN
Background process attempting read.
@item TTOU
Background process attempting write.
@item URG
High bandwidth data is available at a socket.
@item USR1
User-defined signal 1.
@item USR2
User-defined signal 2.
@end table

@noindent
POSIX 1003.1-2001 systems that support the XSI extension
also support the following signals:

@table @samp
@item POLL
Pollable event.
@item PROF
Profiling timer expired.
@item SYS
Bad system call.
@item TRAP
Trace/breakpoint trap.
@item VTALRM
Virtual timer expired.
@item XCPU
CPU time limit exceeded.
@item XFSZ
File size limit exceeded.
@end table

@noindent
POSIX 1003.1-2001 systems that support the XRT extension
also support at least eight real-time signals called @samp{RTMIN},
@samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.

@node Disambiguating names and IDs
@section chown, chgrp, chroot, id: Disambiguating user names and IDs
@cindex user names, disambiguating
@cindex user IDs, disambiguating
@cindex group names, disambiguating
@cindex group IDs, disambiguating
@cindex disambiguating group names and IDs

Since the @var{user} and @var{group} arguments to these commands
may be specified as names or numeric IDs, there is an
apparent ambiguity.
What if a user or group @emph{name} is a string of digits?
@footnote{Using a number as a user name is common in some environments.}
Should the command interpret it as a user name or as an ID@?
POSIX requires that these commands
first attempt to resolve the specified string as a name, and
only once that fails, then try to interpret it as an ID@.
This is troublesome when you want to specify a numeric ID, say 42,
and it must work even in a pathological situation where
@samp{42} is a user name that maps to some other user ID, say 1000.
Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1000---not what you intended.

GNU @command{chown}, @command{chgrp}, @command{chroot}, and @command{id}
provide a way to work around this, that at the same time may result in a
significant performance improvement by eliminating a database look-up.
Simply precede each numeric user ID and/or group ID with a @samp{+},
in order to force its interpretation as an integer:

@example
chown +42 F
chgrp +$numeric_group_id another-file
chown +0:+0 /
@end example

The name look-up process is skipped for each @samp{+}-prefixed string,
because a string containing @samp{+} is never a valid user or group name.
This syntax is accepted on most common Unix systems, but not on Solaris 10.

@node Random sources
@section Sources of random data

@cindex random sources

The @command{shuf}, @command{shred}, and @command{sort} commands
sometimes need random data to do their work.  For example, @samp{sort
-R} must choose a hash function at random, and it needs random data to
make this selection.

By default these commands use an internal pseudo-random generator
initialized by a small amount of entropy, but can be directed to use
an external source with the @option{--random-source=@var{file}} option.
An error is reported if @var{file} does not contain enough bytes.

For example, the device file @file{/dev/urandom} could be used as the
source of random data.  Typically, this device gathers environmental
noise from device drivers and other sources into an entropy pool, and
uses the pool to generate random bits.  If the pool is short of data,
the device reuses the internal pool to produce more bits, using a
cryptographically secure pseudo-random number generator.  But be aware
that this device is not designed for bulk random data generation
and is relatively slow.

@file{/dev/urandom} suffices for most practical uses, but applications
requiring high-value or long-term protection of private data may
require an alternate data source like @file{/dev/random} or
@file{/dev/arandom}.  The set of available sources depends on your
operating system.

To reproduce the results of an earlier invocation of a command, you
can save some random data into a file and then use that file as the
random source in earlier and later invocations of the command.
@cindex random seed
Rather than depending on a file, one can generate a reproducible
arbitrary amount of pseudo-random data given a seed value, using
for example:

@example
get_seeded_random()
@{
  seed="$1"
  openssl enc -aes-256-ctr -pass pass:"$seed" -nosalt \
    </dev/zero 2>/dev/null
@}

shuf -i1-100 --random-source=<(get_seeded_random 42)
@end example

@node Target directory
@section Target directory

@cindex target directory

The @command{cp}, @command{install}, @command{ln}, and @command{mv}
commands normally treat the last operand specially when it is a
directory or a symbolic link to a directory.  For example, @samp{cp
source dest} is equivalent to @samp{cp source dest/source} if
@file{dest} is a directory.  Sometimes this behavior is not exactly
what is wanted, so these commands support the following options to
allow more fine-grained control:

@table @samp

@item -T
@itemx --no-target-directory
@opindex --no-target-directory
@cindex target directory
@cindex destination directory
Do not treat the last operand specially when it is a directory or a
symbolic link to a directory.  This can help avoid race conditions in
programs that operate in a shared area.  For example, when the command
@samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
@file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
renamed to @file{/tmp/dest/source} instead, if some other process
created @file{/tmp/dest} as a directory.  However, if @file{mv
-T /tmp/source /tmp/dest} succeeds, there is no
question that @file{/tmp/source} was renamed to @file{/tmp/dest}.

In the opposite situation, where you want the last operand to be
treated as a directory and want a diagnostic otherwise, you can use
the @option{--target-directory} (@option{-t}) option.

@item -t @var{directory}
@itemx --target-directory=@var{directory}
@opindex --target-directory
@cindex target directory
@cindex destination directory
Use @var{directory} as the directory component of each destination
file name.

The interface for most programs is that after processing options and a
finite (possibly zero) number of fixed-position arguments, the remaining
argument list is either expected to be empty, or is a list of items
(usually files) that will all be handled identically.  The @command{xargs}
program is designed to work well with this convention.

The commands in the @command{mv}-family are unusual in that they take
a variable number of arguments with a special case at the @emph{end}
(namely, the target directory).  This makes it nontrivial to perform some
operations, e.g., ``move all files from here to ../d/'', because
@code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
doesn't have a clean way to specify an extra final argument for each
invocation of the subject command.  (It can be done by going through a
shell command, but that requires more human labor and brain power than
it should.)

The @option{--target-directory} (@option{-t}) option allows the @command{cp},
@command{install}, @command{ln}, and @command{mv} programs to be used
conveniently with @command{xargs}.  For example, you can move the files
from the current directory to a sibling directory, @code{d} like this:

@smallexample
ls | xargs mv -t ../d --
@end smallexample

However, this doesn't move files whose names begin with @samp{.}.
If you use the GNU @command{find} program, you can move those
files too, with this command:

@example
find . -mindepth 1 -maxdepth 1 \
  | xargs mv -t ../d
@end example

But both of the above approaches fail if there are no files in the
current directory, or if any file has a name containing a blank or
some other special characters.
The following example removes those limitations and requires both
GNU @command{find} and GNU @command{xargs}:

@example
find . -mindepth 1 -maxdepth 1 -print0 \
  | xargs --null --no-run-if-empty \
      mv -t ../d
@end example

@end table

@noindent
The @option{--target-directory} (@option{-t}) and
@option{--no-target-directory} (@option{-T})
options cannot be combined.

@node Trailing slashes
@section Trailing slashes

@cindex trailing slashes

Some GNU programs (at least @command{cp} and @command{mv}) allow you to
remove any trailing slashes from each @var{source} argument before
operating on it.  The @option{--strip-trailing-slashes} option enables
this behavior.

This is useful when a @var{source} argument may have a trailing slash and
@c FIXME: mv's behavior in this case is system-dependent
specify a symbolic link to a directory.  This scenario is in fact rather
common because some shells can automatically append a trailing slash when
performing file name completion on such symbolic links.  Without this
option, @command{mv}, for example, (via the system's rename function) must
interpret a trailing slash as a request to dereference the symbolic link
and so must rename the indirectly referenced @emph{directory} and not
the symbolic link.  Although it may seem surprising that such behavior
be the default, it is required by POSIX and is consistent with
other parts of that standard.

@node Traversing symlinks
@section Traversing symlinks

@cindex symbolic link to directory, controlling traversal of

The following options modify how @command{chown} and @command{chgrp}
@c FIXME: note that 'du' has these options, too, but they have slightly
@c different meaning.
traverse a hierarchy when the @option{--recursive} (@option{-R})
option is also specified.
If more than one of the following options is specified, only the final
one takes effect.
These options specify whether processing a symbolic link to a directory
entails operating on just the symbolic link or on all files in the
hierarchy rooted at that directory.

These options are independent of @option{--dereference} and
@option{--no-dereference} (@option{-h}), which control whether to modify
a symlink or its referent.

@table @samp

@macro choptH
@item -H
@opindex -H
@cindex symbolic link to directory, traverse if on the command line
If @option{--recursive} (@option{-R}) is specified and
a command line argument is a symbolic link to a directory, traverse it.
@end macro
@choptH

@macro choptL
@item -L
@opindex -L
@cindex symbolic link to directory, traverse each that is encountered
In a recursive traversal, traverse every symbolic link to a directory
that is encountered.
@end macro
@choptL

@macro choptP
@item -P
@opindex -P
@cindex symbolic link to directory, never traverse
Do not traverse any symbolic links.
This is the default if none of @option{-H}, @option{-L},
or @option{-P} is specified.
@end macro
@choptP

@end table


@node Treating / specially
@section Treating @file{/} specially

Certain commands can operate destructively on entire hierarchies.
For example, if a user with appropriate privileges mistakenly runs
@samp{rm -rf / tmp/junk}, that may remove
all files on the entire system.  Since there are so few
legitimate uses for such a command,
GNU @command{rm} normally declines to operate on any directory
that resolves to @file{/}.  If you really want to try to remove all
the files on your system, you can use the @option{--no-preserve-root}
option, but the default behavior, specified by the
@option{--preserve-root} option, is safer for most purposes.

The commands @command{chgrp}, @command{chmod} and @command{chown}
can also operate destructively on entire hierarchies, so they too
support these options.  Although, unlike @command{rm}, they don't
actually unlink files, these commands are arguably more dangerous
when operating recursively on @file{/}, since they often work much
more quickly, and hence damage more files before an alert user can
interrupt them.  Tradition and POSIX require these commands
to operate recursively on @file{/}, so they default to
@option{--no-preserve-root}, but using the @option{--preserve-root}
option makes them safer for most purposes.  For convenience you can
specify @option{--preserve-root} in an alias or in a shell function.

Note that the @option{--preserve-root} option also ensures
that @command{chgrp} and @command{chown} do not modify @file{/}
even when dereferencing a symlink pointing to @file{/}.

@node Special built-in utilities
@section Special built-in utilities

Some programs like @command{nice} can invoke other programs; for
example, the command @samp{nice cat file} invokes the program
@command{cat} by executing the command @samp{cat file}.  However,
@dfn{special built-in utilities} like @command{exit} cannot be invoked
this way.  For example, the command @samp{nice exit} does not have a
well-defined behavior: it may generate an error message instead of
exiting.

Here is a list of the special built-in utilities that are standardized
by POSIX 1003.1-2004.

@quotation
@t{.@: : break continue eval exec exit export readonly
return set shift times trap unset}
@end quotation

For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
pwd} do not work as you might expect.

Many shells extend this list.  For example, Bash has several extra
special built-in utilities like @command{history}, and
@command{suspend}, and with Bash the command @samp{nice suspend}
generates an error message instead of suspending.

@node Standards conformance
@section Standards conformance

@vindex POSIXLY_CORRECT
In a few cases, the GNU utilities' default behavior is
incompatible with the POSIX standard.  To suppress these
incompatibilities, define the @env{POSIXLY_CORRECT} environment
variable.  Unless you are checking for POSIX conformance, you
probably do not need to define @env{POSIXLY_CORRECT}.

Newer versions of POSIX are occasionally incompatible with older
versions.  For example, older versions of POSIX required the
command @samp{sort +1} to sort based on the second and succeeding
fields in each input line, but in POSIX 1003.1-2001
the same command is required to sort the file named @file{+1}, and you
must instead use the command @samp{sort -k 2} to get the field-based
sort.  To complicate things further, POSIX 1003.1-2008 allows an
implementation to have either the old or the new behavior.

@vindex _POSIX2_VERSION
The GNU utilities normally conform to the version of POSIX
that is standard for your system.  To cause them to conform to a
different version of POSIX, define the @env{_POSIX2_VERSION}
environment variable to a value of the form @var{yyyymm} specifying
the year and month the standard was adopted.  Three values are currently
supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
POSIX 1003.2-1992, @samp{200112} stands for POSIX
1003.1-2001, and @samp{200809} stands for POSIX 1003.1-2008.
For example, if you have a POSIX 1003.1-2001 system but are running software
containing traditional usage like @samp{sort +1} or @samp{tail +10},
you can work around the compatibility problems by setting
@samp{_POSIX2_VERSION=200809} in your environment.

@c This node is named "Multi-call invocation", not the usual
@c "coreutils invocation", so that shell commands like
@c 'info coreutils "touch invocation"' work as expected.
@node Multi-call invocation
@section @command{coreutils}: Multi-call program

@pindex multicall
@cindex combined
@cindex calling combined multi-call program

The @command{coreutils} command invokes an individual utility, either
implicitly selected by the last component of the name used to invoke
@command{coreutils}, or explicitly with the
@option{--coreutils-prog} option.  Synopsis:

@example
coreutils @option{--coreutils-prog=PROGRAM} @dots{}
@end example

The @command{coreutils} command is not installed by default, so
portable scripts should not rely on its existence.

@node Output of entire files
@chapter Output of entire files

@cindex output of entire files
@cindex entire files, output of

These commands read and write entire files, possibly transforming them
in some way.

@menu
* cat invocation::              Concatenate and write files.
* tac invocation::              Concatenate and write files in reverse.
* nl invocation::               Number lines and write files.
* od invocation::               Write files in octal or other formats.
* base32 invocation::           Transform data into printable data.
* base64 invocation::           Transform data into printable data.
@end menu

@node cat invocation
@section @command{cat}: Concatenate and write files

@pindex cat
@cindex concatenate and write files
@cindex copying files

@command{cat} copies each @var{file} (@samp{-} means standard input), or
standard input if none are given, to standard output.  Synopsis:

@example
cat [@var{option}] [@var{file}]@dots{}
@end example

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -A
@itemx --show-all
@opindex -A
@opindex --show-all
Equivalent to @option{-vET}.

@item -b
@itemx --number-nonblank
@opindex -b
@opindex --number-nonblank
Number all nonempty output lines, starting with 1.

@item -e
@opindex -e
Equivalent to @option{-vE}.

@item -E
@itemx --show-ends
@opindex -E
@opindex --show-ends
Display a @samp{$} after the end of each line.

@item -n
@itemx --number
@opindex -n
@opindex --number
Number all output lines, starting with 1.  This option is ignored
if @option{-b} is in effect.

@item -s
@itemx --squeeze-blank
@opindex -s
@opindex --squeeze-blank
@cindex squeezing empty lines
@cindex squeezing blank lines
Suppress repeated adjacent blank lines; output just one empty line
instead of several.

@item -t
@opindex -t
Equivalent to @option{-vT}.

@item -T
@itemx --show-tabs
@opindex -T
@opindex --show-tabs
Display TAB characters as @samp{^I}.

@item -u
@opindex -u
Ignored; for POSIX compatibility.

@item -v
@itemx --show-nonprinting
@opindex -v
@opindex --show-nonprinting
Display control characters except for LFD and TAB using
@samp{^} notation and precede characters that have the high bit set with
@samp{M-}.

@end table

On systems like MS-DOS that distinguish between text and binary files,
@command{cat} normally reads and writes in binary mode.  However,
@command{cat} reads in text mode if one of the options
@option{-bensAE} is used or if @command{cat} is reading from standard
input and standard input is a terminal.  Similarly, @command{cat}
writes in text mode if one of the options @option{-bensAE} is used or
if standard output is a terminal.

@exitstatus

Examples:

@smallexample
# Output f's contents, then standard input, then g's contents.
cat f - g

# Copy standard input to standard output.
cat
@end smallexample


@node tac invocation
@section @command{tac}: Concatenate and write files in reverse

@pindex tac
@cindex reversing files

@command{tac} copies each @var{file} (@samp{-} means standard input), or
standard input if none are given, to standard output, reversing the
records (lines by default) in each separately.  Synopsis:

@example
tac [@var{option}]@dots{} [@var{file}]@dots{}
@end example

@dfn{Records} are separated by instances of a string (newline by
default).  By default, this separator string is attached to the end of
the record that it follows in the file.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -b
@itemx --before
@opindex -b
@opindex --before
The separator is attached to the beginning of the record that it
precedes in the file.

@item -r
@itemx --regex
@opindex -r
@opindex --regex
Treat the separator string as a regular expression.

@item -s @var{separator}
@itemx --separator=@var{separator}
@opindex -s
@opindex --separator
Use @var{separator} as the record separator, instead of newline.
Note an empty @var{separator} is treated as a zero byte.
I.e., input and output items are delimited with ASCII NUL.

@end table

On systems like MS-DOS that distinguish between text and binary files,
@command{tac} reads and writes in binary mode.

@exitstatus

Example:

@example
# Reverse a file character by character.
tac -r -s 'x\|[^x]'
@end example


@node nl invocation
@section @command{nl}: Number lines and write files

@pindex nl
@cindex numbering lines
@cindex line numbering

@command{nl} writes each @var{file} (@samp{-} means standard input), or
standard input if none are given, to standard output, with line numbers
added to some or all of the lines.  Synopsis:

@example
nl [@var{option}]@dots{} [@var{file}]@dots{}
@end example

@cindex logical pages, numbering on
@command{nl} decomposes its input into (logical) page sections;
by default, the line number is reset to 1 at each logical page section.
@command{nl} treats all of the input files as a single document;
it does not reset line numbers or logical pages between files.

@cindex headers, numbering
@cindex body, numbering
@cindex footers, numbering
A logical page consists of three sections: header, body, and footer.
Any of the sections can be empty.  Each can be numbered in a different
style from the others.

The beginnings of the sections of logical pages are indicated in the
input file by a line containing exactly one of these delimiter strings:

@table @samp
@item \:\:\:
start of header;
@item \:\:
start of body;
@item \:
start of footer.
@end table

The two characters from which these strings are made can be changed from
@samp{\} and @samp{:} via options (see below), but the pattern and
length of each string cannot be changed.

A section delimiter is replaced by an empty line on output.  Any text
that comes before the first section delimiter string in the input file
is considered to be part of a body section, so @command{nl} treats a
file that contains no section delimiters as a single body section.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -b @var{style}
@itemx --body-numbering=@var{style}
@opindex -b
@opindex --body-numbering
Select the numbering style for lines in the body section of each
logical page.  When a line is not numbered, the current line number
is not incremented, but the line number separator character is still
prepended to the line.  The styles are:

@table @samp
@item a
number all lines,
@item t
number only nonempty lines (default for body),
@item n
do not number lines (default for header and footer),
@item p@var{bre}
number only lines that contain a match for the basic regular
expression @var{bre}.
@xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
@end table

@item -d @var{cd}
@itemx --section-delimiter=@var{cd}
@opindex -d
@opindex --section-delimiter
@cindex section delimiters of pages
Set the section delimiter characters to @var{cd}; default is
@samp{\:}.  If only @var{c} is given, the second remains @samp{:}.
(Remember to protect @samp{\} or other metacharacters from shell
expansion with quotes or extra backslashes.)

@item -f @var{style}
@itemx --footer-numbering=@var{style}
@opindex -f
@opindex --footer-numbering
Analogous to @option{--body-numbering}.

@item -h @var{style}
@itemx --header-numbering=@var{style}
@opindex -h
@opindex --header-numbering
Analogous to @option{--body-numbering}.

@item -i @var{number}
@itemx --line-increment=@var{number}
@opindex -i
@opindex --line-increment
Increment line numbers by @var{number} (default 1).

@item -l @var{number}
@itemx --join-blank-lines=@var{number}
@opindex -l
@opindex --join-blank-lines
@cindex empty lines, numbering
@cindex blank lines, numbering
Consider @var{number} (default 1) consecutive empty lines to be one
logical line for numbering, and only number the last one.  Where fewer
than @var{number} consecutive empty lines occur, do not number them.
An empty line is one that contains no characters, not even spaces
or tabs.

@item -n @var{format}
@itemx --number-format=@var{format}
@opindex -n
@opindex --number-format
Select the line numbering format (default is @code{rn}):

@table @samp
@item ln
@opindex ln @r{format for @command{nl}}
left justified, no leading zeros;
@item rn
@opindex rn @r{format for @command{nl}}
right justified, no leading zeros;
@item rz
@opindex rz @r{format for @command{nl}}
right justified, leading zeros.
@end table

@item -p
@itemx --no-renumber
@opindex -p
@opindex --no-renumber
Do not reset the line number at the start of a logical page.

@item -s @var{string}
@itemx --number-separator=@var{string}
@opindex -s
@opindex --number-separator
Separate the line number from the text line in the output with
@var{string} (default is the TAB character).

@item -v @var{number}
@itemx --starting-line-number=@var{number}
@opindex -v
@opindex --starting-line-number
Set the initial line number on each logical page to @var{number} (default 1).

@item -w @var{number}
@itemx --number-width=@var{number}
@opindex -w
@opindex --number-width
Use @var{number} characters for line numbers (default 6).

@end table

@exitstatus


@node od invocation
@section @command{od}: Write files in octal or other formats

@pindex od
@cindex octal dump of files
@cindex hex dump of files
@cindex ASCII dump of files
@cindex file contents, dumping unambiguously

@command{od} writes an unambiguous representation of each @var{file}
(@samp{-} means standard input), or standard input if none are given.
Synopses:

@smallexample
od [@var{option}]@dots{} [@var{file}]@dots{}
od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
od [@var{option}]@dots{} --traditional [@var{file}]@c
 [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
@end smallexample

Each line of output consists of the offset in the input, followed by
groups of data from the file.  By default, @command{od} prints the offset in
octal, and each group of file data is a C @code{short int}'s worth of input
printed as a single octal number.

If @var{offset} is given, it specifies how many input bytes to skip
before formatting and writing.  By default, it is interpreted as an
octal number, but the optional trailing decimal point causes it to be
interpreted as decimal.  If no decimal is specified and the offset
begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
number.  If there is a trailing @samp{b}, the number of bytes skipped
will be @var{offset} multiplied by 512.

If a command is of both the first and second forms, the second form is
assumed if the last operand begins with @samp{+} or (if there are two
operands) a digit.  For example, in @samp{od foo 10} and @samp{od +10}
the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
file name.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -A @var{radix}
@itemx --address-radix=@var{radix}
@opindex -A
@opindex --address-radix
@cindex radix for file offsets
@cindex file offset radix
Select the base in which file offsets are printed.  @var{radix} can
be one of the following:

@table @samp
@item d
decimal;
@item o
octal;
@item x
hexadecimal;
@item n
none (do not print offsets).
@end table

The default is octal.

@item --endian=@var{order}
@opindex --endian
@cindex byte-swapping
@cindex endianness
Reorder input bytes, to handle inputs with differing byte orders,
or to provide consistent output independent of the endian convention
of the current system.  Swapping is performed according to the
specified @option{--type} size and endian @var{order}, which can be
@samp{little} or @samp{big}.

@item -j @var{bytes}
@itemx --skip-bytes=@var{bytes}
@opindex -j
@opindex --skip-bytes
Skip @var{bytes} input bytes before formatting and writing.  If
@var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
in decimal.
@multiplierSuffixes{bytes}

@item -N @var{bytes}
@itemx --read-bytes=@var{bytes}
@opindex -N
@opindex --read-bytes
Output at most @var{bytes} bytes of the input.  Prefixes and suffixes on
@code{bytes} are interpreted as for the @option{-j} option.

@item -S @var{bytes}
@itemx --strings[=@var{bytes}]
@opindex -S
@opindex --strings
@cindex string constants, outputting
Instead of the normal output, output only @dfn{string constants}: at
least @var{bytes} consecutive ASCII graphic characters,
followed by a zero byte (ASCII NUL).
Prefixes and suffixes on @var{bytes} are interpreted as for the
@option{-j} option.

If @var{bytes} is omitted with @option{--strings}, the default is 3.

@item -t @var{type}
@itemx --format=@var{type}
@opindex -t
@opindex --format
Select the format in which to output the file data.  @var{type} is a
string of one or more of the below type indicator characters.  If you
include more than one type indicator character in a single @var{type}
string, or use this option more than once, @command{od} writes one copy
of each output line using each of the data types that you specified,
in the order that you specified.

Adding a trailing ``z'' to any type specification appends a display
of the single byte character representation of the printable characters
to the output line generated by the type specification.

@table @samp
@item a
named character, ignoring high-order bit
@item c
printable single byte character, C backslash escape
or a 3 digit octal sequence
@item d
signed decimal
@item f
floating point (@pxref{Floating point})
@item o
octal
@item u
unsigned decimal
@item x
hexadecimal
@end table

The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
newline, and @samp{nul} for a zero byte.  Only the least significant
seven bits of each byte is used; the high-order bit is ignored.
Type @code{c} outputs
@samp{ }, @samp{\n}, and @code{\0}, respectively.

@cindex type size
Except for types @samp{a} and @samp{c}, you can specify the number
of bytes to use in interpreting each number in the given data type
by following the type indicator character with a decimal integer.
Alternately, you can specify the size of one of the C compiler's
built-in data types by following the type indicator character with
one of the following characters.  For integers (@samp{d}, @samp{o},
@samp{u}, @samp{x}):

@table @samp
@item C
char
@item S
short
@item I
int
@item L
long
@end table

For floating point (@code{f}):

@table @asis
@item F
float
@item D
double
@item L
long double
@end table

@item -v
@itemx --output-duplicates
@opindex -v
@opindex --output-duplicates
Output consecutive lines that are identical.  By default, when two or
more consecutive output lines would be identical, @command{od} outputs only
the first line, and puts just an asterisk on the following line to
indicate the elision.

@item -w[@var{n}]
@itemx --width[=@var{n}]
@opindex -w
@opindex --width
Dump @code{n} input bytes per output line.  This must be a multiple of
the least common multiple of the sizes associated with the specified
output types.

If this option is not given at all, the default is 16.  If @var{n} is
omitted, the default is 32.

@end table

The next several options are shorthands for format specifications.
GNU @command{od} accepts any combination of shorthands and format
specification options.  These options accumulate.

@table @samp

@item -a
@opindex -a
Output as named characters.  Equivalent to @samp{-t a}.

@item -b
@opindex -b
Output as octal bytes.  Equivalent to @samp{-t o1}.

@item -c
@opindex -c
Output as printable single byte characters, C backslash escapes
or 3 digit octal sequences.  Equivalent to @samp{-t c}.

@item -d
@opindex -d
Output as unsigned decimal two-byte units.  Equivalent to @samp{-t u2}.

@item -f
@opindex -f
Output as floats.  Equivalent to @samp{-t fF}.

@item -i
@opindex -i
Output as decimal ints.  Equivalent to @samp{-t dI}.

@item -l
@opindex -l
Output as decimal long ints.  Equivalent to @samp{-t dL}.

@item -o
@opindex -o
Output as octal two-byte units.  Equivalent to @option{-t o2}.

@item -s
@opindex -s
Output as decimal two-byte units.  Equivalent to @option{-t d2}.

@item -x
@opindex -x
Output as hexadecimal two-byte units.  Equivalent to @samp{-t x2}.

@item --traditional
@opindex --traditional
Recognize the non-option label argument that traditional @command{od}
accepted.  The following syntax:

@smallexample
od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
@end smallexample

@noindent
can be used to specify at most one file and optional arguments
specifying an offset and a pseudo-start address, @var{label}.
The @var{label} argument is interpreted
just like @var{offset}, but it specifies an initial pseudo-address.  The
pseudo-addresses are displayed in parentheses following any normal
address.

@end table

@exitstatus


@node base32 invocation
@section @command{base32}: Transform data into printable data

@pindex base32
@cindex base32 encoding

@command{base32} transforms data read from a file, or standard input,
into (or from) base32 encoded form.  The base32 encoded form uses
printable ASCII characters to represent binary data.
The usage and options of this command are precisely the
same as for @command{base64}.  @xref{base64 invocation}.


@node base64 invocation
@section @command{base64}: Transform data into printable data

@pindex base64
@cindex base64 encoding

@command{base64} transforms data read from a file, or standard input,
into (or from) base64 encoded form.  The base64 encoded form uses
printable ASCII characters to represent binary data.
Synopses:

@smallexample
base64 [@var{option}]@dots{} [@var{file}]
base64 --decode [@var{option}]@dots{} [@var{file}]
@end smallexample

The base64 encoding expands data to roughly 133% of the original.
The base32 encoding expands data to roughly 160% of the original.
The format conforms to
@uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -w @var{cols}
@itemx --wrap=@var{cols}
@opindex -w
@opindex --wrap
@cindex wrap data
@cindex column to wrap data after
During encoding, wrap lines after @var{cols} characters.  This must be
a positive number.

The default is to wrap after 76 characters.  Use the value 0 to
disable line wrapping altogether.

@item -d
@itemx --decode
@opindex -d
@opindex --decode
@cindex Decode base64 data
@cindex Base64 decoding
Change the mode of operation, from the default of encoding data, to
decoding data.  Input is expected to be base64 encoded data, and the
output will be the original data.

@item -i
@itemx --ignore-garbage
@opindex -i
@opindex --ignore-garbage
@cindex Ignore garbage in base64 stream
When decoding, newlines are always accepted.
During decoding, ignore unrecognized bytes,
to permit distorted data to be decoded.

@end table

@exitstatus


@node Formatting file contents
@chapter Formatting file contents

@cindex formatting file contents

These commands reformat the contents of files.

@menu
* fmt invocation::              Reformat paragraph text.
* pr invocation::               Paginate or columnate files for printing.
* fold invocation::             Wrap input lines to fit in specified width.
@end menu


@node fmt invocation
@section @command{fmt}: Reformat paragraph text

@pindex fmt
@cindex reformatting paragraph text
@cindex paragraphs, reformatting
@cindex text, reformatting

@command{fmt} fills and joins lines to produce output lines of (at most)
a given number of characters (75 by default).  Synopsis:

@example
fmt [@var{option}]@dots{} [@var{file}]@dots{}
@end example

@command{fmt} reads from the specified @var{file} arguments (or standard
input if none are given), and writes to standard output.

By default, blank lines, spaces between words, and indentation are
preserved in the output; successive input lines with different
indentation are not joined; tabs are expanded on input and introduced on
output.

@cindex line-breaking
@cindex sentences and line-breaking
@cindex Knuth, Donald E.
@cindex Plass, Michael F.
@command{fmt} prefers breaking lines at the end of a sentence, and tries to
avoid line breaks after the first word of a sentence or before the last
word of a sentence.  A @dfn{sentence break} is defined as either the end
of a paragraph or a word ending in any of @samp{.?!}, followed by two
spaces or end of line, ignoring any intervening parentheses or quotes.
Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
breaks; the algorithm is a variant of that given by Donald E. Knuth
and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
@cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
1119--1184.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -c
@itemx --crown-margin
@opindex -c
@opindex --crown-margin
@cindex crown margin
@dfn{Crown margin} mode: preserve the indentation of the first two
lines within a paragraph, and align the left margin of each subsequent
line with that of the second line.

@item -t
@itemx --tagged-paragraph
@opindex -t
@opindex --tagged-paragraph
@cindex tagged paragraphs
@dfn{Tagged paragraph} mode: like crown margin mode, except that if
indentation of the first line of a paragraph is the same as the
indentation of the second, the first line is treated as a one-line
paragraph.

@item -s
@itemx --split-only
@opindex -s
@opindex --split-only
Split lines only.  Do not join short lines to form longer ones.  This
prevents sample lines of code, and other such ``formatted'' text from
being unduly combined.

@item -u
@itemx --uniform-spacing
@opindex -u
@opindex --uniform-spacing
Uniform spacing.  Reduce spacing between words to one space, and spacing
between sentences to two spaces.

@item -@var{width}
@itemx -w @var{width}
@itemx --width=@var{width}
@opindex -@var{width}
@opindex -w
@opindex --width
Fill output lines up to @var{width} characters (default 75 or @var{goal}
plus 10, if @var{goal} is provided).

@item -g @var{goal}
@itemx --goal=@var{goal}
@opindex -g
@opindex --goal
@command{fmt} initially tries to make lines @var{goal} characters wide.
By default, this is 7% shorter than @var{width}.

@item -p @var{prefix}
@itemx --prefix=@var{prefix}
Only lines beginning with @var{prefix} (possibly preceded by whitespace)
are subject to formatting.  The prefix and any preceding whitespace are
stripped for the formatting and then re-attached to each formatted output
line.  One use is to format certain kinds of program comments, while
leaving the code unchanged.

@end table

@exitstatus

@node pr invocation
@section @command{pr}: Paginate or columnate files for printing

@pindex pr
@cindex printing, preparing files for
@cindex multicolumn output, generating
@cindex merging files in parallel

@command{pr} writes each @var{file} (@samp{-} means standard input), or
standard input if none are given, to standard output, paginating and
optionally outputting in multicolumn format; optionally merges all
@var{file}s, printing all in parallel, one per column.  Synopsis:

@example
pr [@var{option}]@dots{} [@var{file}]@dots{}
@end example

@vindex LC_MESSAGES
By default, a 5-line header is printed at each page: two blank lines;
a line with the date, the file name, and the page count; and two more
blank lines.  A footer of five blank lines is also printed.
The default @var{page_length} is 66
lines.  The default number of text lines is therefore 56.
The text line of the header takes the form
@samp{@var{date} @var{string} @var{page}}, with spaces inserted around
@var{string} so that the line takes up the full @var{page_width}.  Here,
@var{date} is the date (see the @option{-D} or @option{--date-format}
option for details), @var{string} is the centered header string, and
@var{page} identifies the page number.  The @env{LC_MESSAGES} locale
category affects the spelling of @var{page}; in the default C locale, it
is @samp{Page @var{number}} where @var{number} is the decimal page
number.

Form feeds in the input cause page breaks in the output.  Multiple form
feeds produce empty pages.

Columns are of equal width, separated by an optional string (default
is @samp{space}).  For multicolumn output, lines will always be truncated to
@var{page_width} (default 72), unless you use the @option{-J} option.
For single
column output no line truncation occurs by default.  Use @option{-W} option to
truncate lines in that case.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item +@var{first_page}[:@var{last_page}]
@itemx --pages=@var{first_page}[:@var{last_page}]
@c The two following @opindex lines evoke warnings because they contain ':'
@c The 'info' spec does not permit that.  If we use those lines, we end
@c up with truncated index entries that don't work.
@c @opindex +@var{first_page}[:@var{last_page}]
@c @opindex --pages=@var{first_page}[:@var{last_page}]
@opindex +@var{page_range}
@opindex --pages=@var{page_range}
Begin printing with page @var{first_page} and stop with @var{last_page}.
Missing @samp{:@var{last_page}} implies end of file.  While estimating
the number of skipped pages each form feed in the input file results
in a new page.  Page counting with and without @samp{+@var{first_page}}
is identical.  By default, counting starts with the first page of input
file (not first page printed).  Line numbering may be altered by @option{-N}
option.

@item -@var{column}
@itemx --columns=@var{column}
@opindex -@var{column}
@opindex --columns
@cindex down columns
With each single @var{file}, produce @var{column} columns of output
(default is 1) and print columns down, unless @option{-a} is used.  The
column width is automatically decreased as @var{column} increases; unless
you use the @option{-W/-w} option to increase @var{page_width} as well.
This option might well cause some lines to be truncated.  The number of
lines in the columns on each page are balanced.  The options @option{-e}
and @option{-i} are on for multiple text-column output.  Together with
@option{-J} option column alignment and line truncation is turned off.
Lines of full length are joined in a free field format and @option{-S}
option may set field separators.  @option{-@var{column}} may not be used
with @option{-m} option.

@item -a
@itemx --across
@opindex -a
@opindex --across
@cindex across columns
With each single @var{file}, print columns across rather than down.  The
@option{-@var{column}} option must be given with @var{column} greater than one.
If a line is too long to fit in a column, it is truncated.

@item -c
@itemx --show-control-chars
@opindex -c
@opindex --show-control-chars
Print control characters using hat notation (e.g., @samp{^G}); print
other nonprinting characters in octal backslash notation.  By default,
nonprinting characters are not changed.

@item -d
@itemx --double-space
@opindex -d
@opindex --double-space
@cindex double spacing
Double space the output.

@item -D @var{format}
@itemx --date-format=@var{format}
@cindex time formats
@cindex formatting times
Format header dates using @var{format}, using the same conventions as
for the command @samp{date +@var{format}}.  @xref{date invocation}.
Except for directives, which start with
@samp{%}, characters in @var{format} are printed unchanged.  You can use
this option to specify an arbitrary string in place of the header date,
e.g., @option{--date-format="Monday morning"}.

@vindex POSIXLY_CORRECT
@vindex LC_TIME
The default date format is @samp{%Y-%m-%d %H:%M} (for example,
@samp{2001-12-04 23:59});
but if the @env{POSIXLY_CORRECT} environment variable is set
and the @env{LC_TIME} locale category specifies the POSIX
locale, the default is @samp{%b %e %H:%M %Y} (for example,
@samp{Dec@ @ 4 23:59 2001}.

@vindex TZ
Time stamps are listed according to the time zone rules specified by
the @env{TZ} environment variable, or by the system default rules if
@env{TZ} is not set.  @xref{TZ Variable,, Specifying the Time Zone
with @env{TZ}, libc, The GNU C Library Reference Manual}.

@item -e[@var{in-tabchar}[@var{in-tabwidth}]]
@itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
@opindex -e
@opindex --expand-tabs
@cindex input tabs
Expand @var{tab}s to spaces on input.  Optional argument @var{in-tabchar} is
the input tab character (default is the TAB character).  Second optional
argument @var{in-tabwidth} is the input tab character's width (default
is 8).

@item -f
@itemx -F
@itemx --form-feed
@opindex -F
@opindex -f
@opindex --form-feed
Use a form feed instead of newlines to separate output pages.  This does
not alter the default page length of 66 lines.

@item -h @var{header}
@itemx --header=@var{header}
@opindex -h
@opindex --header
Replace the file name in the header with the centered string @var{header}.
When using the shell, @var{header} should be quoted and should be
separated from @option{-h} by a space.

@item -i[@var{out-tabchar}[@var{out-tabwidth}]]
@itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
@opindex -i
@opindex --output-tabs
@cindex output tabs
Replace spaces with @var{tab}s on output.  Optional argument @var{out-tabchar}
is the output tab character (default is the TAB character).  Second optional
argument @var{out-tabwidth} is the output tab character's width (default
is 8).

@item -J
@itemx --join-lines
@opindex -J
@opindex --join-lines
Merge lines of full length.  Used together with the column options
@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}.  Turns off
@option{-W/-w} line truncation;
no column alignment used; may be used with
@option{--sep-string[=@var{string}]}.  @option{-J} has been introduced
(together with @option{-W} and @option{--sep-string})
to disentangle the old (POSIX-compliant) options @option{-w} and
@option{-s} along with the three column options.


@item -l @var{page_length}
@itemx --length=@var{page_length}
@opindex -l
@opindex --length
Set the page length to @var{page_length} (default 66) lines, including
the lines of the header [and the footer].  If @var{page_length} is less
than or equal to 10, the header and footer are omitted, as if the
@option{-t} option had been given.

@item -m
@itemx --merge
@opindex -m
@opindex --merge
Merge and print all @var{file}s in parallel, one in each column.  If a
line is too long to fit in a column, it is truncated, unless the @option{-J}
option is used.  @option{--sep-string[=@var{string}]} may be used.
Empty pages in
some @var{file}s (form feeds set) produce empty columns, still marked
by @var{string}.  The result is a continuous line numbering and column
marking throughout the whole merged file.  Completely empty merged pages
show no separators or line numbers.  The default header becomes
@samp{@var{date} @var{page}} with spaces inserted in the middle; this
may be used with the @option{-h} or @option{--header} option to fill up
the middle blank part.

@item -n[@var{number-separator}[@var{digits}]]
@itemx --number-lines[=@var{number-separator}[@var{digits}]]
@opindex -n
@opindex --number-lines
Provide @var{digits} digit line numbering (default for @var{digits} is
5).  With multicolumn output the number occupies the first @var{digits}
column positions of each text column or only each line of @option{-m}
output.  With single column output the number precedes each line just as
@option{-m} does.  Default counting of the line numbers starts with the
first line of the input file (not the first line printed, compare the
@option{--page} option and @option{-N} option).
Optional argument @var{number-separator} is the character appended to
the line number to separate it from the text followed.  The default
separator is the TAB character.  In a strict sense a TAB is always
printed with single column output only.  The TAB width varies
with the TAB position, e.g., with the left @var{margin} specified
by @option{-o} option.  With multicolumn output priority is given to
@samp{equal width of output columns} (a POSIX specification).
The TAB width is fixed to the value of the first column and does
not change with different values of left @var{margin}.  That means a
fixed number of spaces is always printed in the place of the
@var{number-separator} TAB@.  The tabification depends upon the output
position.

@item -N @var{line_number}
@itemx --first-line-number=@var{line_number}
@opindex -N
@opindex --first-line-number
Start line counting with the number @var{line_number} at first line of
first page printed (in most cases not the first line of the input file).

@item -o @var{margin}
@itemx --indent=@var{margin}
@opindex -o
@opindex --indent
@cindex indenting lines
@cindex left margin
Indent each line with a margin @var{margin} spaces wide (default is zero).
The total page width is the size of the margin plus the @var{page_width}
set with the @option{-W/-w} option.  A limited overflow may occur with
numbered single column output (compare @option{-n} option).

@item -r
@itemx --no-file-warnings
@opindex -r
@opindex --no-file-warnings
Do not print a warning message when an argument @var{file} cannot be
opened.  (The exit status will still be nonzero, however.)

@item -s[@var{char}]
@itemx --separator[=@var{char}]
@opindex -s
@opindex --separator
Separate columns by a single character @var{char}.  The default for
@var{char} is the TAB character without @option{-w} and @samp{no
character} with @option{-w}.  Without @option{-s} the default separator
@samp{space} is set.  @option{-s[char]} turns off line truncation of all
three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
@option{-w} is set.  This is a POSIX-compliant formulation.


@item -S[@var{string}]
@itemx --sep-string[=@var{string}]
@opindex -S
@opindex --sep-string
Use @var{string} to separate output columns.  The @option{-S} option doesn't
affect the @option{-W/-w} option, unlike the @option{-s} option which does.  It
does not affect line truncation or column alignment.
Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
separator, TAB@.
Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
(same as @option{-S"@w{ }"}).
If no @samp{@var{string}} argument is specified, @samp{""} is assumed.

@item -t
@itemx --omit-header
@opindex -t
@opindex --omit-header
Do not print the usual header [and footer] on each page, and do not fill
out the bottom of pages (with blank lines or a form feed).  No page
structure is produced, but form feeds set in the input files are retained.
The predefined pagination is not changed.  @option{-t} or @option{-T} may be
useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
in the input file to 4 spaces but don't make any other changes.  Use of
@option{-t} overrides @option{-h}.

@item -T
@itemx --omit-pagination
@opindex -T
@opindex --omit-pagination
Do not print header [and footer].  In addition eliminate all form feeds
set in the input files.

@item -v
@itemx --show-nonprinting
@opindex -v
@opindex --show-nonprinting
Print nonprinting characters in octal backslash notation.

@item -w @var{page_width}
@itemx --width=@var{page_width}
@opindex -w
@opindex --width
Set page width to @var{page_width} characters for multiple text-column
output only (default for @var{page_width} is 72).  The specified
@var{page_width} is rounded down so that columns have equal width.
@option{-s[CHAR]} turns off the default page width and any line truncation
and column alignment.
Lines of full length are merged, regardless of the column options
set.  No @var{page_width} setting is possible with single column output.
A POSIX-compliant formulation.

@item -W @var{page_width}
@itemx --page_width=@var{page_width}
@opindex -W
@opindex --page_width
Set the page width to @var{page_width} characters, honored with and
without a column option.  With a column option, the specified @var{page_width}
is rounded down so that columns have equal width.  Text lines are truncated,
unless @option{-J} is used. Together with one of the three column options
(@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
alignment is always used.  The separator options @option{-S} or @option{-s}
don't disable the @option{-W} option.  Default is 72 characters.  Without
@option{-W @var{page_width}} and without any of the column options NO line
truncation is used (defined to keep downward compatibility and to meet
most frequent tasks).  That's equivalent to @option{-W 72 -J}@.  The header
line is never truncated.

@end table

@exitstatus


@node fold invocation
@section @command{fold}: Wrap input lines to fit in specified width

@pindex fold
@cindex wrapping long input lines
@cindex folding long input lines

@command{fold} writes each @var{file} (@option{-} means standard input), or
standard input if none are given, to standard output, breaking long
lines.  Synopsis:

@example
fold [@var{option}]@dots{} [@var{file}]@dots{}
@end example

By default, @command{fold} breaks lines wider than 80 columns.  The output
is split into as many lines as necessary.

@cindex screen columns
@command{fold} counts screen columns by default; thus, a tab may count more
than one column, backspace decreases the column count, and carriage
return sets the column to zero.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -b
@itemx --bytes
@opindex -b
@opindex --bytes
Count bytes rather than columns, so that tabs, backspaces, and carriage
returns are each counted as taking up one column, just like other
characters.

@item -s
@itemx --spaces
@opindex -s
@opindex --spaces
Break at word boundaries: the line is broken after the last blank before
the maximum line length.  If the line contains no such blanks, the line
is broken at the maximum line length as usual.

@item -w @var{width}
@itemx --width=@var{width}
@opindex -w
@opindex --width
Use a maximum line length of @var{width} columns instead of 80.

For compatibility @command{fold} supports an obsolete option syntax
@option{-@var{width}}.  New scripts should use @option{-w @var{width}}
instead.

@end table

@exitstatus


@node Output of parts of files
@chapter Output of parts of files

@cindex output of parts of files
@cindex parts of files, output of

These commands output pieces of the input.

@menu
* head invocation::             Output the first part of files.
* tail invocation::             Output the last part of files.
* split invocation::            Split a file into pieces.
* csplit invocation::           Split a file into context-determined pieces.
@end menu

@node head invocation
@section @command{head}: Output the first part of files

@pindex head
@cindex initial part of files, outputting
@cindex first part of files, outputting

@command{head} prints the first part (10 lines by default) of each
@var{file}; it reads from standard input if no files are given or
when given a @var{file} of @option{-}.  Synopsis:

@example
head [@var{option}]@dots{} [@var{file}]@dots{}
@end example

If more than one @var{file} is specified, @command{head} prints a
one-line header consisting of:

@example
==> @var{file name} <==
@end example

@noindent
before the output for each @var{file}.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -c [-]@var{num}
@itemx --bytes=[-]@var{num}
@opindex -c
@opindex --bytes
Print the first @var{num} bytes, instead of initial lines.
However, if @var{num} is prefixed with a @samp{-},
print all but the last @var{num} bytes of each file.
@multiplierSuffixes{num}

@item -n [-]@var{num}
@itemx --lines=[-]@var{num}
@opindex -n
@opindex --lines
Output the first @var{num} lines.
However, if @var{num} is prefixed with a @samp{-},
print all but the last @var{num} lines of each file.
Size multiplier suffixes are the same as with the @option{-c} option.

@item -q
@itemx --quiet
@itemx --silent
@opindex -q
@opindex --quiet
@opindex --silent
Never print file name headers.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Always print file name headers.

@optZeroTerminated

@end table

For compatibility @command{head} also supports an obsolete option syntax
@option{-[@var{num}][bkm][cqv]}, which is recognized only if it is
specified first.  @var{num} is a decimal number optionally followed
by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
@samp{l} to mean count by lines, or other option letters (@samp{cqv}).
Scripts intended for standard hosts should use @option{-c @var{num}}
or @option{-n @var{num}} instead.  If your script must also run on
hosts that support only the obsolete syntax, it is usually simpler to
avoid @command{head}, e.g., by using @samp{sed 5q} instead of
@samp{head -5}.

@exitstatus


@node tail invocation
@section @command{tail}: Output the last part of files

@pindex tail
@cindex last part of files, outputting

@command{tail} prints the last part (10 lines by default) of each
@var{file}; it reads from standard input if no files are given or
when given a @var{file} of @samp{-}.  Synopsis:

@example
tail [@var{option}]@dots{} [@var{file}]@dots{}
@end example

If more than one @var{file} is specified, @command{tail} prints a
one-line header before the output for each @var{file}, consisting of:

@example
==> @var{file name} <==
@end example

For further processing of tail output, it can be useful to convert the
file headers to line prefixes, which can be done like:

@example
tail @dots{} |
awk '
  /^==> .* <==$/ @{prefix=substr($0,5,length-8)":"; next@}
  @{print prefix$0@}
' | @dots{}
@end example

@cindex BSD @command{tail}
GNU @command{tail} can output any amount of data (some other versions of
@command{tail} cannot).  It also has no @option{-r} option (print in
reverse), since reversing a file is really a different job from printing
the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
only reverse files that are at most as large as its buffer, which is
typically 32 KiB@.  A more reliable and versatile way to reverse files is
the GNU @command{tac} command.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -c [+]@var{num}
@itemx --bytes=[+]@var{num}
@opindex -c
@opindex --bytes
Output the last @var{num} bytes, instead of final lines.
However, if @var{num} is prefixed with a @samp{+}, start printing with
byte @var{num} from the start of each file, instead of from the end.
@multiplierSuffixes{num}

@item -f
@itemx --follow[=@var{how}]
@opindex -f
@opindex --follow
@cindex growing files
@vindex name @r{follow option}
@vindex descriptor @r{follow option}
Loop forever trying to read more characters at the end of the file,
presumably because the file is growing.
If more than one file is given, @command{tail} prints a header whenever it
gets output from a different file, to indicate which file that output is
from.

There are two ways to specify how you'd like to track files with this option,
but that difference is noticeable only when a followed file is removed or
renamed.
If you'd like to continue to track the end of a growing file even after
it has been unlinked, use @option{--follow=descriptor}.  This is the default
behavior, but it is not useful if you're tracking a log file that may be
rotated (removed or renamed, then reopened).  In that case, use
@option{--follow=name} to track the named file, perhaps by reopening it
periodically to see if it has been removed and recreated by some other program.
Note that the inotify-based implementation handles this case without
the need for any periodic reopening.

No matter which method you use, if the tracked file is determined to have
shrunk, @command{tail} prints a message saying the file has been truncated
and resumes tracking the end of the file from the newly-determined endpoint.

When a file is removed, @command{tail}'s behavior depends on whether it is
following the name or the descriptor.  When following by name, tail can
detect that a file has been removed and gives a message to that effect,
and if @option{--retry} has been specified it will continue checking
periodically to see if the file reappears.
When following a descriptor, tail does not detect that the file has
been unlinked or renamed and issues no message;  even though the file
may no longer be accessible via its original name, it may still be
growing.

The option values @samp{descriptor} and @samp{name} may be specified only
with the long form of the option, not with @option{-f}.

The @option{-f} option is ignored if
no @var{file} operand is specified and standard input is a FIFO or a pipe.
Likewise, the @option{-f} option has no effect for any
operand specified as @samp{-}, when standard input is a FIFO or a pipe.

With kernel inotify support, output is triggered by file changes
and is generally very prompt.
Otherwise, @command{tail} sleeps for one second between checks---
use @option{--sleep-interval=@var{n}} to change that default---which can
make the output appear slightly less responsive or bursty.
When using tail without inotify support, you can make it more responsive
by using a sub-second sleep interval, e.g., via an alias like this:

@example
alias tail='tail -s.1'
@end example

@item -F
@opindex -F
This option is the same as @option{--follow=name --retry}.  That is, tail
will attempt to reopen a file when it is removed.  Should this fail, tail
will keep trying until it becomes accessible again.

@item --max-unchanged-stats=@var{n}
@opindex --max-unchanged-stats
When tailing a file by name, if there have been @var{n} (default
n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
iterations for which the file has not changed, then
@code{open}/@code{fstat} the file to determine if that file name is
still associated with the same device/inode-number pair as before.
When following a log file that is rotated, this is approximately the
number of seconds between when tail prints the last pre-rotation lines
and when it prints the lines that have accumulated in the new log file.
This option is meaningful only when polling (i.e., without inotify)
and when following by name.

@item -n [+]@var{num}
@itemx --lines=[+]@var{}
@opindex -n
@opindex --lines
Output the last @var{num} lines.
However, if @var{num} is prefixed with a @samp{+}, start printing with
line @var{num} from the start of each file, instead of from the end.
Size multiplier suffixes are the same as with the @option{-c} option.

@item --pid=@var{pid}
@opindex --pid
When following by name or by descriptor, you may specify the process ID,
@var{pid}, of the sole writer of all @var{file} arguments.  Then, shortly
after that process terminates, tail will also terminate.  This will
work properly only if the writer and the tailing process are running on
the same machine.  For example, to save the output of a build in a file
and to watch the file grow, if you invoke @command{make} and @command{tail}
like this then the tail process will stop when your build completes.
Without this option, you would have had to kill the @code{tail -f}
process yourself.

@example
$ make >& makerr & tail --pid=$! -f makerr
@end example

If you specify a @var{pid} that is not in use or that does not correspond
to the process that is writing to the tailed files, then @command{tail}
may terminate long before any @var{file}s stop growing or it may not
terminate until long after the real writer has terminated.
Note that @option{--pid} cannot be supported on some systems; @command{tail}
will print a warning if this is the case.

@item -q
@itemx --quiet
@itemx --silent
@opindex -q
@opindex --quiet
@opindex --silent
Never print file name headers.

@item --retry
@opindex --retry
Indefinitely try to open the specified file.
This option is useful mainly when following (and otherwise issues a warning).

When following by file descriptor (i.e., with @option{--follow=descriptor}),
this option only affects the initial open of the file, as after a successful
open, @command{tail} will start following the file descriptor.

When following by name (i.e., with @option{--follow=name}), @command{tail}
infinitely retries to re-open the given files until killed.

Without this option, when @command{tail} encounters a file that doesn't
exist or is otherwise inaccessible, it reports that fact and
never checks it again.

@item -s @var{number}
@itemx --sleep-interval=@var{number}
@opindex -s
@opindex --sleep-interval
Change the number of seconds to wait between iterations (the default is 1.0).
During one iteration, every specified file is checked to see if it has
changed size.
Historical implementations of @command{tail} have required that
@var{number} be an integer.  However, GNU @command{tail} accepts
an arbitrary floating point number.  @xref{Floating point}.
When @command{tail} uses inotify, this polling-related option
is usually ignored.  However, if you also specify @option{--pid=@var{p}},
@command{tail} checks whether process @var{p} is alive at least
every @var{number} seconds.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Always print file name headers.

@optZeroTerminated

@end table

For compatibility @command{tail} also supports an obsolete usage
@samp{tail -[@var{num}][bcl][f] [@var{file}]}, which is recognized
only if it does not conflict with the usage described
above.  This obsolete form uses exactly one option and at most one
file.  In the option, @var{num} is an optional decimal number optionally
followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
which has the same meaning as @option{-f}.

@vindex _POSIX2_VERSION
On systems not conforming to POSIX 1003.1-2001, the leading @samp{-}
can be replaced by @samp{+} in the traditional option syntax with the
same meaning as in counts, and on obsolete systems predating POSIX
1003.1-2001 traditional usage overrides normal usage when the two
conflict.  This behavior can be controlled with the
@env{_POSIX2_VERSION} environment variable (@pxref{Standards
conformance}).

Scripts intended for use on standard hosts should avoid traditional
syntax and should use @option{-c @var{num}[b]}, @option{-n
@var{num}}, and/or @option{-f} instead.  If your script must also
run on hosts that support only the traditional syntax, you can often
rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
'$p'} rather than @samp{tail -1}.  If that's not possible, the script
can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
then @dots{}} to decide which syntax to use.

Even if your script assumes the standard behavior, you should still
beware usages whose behaviors differ depending on the POSIX
version.  For example, avoid @samp{tail - main.c}, since it might be
interpreted as either @samp{tail main.c} or as @samp{tail -- -
main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
-c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
mean either @samp{tail ./+4} or @samp{tail -n +4}.

@exitstatus


@node split invocation
@section @command{split}: Split a file into pieces.

@pindex split
@cindex splitting a file into pieces
@cindex pieces, splitting a file into

@command{split} creates output files containing consecutive or interleaved
sections of @var{input}  (standard input if none is given or @var{input}
is @samp{-}).  Synopsis:

@example
split [@var{option}] [@var{input} [@var{prefix}]]
@end example

By default, @command{split} puts 1000 lines of @var{input} (or whatever is
left over for the last section), into each output file.

@cindex output file name prefix
The output files' names consist of @var{prefix} (@samp{x} by default)
followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
default), such that concatenating the output files in traditional
sorted order by file name produces the original input file (except
@option{-nr/@var{n}}).  By default split will initially create files
with two generated suffix characters, and will increase this width by two
when the next most significant position reaches the last character.
(@samp{yz}, @samp{zaaa}, @samp{zaab}, @dots{}).  In this way an arbitrary
number of output files are supported, which sort as described above,
even in the presence of an @option{--additional-suffix} option.
If the @option{-a} option is specified and the output file names are
exhausted, @command{split} reports an error without deleting the
output files that it did create.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -l @var{lines}
@itemx --lines=@var{lines}
@opindex -l
@opindex --lines
Put @var{lines} lines of @var{input} into each output file.
If @option{--separator} is specified, then @var{lines} determines
the number of records.

For compatibility @command{split} also supports an obsolete
option syntax @option{-@var{lines}}.  New scripts should use
@option{-l @var{lines}} instead.

@item -b @var{size}
@itemx --bytes=@var{size}
@opindex -b
@opindex --bytes
Put @var{size} bytes of @var{input} into each output file.
@multiplierSuffixes{size}

@item -C @var{size}
@itemx --line-bytes=@var{size}
@opindex -C
@opindex --line-bytes
Put into each output file as many complete lines of @var{input} as
possible without exceeding @var{size} bytes.  Individual lines or records
longer than @var{size} bytes are broken into multiple files.
@var{size} has the same format as for the @option{--bytes} option.
If @option{--separator} is specified, then @var{lines} determines
the number of records.

@item --filter=@var{command}
@opindex --filter
With this option, rather than simply writing to each output file,
write through a pipe to the specified shell @var{command} for each output file.
@var{command} should use the $FILE environment variable, which is set
to a different output file name for each invocation of the command.
For example, imagine that you have a 1TiB compressed file
that, if uncompressed, would be too large to reside on disk,
yet you must split it into individually-compressed pieces
of a more manageable size.
To do that, you might run this command:

@example
xz -dc BIG.xz | split -b200G --filter='xz > $FILE.xz' - big-
@end example

Assuming a 10:1 compression ratio, that would create about fifty 20GiB files
with names @file{big-aa.xz}, @file{big-ab.xz}, @file{big-ac.xz}, etc.

@item -n @var{chunks}
@itemx --number=@var{chunks}
@opindex -n
@opindex --number

Split @var{input} to @var{chunks} output files where @var{chunks} may be:

@example
@var{n}      generate @var{n} files based on current size of @var{input}
@var{k}/@var{n}    only output @var{k}th of @var{n} to stdout
l/@var{n}    generate @var{n} files without splitting lines or records
l/@var{k}/@var{n}  likewise but only output @var{k}th of @var{n} to stdout
r/@var{n}    like @samp{l} but use round robin distribution
r/@var{k}/@var{n}  likewise but only output @var{k}th of @var{n} to stdout
@end example

Any excess bytes remaining after dividing the @var{input}
into @var{n} chunks, are assigned to the last chunk.
Any excess bytes appearing after the initial calculation are discarded
(except when using @samp{r} mode).

All @var{n} files are created even if there are fewer than @var{n} lines,
or the @var{input} is truncated.

For @samp{l} mode, chunks are approximately @var{input} size / @var{n}.
The @var{input} is partitioned into @var{n} equal sized portions, with
the last assigned any excess.  If a line @emph{starts} within a partition
it is written completely to the corresponding file.  Since lines or records
are not split even if they overlap a partition, the files written
can be larger or smaller than the partition size, and even empty
if a line/record is so long as to completely overlap the partition.

For @samp{r} mode, the size of @var{input} is irrelevant,
and so can be a pipe for example.

@item -a @var{length}
@itemx --suffix-length=@var{length}
@opindex -a
@opindex --suffix-length
Use suffixes of length @var{length}.  If a @var{length} of 0 is specified,
this is the same as if (any previous) @option{-a} was not specified, and
thus enables the default behavior, which starts the suffix length at 2,
and unless @option{-n} or @option{--numeric-suffixes=@var{from}} is
specified, will auto increase the length by 2 as required.

@item -d
@itemx --numeric-suffixes[=@var{from}]
@opindex -d
@opindex --numeric-suffixes
Use digits in suffixes rather than lower-case letters.  The numerical
suffix counts from @var{from} if specified, 0 otherwise.

@var{from} is supported with the long form option, and is used to either set the
initial suffix for a single run, or to set the suffix offset for independently
split inputs, and consequently the auto suffix length expansion described above
is disabled.  Therefore you may also want to use option @option{-a} to allow
suffixes beyond @samp{99}.  Note if option @option{--number} is specified and
the number of files is less than @var{from}, a single run is assumed and the
minimum suffix length required is automatically determined.

@item --additional-suffix=@var{suffix}
@opindex --additional-suffix
Append an additional @var{suffix} to output file names.  @var{suffix}
must not contain slash.

@item -e
@itemx --elide-empty-files
@opindex -e
@opindex --elide-empty-files
Suppress the generation of zero-length output files.  This can happen
with the @option{--number} option if a file is (truncated to be) shorter
than the number requested, or if a line is so long as to completely
span a chunk.  The output file sequence numbers, always run consecutively
even when this option is specified.

@item -t @var{separator}
@itemx --separator=@var{separator}
@opindex -t
@opindex --separator
@cindex line separator character
@cindex record separator character
Use character @var{separator} as the record separator instead of the default
newline character (ASCII LF).
To specify ASCII NUL as the separator, use the two-character string @samp{\0},
e.g., @samp{split -t '\0'}.

@item -u
@itemx --unbuffered
@opindex -u
@opindex --unbuffered
Immediately copy input to output in @option{--number r/@dots{}} mode,
which is a much slower mode of operation.

@item --verbose
@opindex --verbose
Write a diagnostic just before each output file is opened.

@end table

@exitstatus

Here are a few examples to illustrate how the
@option{--number} (@option{-n}) option works:

Notice how, by default, one line may be split onto two or more:

@example
$ seq -w 6 10 > k; split -n3 k; head xa?
==> xaa <==
06
07
==> xab <==

08
0
==> xac <==
9
10
@end example

Use the "l/" modifier to suppress that:

@example
$ seq -w 6 10 > k; split -nl/3 k; head xa?
==> xaa <==
06
07

==> xab <==
08
09

==> xac <==
10
@end example

Use the "r/" modifier to distribute lines in a round-robin fashion:

@example
$ seq -w 6 10 > k; split -nr/3 k; head xa?
==> xaa <==
06
09

==> xab <==
07
10

==> xac <==
08
@end example

You can also extract just the Kth chunk.
This extracts and prints just the 7th "chunk" of 33:

@example
$ seq 100 > k; split -nl/7/33 k
20
21
22
@end example


@node csplit invocation
@section @command{csplit}: Split a file into context-determined pieces

@pindex csplit
@cindex context splitting
@cindex splitting a file into pieces by context

@command{csplit} creates zero or more output files containing sections of
@var{input} (standard input if @var{input} is @samp{-}).  Synopsis:

@example
csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
@end example

The contents of the output files are determined by the @var{pattern}
arguments, as detailed below.  An error occurs if a @var{pattern}
argument refers to a nonexistent line of the input file (e.g., if no
remaining line matches a given regular expression).  After every
@var{pattern} has been matched, any remaining input is copied into one
last output file.

By default, @command{csplit} prints the number of bytes written to each
output file after it has been created.

The types of pattern arguments are:

@table @samp

@item @var{n}
Create an output file containing the input up to but not including line
@var{n} (a positive integer).  If followed by a repeat count, also
create an output file containing the next @var{n} lines of the input
file once for each repeat.

@item /@var{regexp}/[@var{offset}]
Create an output file containing the current line up to (but not
including) the next line of the input file that contains a match for
@var{regexp}.  The optional @var{offset} is an integer.
If it is given, the input up to (but not including) the
matching line plus or minus @var{offset} is put into the output file,
and the line after that begins the next section of input.

@item %@var{regexp}%[@var{offset}]
Like the previous type, except that it does not create an output
file, so that section of the input file is effectively ignored.

@item @{@var{repeat-count}@}
Repeat the previous pattern @var{repeat-count} additional
times.  The @var{repeat-count} can either be a positive integer or an
asterisk, meaning repeat as many times as necessary until the input is
exhausted.

@end table

The output files' names consist of a prefix (@samp{xx} by default)
followed by a suffix.  By default, the suffix is an ascending sequence
of two-digit decimal numbers from @samp{00} to @samp{99}.  In any case,
concatenating the output files in sorted order by file name produces the
original input file.

By default, if @command{csplit} encounters an error or receives a hangup,
interrupt, quit, or terminate signal, it removes any output files
that it has created so far before it exits.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -f @var{prefix}
@itemx --prefix=@var{prefix}
@opindex -f
@opindex --prefix
@cindex output file name prefix
Use @var{prefix} as the output file name prefix.

@item -b @var{format}
@itemx --suffix-format=@var{format}
@opindex -b
@opindex --suffix-format
@cindex output file name suffix
Use @var{format} as the output file name suffix.  When this option is
specified, the suffix string must include exactly one
@code{printf(3)}-style conversion specification, possibly including
format specification flags, a field width, a precision specifications,
or all of these kinds of modifiers.  The format letter must convert a
binary unsigned integer argument to readable form.  The format letters
@samp{d} and @samp{i} are aliases for @samp{u}, and the
@samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed.  The
entire @var{format} is given (with the current output file number) to
@code{sprintf(3)} to form the file name suffixes for each of the
individual output files in turn.  If this option is used, the
@option{--digits} option is ignored.

@item -n @var{digits}
@itemx --digits=@var{digits}
@opindex -n
@opindex --digits
Use output file names containing numbers that are @var{digits} digits
long instead of the default 2.

@item -k
@itemx --keep-files
@opindex -k
@opindex --keep-files
Do not remove output files when errors are encountered.

@item --suppress-matched
@opindex --suppress-matched
Do not output lines matching the specified @var{pattern}.
I.e., suppress the boundary line from the start of the second
and subsequent splits.

@item -z
@itemx --elide-empty-files
@opindex -z
@opindex --elide-empty-files
Suppress the generation of zero-length output files.  (In cases where
the section delimiters of the input file are supposed to mark the first
lines of each of the sections, the first output file will generally be a
zero-length file unless you use this option.)  The output file sequence
numbers always run consecutively starting from 0, even when this option
is specified.

@item -s
@itemx -q
@itemx --silent
@itemx --quiet
@opindex -s
@opindex -q
@opindex --silent
@opindex --quiet
Do not print counts of output file sizes.

@end table

@exitstatus

Here is an example of its usage.
First, create an empty directory for the exercise,
and cd into it:

@example
$ mkdir d && cd d
@end example

Now, split the sequence of 1..14 on lines that end with 0 or 5:

@example
$ seq 14 | csplit - '/[05]$/' '@{*@}'
8
10
15
@end example

Each number printed above is the size of an output
file that csplit has just created.
List the names of those output files:

@example
$ ls
xx00  xx01  xx02
@end example

Use @command{head} to show their contents:

@example
$ head xx*
==> xx00 <==
1
2
3
4

==> xx01 <==
5
6
7
8
9

==> xx02 <==
10
11
12
13
14
@end example

Example of splitting input by empty lines:

@example
$ csplit --suppress-matched @var{input.txt} '/^$/' '@{*@}'
@end example

@c
@c TODO: "uniq" already supports "--group".
@c        when it gets the "--key" option, uncomment this example.
@c
@c Example of splitting input file, based on the value of column 2:
@c
@c @example
@c $ cat @var{input.txt} |
@c       sort -k2,2 |
@c       uniq --group -k2,2 |
@c       csplit -m '/^$/' '@{*@}'
@c @end example

@node Summarizing files
@chapter Summarizing files

@cindex summarizing files

These commands generate just a few numbers representing entire
contents of files.

@menu
* wc invocation::               Print newline, word, and byte counts.
* sum invocation::              Print checksum and block counts.
* cksum invocation::            Print CRC checksum and byte counts.
* md5sum invocation::           Print or check MD5 digests.
* sha1sum invocation::          Print or check SHA-1 digests.
* sha2 utilities::              Print or check SHA-2 digests.
@end menu


@node wc invocation
@section @command{wc}: Print newline, word, and byte counts

@pindex wc
@cindex byte count
@cindex character count
@cindex word count
@cindex line count

@command{wc} counts the number of bytes, characters, whitespace-separated
words, and newlines in each given @var{file}, or standard input if none
are given or for a @var{file} of @samp{-}.  Synopsis:

@example
wc [@var{option}]@dots{} [@var{file}]@dots{}
@end example

@cindex total counts
@command{wc} prints one line of counts for each file, and if the file was
given as an argument, it prints the file name following the counts.  If
more than one @var{file} is given, @command{wc} prints a final line
containing the cumulative counts, with the file name @file{total}.  The
counts are printed in this order: newlines, words, characters, bytes,
maximum line length.
Each count is printed right-justified in a field with at least one
space between fields so that the numbers and file names normally line
up nicely in columns.  The width of the count fields varies depending
on the inputs, so you should not depend on a particular field width.
However, as a GNU extension, if only one count is printed,
it is guaranteed to be printed without leading spaces.

By default, @command{wc} prints three counts: the newline, words, and byte
counts.  Options can specify that only certain counts be printed.
Options do not undo others previously given, so

@example
wc --bytes --words
@end example

@noindent
prints both the byte counts and the word counts.

With the @option{--max-line-length} option, @command{wc} prints the length
of the longest line per file, and if there is more than one file it
prints the maximum (not the sum) of those lengths.  The line lengths here
are measured in screen columns, according to the current locale and
assuming tab positions in every 8th column.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -c
@itemx --bytes
@opindex -c
@opindex --bytes
Print only the byte counts.

@item -m
@itemx --chars
@opindex -m
@opindex --chars
Print only the character counts.

@item -w
@itemx --words
@opindex -w
@opindex --words
Print only the word counts.

@item -l
@itemx --lines
@opindex -l
@opindex --lines
Print only the newline counts.

@item -L
@itemx --max-line-length
@opindex -L
@opindex --max-line-length
Print only the maximum display widths.
Tabs are set at every 8th column.
Display widths of wide characters are considered.
Non-printable characters are given 0 width.

@macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
@item --files0-from=@var{file}
@opindex --files0-from=@var{file}
@c This is commented out to avoid a texi2dvi failure.
@c texi2dvi (GNU Texinfo 4.11) 1.104
@c @cindex including files from @command{\cmd\}
Disallow processing files named on the command line, and instead process
those named in file @var{file}; each name being terminated by a zero byte
(ASCII NUL).
This is useful \withTotalOption\
when the list of file names is so long that it may exceed a command line
length limitation.
In such cases, running @command{\cmd\} via @command{xargs} is undesirable
because it splits the list into pieces and makes @command{\cmd\} print
\subListOutput\ for each sublist rather than for the entire list.
One way to produce a list of ASCII NUL terminated file
names is with GNU
@command{find}, using its @option{-print0} predicate.
If @var{file} is @samp{-} then the ASCII NUL terminated
file names are read from standard input.
@end macro
@filesZeroFromOption{wc,,a total}

For example, to find the length of the longest line in any @file{.c} or
@file{.h} file in the current hierarchy, do this:

@example
find . -name '*.[ch]' -print0 |
  wc -L --files0-from=- | tail -n1
@end example

@end table

@exitstatus


@node sum invocation
@section @command{sum}: Print checksum and block counts

@pindex sum
@cindex 16-bit checksum
@cindex checksum, 16-bit

@command{sum} computes a 16-bit checksum for each given @var{file}, or
standard input if none are given or for a @var{file} of @samp{-}.  Synopsis:

@example
sum [@var{option}]@dots{} [@var{file}]@dots{}
@end example

@command{sum} prints the checksum for each @var{file} followed by the
number of blocks in the file (rounded up).  If more than one @var{file}
is given, file names are also printed (by default).  (With the
@option{--sysv} option, corresponding file names are printed when there is
at least one file argument.)

By default, GNU @command{sum} computes checksums using an algorithm
compatible with BSD @command{sum} and prints file sizes in units of
1024-byte blocks.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -r
@opindex -r
@cindex BSD @command{sum}
Use the default (BSD compatible) algorithm.  This option is included for
compatibility with the System V @command{sum}.  Unless @option{-s} was also
given, it has no effect.

@item -s
@itemx --sysv
@opindex -s
@opindex --sysv
@cindex System V @command{sum}
Compute checksums using an algorithm compatible with System V
@command{sum}'s default, and print file sizes in units of 512-byte blocks.

@end table

@command{sum} is provided for compatibility; the @command{cksum} program (see
next section) is preferable in new applications.

@exitstatus


@node cksum invocation
@section @command{cksum}: Print CRC checksum and byte counts

@pindex cksum
@cindex cyclic redundancy check
@cindex CRC checksum

@command{cksum} computes a cyclic redundancy check (CRC) checksum for each
given @var{file}, or standard input if none are given or for a
@var{file} of @samp{-}.  Synopsis:

@example
cksum [@var{option}]@dots{} [@var{file}]@dots{}
@end example

@command{cksum} prints the CRC checksum for each file along with the number
of bytes in the file, and the file name unless no arguments were given.

@command{cksum} is typically used to ensure that files
transferred by unreliable means (e.g., netnews) have not been corrupted,
by comparing the @command{cksum} output for the received files with the
@command{cksum} output for the original files (typically given in the
distribution).

The CRC algorithm is specified by the POSIX standard.  It is not
compatible with the BSD or System V @command{sum} algorithms (see the
previous section); it is more robust.

The only options are @option{--help} and @option{--version}.  @xref{Common
options}.

@exitstatus


@node md5sum invocation
@section @command{md5sum}: Print or check MD5 digests

@pindex md5sum
@cindex MD5
@cindex 128-bit checksum
@cindex checksum, 128-bit
@cindex fingerprint, 128-bit
@cindex message-digest, 128-bit

@command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
@dfn{message-digest}) for each specified @var{file}.

Note: The MD5 digest is more reliable than a simple CRC (provided by
the @command{cksum} command) for detecting accidental file corruption,
as the chances of accidentally having two files with identical MD5
are vanishingly small.  However, it should not be considered secure
against malicious tampering: although finding a file with a given MD5
fingerprint is considered infeasible at the moment, it is known how
to modify certain files, including digital certificates, so that they
appear valid when signed with an MD5 digest.
For more secure hashes, consider using SHA-2.  @xref{sha2 utilities}.

If a @var{file} is specified as @samp{-} or if no files are given
@command{md5sum} computes the checksum for the standard input.
@command{md5sum} can also determine whether a file and checksum are
consistent.  Synopsis:

@example
md5sum [@var{option}]@dots{} [@var{file}]@dots{}
@end example

For each @var{file}, @samp{md5sum} outputs by default, the MD5 checksum,
a space, a flag indicating binary or text input mode, and the file name.
Binary mode is indicated with @samp{*}, text mode with @samp{ } (space).
Binary mode is the default on systems where it's significant,
otherwise text mode is the default.
If @var{file} contains a backslash or newline, the
line is started with a backslash, and each problematic character in
the file name is escaped with a backslash, making the output
unambiguous even in the presence of arbitrary file names.
If @var{file} is omitted or specified as @samp{-}, standard input is read.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -b
@itemx --binary
@opindex -b
@opindex --binary
@cindex binary input files
Treat each input file as binary, by reading it in binary mode and
outputting a @samp{*} flag.  This is the inverse of @option{--text}.
On systems like GNU that do not distinguish between binary
and text files, this option merely flags each input mode as binary:
the MD5 checksum is unaffected.  This option is the default on systems
like MS-DOS that distinguish between binary and text files, except
for reading standard input when standard input is a terminal.

@item -c
@itemx --check
Read file names and checksum information (not data) from each
@var{file} (or from stdin if no @var{file} was specified) and report
whether the checksums match the contents of the named files.
The input to this mode of @command{md5sum} is usually the output of
a prior, checksum-generating run of @samp{md5sum}.
Three input formats are supported.  Either the default output
format described above, the @option{--tag} output format,
or the BSD reversed mode format which is similar to the default mode,
but doesn't use a character to distinguish binary and text modes.
@sp 1
For each such line, @command{md5sum} reads the named file and computes its
MD5 checksum.  Then, if the computed message digest does not match the
one on the line with the file name, the file is noted as having
failed the test.  Otherwise, the file passes the test.
By default, for each valid line, one line is written to standard
output indicating whether the named file passed the test.
After all checks have been performed, if there were any failures,
a warning is issued to standard error.
Use the @option{--status} option to inhibit that output.
If any listed file cannot be opened or read, if any valid line has
an MD5 checksum inconsistent with the associated file, or if no valid
line is found, @command{md5sum} exits with nonzero status.  Otherwise,
it exits successfully.

@item --ignore-missing
@opindex --ignore-missing
@cindex verifying MD5 checksums
This option is useful only when verifying checksums.
When verifying checksums, don't fail or report any status
for missing files.  This is useful when verifying a subset
of downloaded files given a larger list of checksums.

@item --quiet
@opindex --quiet
@cindex verifying MD5 checksums
This option is useful only when verifying checksums.
When verifying checksums, don't generate an 'OK' message per successfully
checked file.  Files that fail the verification are reported in the
default one-line-per-file format.  If there is any checksum mismatch,
print a warning summarizing the failures to standard error.

@item --status
@opindex --status
@cindex verifying MD5 checksums
This option is useful only when verifying checksums.
When verifying checksums, don't generate the default one-line-per-file
diagnostic and don't output the warning summarizing any failures.
Failures to open or read a file still evoke individual diagnostics to
standard error.
If all listed files are readable and are consistent with the associated
MD5 checksums, exit successfully.  Otherwise exit with a status code
indicating there was a failure.

@item --tag
@opindex --tag
@cindex BSD output
Output BSD style checksums, which indicate the checksum algorithm used.
As a GNU extension, file names with problematic characters
are escaped as described above, with the same escaping indicator of @samp{\}
at the start of the line, being used.
The @option{--tag} option implies binary mode, and is disallowed with
@option{--text} mode as supporting that would unnecessarily complicate
the output format, while providing little benefit.

@item -t
@itemx --text
@opindex -t
@opindex --text
@cindex text input files
Treat each input file as text, by reading it in text mode and
outputting a @samp{ } flag.  This is the inverse of @option{--binary}.
This option is the default on systems like GNU that do not
distinguish between binary and text files.  On other systems, it is
the default for reading standard input when standard input is a
terminal.  This mode is never defaulted to if @option{--tag} is used.

@item -w
@itemx --warn
@opindex -w
@opindex --warn
@cindex verifying MD5 checksums
When verifying checksums, warn about improperly formatted MD5 checksum lines.
This option is useful only if all but a few lines in the checked input
are valid.

@item --strict
@opindex --strict
@cindex verifying MD5 checksums
When verifying checksums,
if one or more input line is invalid,
exit nonzero after all warnings have been issued.

@end table

@exitstatus


@node sha1sum invocation
@section @command{sha1sum}: Print or check SHA-1 digests

@pindex sha1sum
@cindex SHA-1
@cindex 160-bit checksum
@cindex checksum, 160-bit
@cindex fingerprint, 160-bit
@cindex message-digest, 160-bit

@command{sha1sum} computes a 160-bit checksum for each specified
@var{file}.  The usage and options of this command are precisely the
same as for @command{md5sum}.  @xref{md5sum invocation}.

Note: The SHA-1 digest is more secure than MD5, and no collisions of
it are known (different files having the same fingerprint).  However,
it is known that they can be produced with considerable, but not
unreasonable, resources.  For this reason, it is generally considered
that SHA-1 should be gradually phased out in favor of the more secure
SHA-2 hash algorithms.  @xref{sha2 utilities}.


@node sha2 utilities
@section sha2 utilities: Print or check SHA-2 digests

@pindex sha224sum
@pindex sha256sum
@pindex sha384sum
@pindex sha512sum
@cindex SHA-2
@cindex 224-bit checksum
@cindex 256-bit checksum
@cindex 384-bit checksum
@cindex 512-bit checksum
@cindex checksum, 224-bit
@cindex checksum, 256-bit
@cindex checksum, 384-bit
@cindex checksum, 512-bit
@cindex fingerprint, 224-bit
@cindex fingerprint, 256-bit
@cindex fingerprint, 384-bit
@cindex fingerprint, 512-bit
@cindex message-digest, 224-bit
@cindex message-digest, 256-bit
@cindex message-digest, 384-bit
@cindex message-digest, 512-bit

The commands @command{sha224sum}, @command{sha256sum},
@command{sha384sum} and @command{sha512sum} compute checksums of
various lengths (respectively 224, 256, 384 and 512 bits),
collectively known as the SHA-2 hashes.  The usage and options of
these commands are precisely the same as for @command{md5sum}
and @command{sha1sum}.
@xref{md5sum invocation}.


@node Operating on sorted files
@chapter Operating on sorted files

@cindex operating on sorted files
@cindex sorted files, operations on

These commands work with (or produce) sorted files.

@menu
* sort invocation::             Sort text files.
* shuf invocation::             Shuffle text files.
* uniq invocation::             Uniquify files.
* comm invocation::             Compare two sorted files line by line.
* ptx invocation::              Produce a permuted index of file contents.
* tsort invocation::            Topological sort.
@end menu


@node sort invocation
@section @command{sort}: Sort text files

@pindex sort
@cindex sorting files

@command{sort} sorts, merges, or compares all the lines from the given
files, or standard input if none are given or for a @var{file} of
@samp{-}.  By default, @command{sort} writes the results to standard
output.  Synopsis:

@example
sort [@var{option}]@dots{} [@var{file}]@dots{}
@end example

@cindex sort stability
@cindex sort's last-resort comparison
Many options affect how @command{sort} compares lines; if the results
are unexpected, try the @option{--debug} option to see what happened.
A pair of lines is compared as follows:
@command{sort} compares each pair of fields (see @option{--key}), in the
order specified on the command line, according to the associated
ordering options, until a difference is found or no fields are left.
If no key fields are specified, @command{sort} uses a default key of
the entire line.  Finally, as a last resort when all keys compare
equal, @command{sort} compares entire lines as if no ordering options
other than @option{--reverse} (@option{-r}) were specified.  The
@option{--stable} (@option{-s}) option disables this @dfn{last-resort
comparison} so that lines in which all fields compare equal are left
in their original relative order.  The @option{--unique}
(@option{-u}) option also disables the last-resort comparison.
@vindex LC_ALL
@vindex LC_COLLATE

Unless otherwise specified, all comparisons use the character collating
sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
use a non-POSIX locale (e.g., by setting @env{LC_ALL}
to @samp{en_US}), then @command{sort} may produce output that is sorted
differently than you're accustomed to.  In that case, set the @env{LC_ALL}
environment variable to @samp{C}@.  Note that setting only @env{LC_COLLATE}
has two problems.  First, it is ineffective if @env{LC_ALL} is also set.
Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
@env{LC_CTYPE} is unset) is set to an incompatible value.  For example,
you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
@env{LC_COLLATE} is @code{en_US.UTF-8}.}
A line's trailing newline is not part of the line for comparison
purposes.  If the final byte of an input file is not a newline, GNU
@command{sort} silently supplies one.  GNU @command{sort} (as
specified for all GNU utilities) has no limit on input line length or
restrictions on bytes allowed within lines.

@command{sort} has three modes of operation: sort (the default), merge,
and check for sortedness.  The following options change the operation
mode:

@table @samp

@item -c
@itemx --check
@itemx --check=diagnose-first
@opindex -c
@opindex --check
@cindex checking for sortedness
Check whether the given file is already sorted: if it is not all
sorted, print a diagnostic containing the first out-of-order line and
exit with a status of 1.
Otherwise, exit successfully.
At most one input file can be given.

@item -C
@itemx --check=quiet
@itemx --check=silent
@opindex -c
@opindex --check
@cindex checking for sortedness
Exit successfully if the given file is already sorted, and
exit with status 1 otherwise.
At most one input file can be given.
This is like @option{-c}, except it does not print a diagnostic.

@item -m
@itemx --merge
@opindex -m
@opindex --merge
@cindex merging sorted files
Merge the given files by sorting them as a group.  Each input file must
always be individually sorted.  It always works to sort instead of
merge; merging is provided because it is faster, in the case where it
works.

@end table

@cindex exit status of @command{sort}
Exit status:

@display
0 if no error occurred
1 if invoked with @option{-c} or @option{-C} and the input is not sorted
2 if an error occurred
@end display

@vindex TMPDIR
If the environment variable @env{TMPDIR} is set, @command{sort} uses its
value as the directory for temporary files instead of @file{/tmp}.  The
@option{--temporary-directory} (@option{-T}) option in turn overrides
the environment variable.

The following options affect the ordering of output lines.  They may be
specified globally or as part of a specific key field.  If no key
fields are specified, global options apply to comparison of entire
lines; otherwise the global options are inherited by key fields that do
not specify any special options of their own.  In pre-POSIX
versions of @command{sort}, global options affect only later key fields,
so portable shell scripts should specify global options first.

@table @samp

@item -b
@itemx --ignore-leading-blanks
@opindex -b
@opindex --ignore-leading-blanks
@cindex blanks, ignoring leading
@vindex LC_CTYPE
Ignore leading blanks when finding sort keys in each line.
By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
can change this.  Note blanks may be ignored by your locale's collating
rules, but without this option they will be significant for character
positions specified in keys with the @option{-k} option.

@item -d
@itemx --dictionary-order
@opindex -d
@opindex --dictionary-order
@cindex dictionary order
@cindex phone directory order
@cindex telephone directory order
@vindex LC_CTYPE
Sort in @dfn{phone directory} order: ignore all characters except
letters, digits and blanks when sorting.
By default letters and digits are those of ASCII and a blank
is a space or a tab, but the @env{LC_CTYPE} locale can change this.

@item -f
@itemx --ignore-case
@opindex -f
@opindex --ignore-case
@cindex ignoring case
@cindex case folding
@vindex LC_CTYPE
Fold lowercase characters into the equivalent uppercase characters when
comparing so that, for example, @samp{b} and @samp{B} sort as equal.
The @env{LC_CTYPE} locale determines character types.
When used with @option{--unique} those lower case equivalent lines are
thrown away.  (There is currently no way to throw away the upper case
equivalent instead.  (Any @option{--reverse} given would only affect
the final result, after the throwing away.))

@item -g
@itemx --general-numeric-sort
@itemx --sort=general-numeric
@opindex -g
@opindex --general-numeric-sort
@opindex --sort
@cindex general numeric sort
@vindex LC_NUMERIC
Sort numerically, converting a prefix of each line to a long
double-precision floating point number.  @xref{Floating point}.
Do not report overflow, underflow, or conversion errors.
Use the following collating sequence:

@itemize @bullet
@item
Lines that do not start with numbers (all considered to be equal).
@item
NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
in a consistent but machine-dependent order.
@item
Minus infinity.
@item
Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
@item
Plus infinity.
@end itemize

Use this option only if there is no alternative; it is much slower than
@option{--numeric-sort} (@option{-n}) and it can lose information when
converting to floating point.

@item -h
@itemx --human-numeric-sort
@itemx --sort=human-numeric
@opindex -h
@opindex --human-numeric-sort
@opindex --sort
@cindex human numeric sort
@vindex LC_NUMERIC
Sort numerically, first by numeric sign (negative, zero, or positive);
then by SI suffix (either empty, or @samp{k} or @samp{K}, or
one of @samp{MGTPEZY}, in that order; @pxref{Block size}); and finally
by numeric value.  For example, @samp{1023M} sorts before @samp{1G}
because @samp{M} (mega) precedes @samp{G} (giga) as an SI
suffix.  This option sorts values that are consistently scaled to the
nearest suffix, regardless of whether suffixes denote powers of 1000
or 1024, and it therefore sorts the output of any single invocation of
the @command{df}, @command{du}, or @command{ls} commands that are
invoked with their @option{--human-readable} or @option{--si} options.
The syntax for numbers is the same as for the @option{--numeric-sort}
option; the SI suffix must immediately follow the number.
Note also the @command{numfmt} command, which can be used to reformat
numbers to human format @emph{after} the sort, thus often allowing
sort to operate on more accurate numbers.

@item -i
@itemx --ignore-nonprinting
@opindex -i
@opindex --ignore-nonprinting
@cindex nonprinting characters, ignoring
@cindex unprintable characters, ignoring
@vindex LC_CTYPE
Ignore nonprinting characters.
The @env{LC_CTYPE} locale determines character types.
This option has no effect if the stronger @option{--dictionary-order}
(@option{-d}) option is also given.

@item -M
@itemx --month-sort
@itemx --sort=month
@opindex -M
@opindex --month-sort
@opindex --sort
@cindex months, sorting by
@vindex LC_TIME
An initial string, consisting of any amount of blanks, followed
by a month name abbreviation, is folded to UPPER case and
compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}@.
Invalid names compare low to valid names.  The @env{LC_TIME} locale
category determines the month spellings.
By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
can change this.

@item -n
@itemx --numeric-sort
@itemx --sort=numeric
@opindex -n
@opindex --numeric-sort
@opindex --sort
@cindex numeric sort
@vindex LC_NUMERIC
Sort numerically.  The number begins each line and consists
of optional blanks, an optional @samp{-} sign, and zero or more
digits possibly separated by thousands separators, optionally followed
by a decimal-point character and zero or more digits.  An empty
number is treated as @samp{0}.  The @env{LC_NUMERIC}
locale specifies the decimal-point character and thousands separator.
By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
can change this.

Comparison is exact; there is no rounding error.

Neither a leading @samp{+} nor exponential notation is recognized.
To compare such strings numerically, use the
@option{--general-numeric-sort} (@option{-g}) option.

@item -V
@itemx --version-sort
@opindex -V
@opindex --version-sort
@cindex version number sort
Sort by version name and number.  It behaves like a standard sort,
except that each sequence of decimal digits is treated numerically
as an index/version number.  (@xref{Details about version sort}.)

@item -r
@itemx --reverse
@opindex -r
@opindex --reverse
@cindex reverse sorting
Reverse the result of comparison, so that lines with greater key values
appear earlier in the output instead of later.

@item -R
@itemx --random-sort
@itemx --sort=random
@opindex -R
@opindex --random-sort
@opindex --sort
@cindex random sort
Sort by hashing the input keys and then sorting the hash values.
Choose the hash function at random, ensuring that it is free of
collisions so that differing keys have differing hash values.  This is
like a random permutation of the inputs (@pxref{shuf invocation}),
except that keys with the same value sort together.

If multiple random sort fields are specified, the same random hash
function is used for all fields.  To use different random hash
functions for different fields, you can invoke @command{sort} more
than once.

The choice of hash function is affected by the
@option{--random-source} option.

@end table

Other options are:

@table @samp

@item --compress-program=@var{prog}
Compress any temporary files with the program @var{prog}.

With no arguments, @var{prog} must compress standard input to standard
output, and when given the @option{-d} option it must decompress
standard input to standard output.

Terminate with an error if @var{prog} exits with nonzero status.

White space and the backslash character should not appear in
@var{prog}; they are reserved for future use.

@filesZeroFromOption{sort,,sorted output}

@item -k @var{pos1}[,@var{pos2}]
@itemx --key=@var{pos1}[,@var{pos2}]
@opindex -k
@opindex --key
@cindex sort field
Specify a sort field that consists of the part of the line between
@var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
omitted), @emph{inclusive}.

In its simplest form @var{pos} specifies a field number (starting with 1),
with fields being separated by runs of blank characters, and by default
those blanks being included in the comparison at the start of each field.
To adjust the handling of blank characters see the @option{-b} and
@option{-t} options.

More generally,
each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
where @var{f} is the number of the field to use, and @var{c} is the number
of the first character from the beginning of the field.  Fields and character
positions are numbered starting with 1; a character position of zero in
@var{pos2} indicates the field's last character.  If @samp{.@var{c}} is
omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
if omitted from @var{pos2}, it defaults to 0 (the end of the field).
@var{opts} are ordering options, allowing individual keys to be sorted
according to different rules; see below for details.  Keys can span
multiple fields.

Example:  To sort on the second field, use @option{--key=2,2}
(@option{-k 2,2}).  See below for more notes on keys and more examples.
See also the @option{--debug} option to help determine the part
of the line being used in the sort.

@item --debug
Highlight the portion of each line used for sorting.
Also issue warnings about questionable usage to stderr.

@item --batch-size=@var{nmerge}
@opindex --batch-size
@cindex number of inputs to merge, nmerge
Merge at most @var{nmerge} inputs at once.

When @command{sort} has to merge more than @var{nmerge} inputs,
it merges them in groups of @var{nmerge}, saving the result in
a temporary file, which is then used as an input in a subsequent merge.

A large value of @var{nmerge} may improve merge performance and decrease
temporary storage utilization at the expense of increased memory usage
and I/O@.  Conversely a small value of @var{nmerge} may reduce memory
requirements and I/O at the expense of temporary storage consumption and
merge performance.

The value of @var{nmerge} must be at least 2.  The default value is
currently 16, but this is implementation-dependent and may change in
the future.

The value of @var{nmerge} may be bounded by a resource limit for open
file descriptors.  The commands @samp{ulimit -n} or @samp{getconf
OPEN_MAX} may display limits for your systems; these limits may be
modified further if your program already has some files open, or if
the operating system has other limits on the number of open files.  If
the value of @var{nmerge} exceeds the resource limit, @command{sort}
silently uses a smaller value.

@item -o @var{output-file}
@itemx --output=@var{output-file}
@opindex -o
@opindex --output
@cindex overwriting of input, allowed
Write output to @var{output-file} instead of standard output.
Normally, @command{sort} reads all input before opening
@var{output-file}, so you can sort a file in place by using
commands like @code{sort -o F F} and @code{cat F | sort -o F}@.
However, it is often safer to output to an otherwise-unused file, as
data may be lost if the system crashes or @command{sort} encounters
an I/O or other serious error while a file is being sorted in place.
Also, @command{sort} with @option{--merge} (@option{-m}) can open
the output file before reading all input, so a command like @code{cat
F | sort -m -o F - G} is not safe as @command{sort} might start
writing @file{F} before @command{cat} is done reading it.

@vindex POSIXLY_CORRECT
On newer systems, @option{-o} cannot appear after an input file if
@env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}@.  Portable
scripts should specify @option{-o @var{output-file}} before any input
files.

@item --random-source=@var{file}
@opindex --random-source
@cindex random source for sorting
Use @var{file} as a source of random data used to determine which
random hash function to use with the @option{-R} option.  @xref{Random
sources}.

@item -s
@itemx --stable
@opindex -s
@opindex --stable
@cindex sort stability
@cindex sort's last-resort comparison

Make @command{sort} stable by disabling its last-resort comparison.
This option has no effect if no fields or global ordering options
other than @option{--reverse} (@option{-r}) are specified.

@item -S @var{size}
@itemx --buffer-size=@var{size}
@opindex -S
@opindex --buffer-size
@cindex size for main memory sorting
Use a main-memory sort buffer of the given @var{size}.  By default,
@var{size} is in units of 1024 bytes.  Appending @samp{%} causes
@var{size} to be interpreted as a percentage of physical memory.
Appending @samp{K} multiplies @var{size} by 1024 (the default),
@samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
@samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}@.  Appending
@samp{b} causes @var{size} to be interpreted as a byte count, with no
multiplication.

This option can improve the performance of @command{sort} by causing it
to start with a larger or smaller sort buffer than the default.
However, this option affects only the initial buffer size.  The buffer
grows beyond @var{size} if @command{sort} encounters input lines larger
than @var{size}.

@item -t @var{separator}
@itemx --field-separator=@var{separator}
@opindex -t
@opindex --field-separator
@cindex field separator character
Use character @var{separator} as the field separator when finding the
sort keys in each line.  By default, fields are separated by the empty
string between a non-blank character and a blank character.
By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
can change this.

That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
into fields @w{@samp{ foo}} and @w{@samp{ bar}}.  The field separator is
not considered to be part of either the field preceding or the field
following, so with @samp{sort @w{-t " "}} the same input line has
three fields: an empty field, @samp{foo}, and @samp{bar}.
However, fields that extend to the end of the line,
as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
retain the field separators present between the endpoints of the range.

To specify ASCII NUL as the field separator,
use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.

@item -T @var{tempdir}
@itemx --temporary-directory=@var{tempdir}
@opindex -T
@opindex --temporary-directory
@cindex temporary directory
@vindex TMPDIR
Use directory @var{tempdir} to store temporary files, overriding the
@env{TMPDIR} environment variable.  If this option is given more than
once, temporary files are stored in all the directories given.  If you
have a large sort or merge that is I/O-bound, you can often improve
performance by using this option to specify directories on different
disks and controllers.

@item --parallel=@var{n}
@opindex --parallel
@cindex multithreaded sort
Set the number of sorts run in parallel to @var{n}. By default,
@var{n} is set to the number of available processors, but limited
to 8, as there are diminishing performance gains after that.
Note also that using @var{n} threads increases the memory usage by
a factor of log @var{n}.  Also see @ref{nproc invocation}.

@item -u
@itemx --unique
@opindex -u
@opindex --unique
@cindex uniquifying output

Normally, output only the first of a sequence of lines that compare
equal.  For the @option{--check} (@option{-c} or @option{-C}) option,
check that no pair of consecutive lines compares equal.

This option also disables the default last-resort comparison.

The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
this equivalence does not extend to arbitrary @command{sort} options.
For example, @code{sort -n -u} inspects only the value of the initial
numeric string when checking for uniqueness, whereas @code{sort -n |
uniq} inspects the entire line.  @xref{uniq invocation}.

@optZeroTerminated
@macro newlineFieldSeparator
Note with @option{-z} the newline character is treated as a field separator.
@end macro

@end table

Historical (BSD and System V) implementations of @command{sort} have
differed in their interpretation of some options, particularly
@option{-b}, @option{-f}, and @option{-n}.
GNU sort follows the POSIX
behavior, which is usually (but not always!) like the System V behavior.
According to POSIX, @option{-n} no longer implies @option{-b}.  For
consistency, @option{-M} has been changed in the same way.  This may
affect the meaning of character positions in field specifications in
obscure cases.  The only fix is to add an explicit @option{-b}.

A position in a sort field specified with @option{-k} may have any
of the option letters @samp{MbdfghinRrV} appended to it, in which case no
global ordering options are inherited by that particular field.  The
@option{-b} option may be independently attached to either or both of
the start and end positions of a field specification, and if it is
inherited from the global options it will be attached to both.
If input lines can contain leading or adjacent blanks and @option{-t}
is not used, then @option{-k} is typically combined with @option{-b} or
an option that implicitly ignores leading blanks (@samp{Mghn}) as otherwise
the varying numbers of leading blanks in fields can cause confusing results.

If the start position in a sort field specifier falls after the end of
the line or after the end field, the field is empty.  If the @option{-b}
option was specified, the @samp{.@var{c}} part of a field specification
is counted from the first nonblank character of the field.

@vindex _POSIX2_VERSION
@vindex POSIXLY_CORRECT
On systems not conforming to POSIX 1003.1-2001,
@command{sort} supports a traditional origin-zero
syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
The traditional command @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}}
is equivalent to @samp{sort -k @var{a+1}.@var{x+1},@var{b}} if @var{y}
is @samp{0} or absent, otherwise it is equivalent to @samp{sort -k
@var{a+1}.@var{x+1},@var{b+1}.@var{y}}.

This traditional behavior can be controlled with the
@env{_POSIX2_VERSION} environment variable (@pxref{Standards
conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
not set by using the traditional syntax with @samp{-@var{pos2}} present.

Scripts intended for use on standard hosts should avoid traditional
syntax and should use @option{-k} instead.  For example, avoid
@samp{sort +2}, since it might be interpreted as either @samp{sort
./+2} or @samp{sort -k 3}.  If your script must also run on hosts that
support only the traditional syntax, it can use a test like @samp{if sort
-k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
to use.

Here are some examples to illustrate various combinations of options.

@itemize @bullet

@item
Sort in descending (reverse) numeric order.

@example
sort -n -r
@end example

@item
Run no more than 4 sorts concurrently, using a buffer size of 10M.

@example
sort --parallel=4 -S 10M
@end example

@item
Sort alphabetically, omitting the first and second fields
and the blanks at the start of the third field.
This uses a single key composed of the characters beginning
at the start of the first nonblank character in field three
and extending to the end of each line.

@example
sort -k 3b
@end example

@item
Sort numerically on the second field and resolve ties by sorting
alphabetically on the third and fourth characters of field five.
Use @samp{:} as the field delimiter.

@example
sort -t : -k 2,2n -k 5.3,5.4
@end example

Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
@command{sort} would have used all characters beginning in the second field
and extending to the end of the line as the primary @emph{numeric}
key.  For the large majority of applications, treating keys spanning
more than one field as numeric will not do what you expect.

Also note that the @samp{n} modifier was applied to the field-end
specifier for the first key.  It would have been equivalent to
specify @option{-k 2n,2} or @option{-k 2n,2n}.  All modifiers except
@samp{b} apply to the associated @emph{field}, regardless of whether
the modifier character is attached to the field-start and/or the
field-end part of the key specifier.

@item
Sort the password file on the fifth field and ignore any
leading blanks.  Sort lines with equal values in field five
on the numeric user ID in field three.  Fields are separated
by @samp{:}.

@example
sort -t : -k 5b,5 -k 3,3n /etc/passwd
sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
sort -t : -b -k 5,5 -k 3,3n /etc/passwd
@end example

These three commands have equivalent effect.  The first specifies that
the first key's start position ignores leading blanks and the second
key is sorted numerically.  The other two commands rely on global
options being inherited by sort keys that lack modifiers.  The inheritance
works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
equivalent, as the location of a field-end lacking a @samp{.@var{c}}
character position is not affected by whether initial blanks are
skipped.

@item
Sort a set of log files, primarily by IPv4 address and secondarily by
time stamp.  If two lines' primary and secondary keys are identical,
output the lines in the same order that they were input.  The log
files contain lines that look like this:

@example
4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
@end example

Fields are separated by exactly one space.  Sort IPv4 addresses
lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
because 61 is less than 129.

@example
sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
@end example

This example cannot be done with a single @command{sort} invocation,
since IPv4 address components are separated by @samp{.} while dates
come just after a space.  So it is broken down into two invocations of
@command{sort}: the first sorts by time stamp and the second by IPv4
address.  The time stamp is sorted by year, then month, then day, and
finally by hour-minute-second field, using @option{-k} to isolate each
field.  Except for hour-minute-second there's no need to specify the
end of each key field, since the @samp{n} and @samp{M} modifiers sort
based on leading prefixes that cannot cross field boundaries.  The
IPv4 addresses are sorted lexicographically.  The second sort uses
@samp{-s} so that ties in the primary key are broken by the secondary
key; the first sort uses @samp{-s} so that the combination of the two
sorts is stable.

@item
Generate a tags file in case-insensitive sorted order.

@smallexample
find src -type f -print0 | sort -z -f | xargs -0 etags --append
@end smallexample

The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
that file names that contain blanks or other special characters are
not broken up
by the sort operation.

@c This example is a bit contrived and needs more explanation.
@c @item
@c Sort records separated by an arbitrary string by using a pipe to convert
@c each record delimiter string to @samp{\0}, then using sort's -z option,
@c and converting each @samp{\0} back to the original record delimiter.
@c
@c @example
@c printf 'c\n\nb\n\na\n' |
@c perl -0pe 's/\n\n/\n\0/g' |
@c sort -z |
@c perl -0pe 's/\0/\n/g'
@c @end example

@item
Use the common DSU, Decorate Sort Undecorate idiom to
sort lines according to their length.

@example
awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
@end example

In general this technique can be used to sort data that the @command{sort}
command does not support, or is inefficient at, sorting directly.

@item
Shuffle a list of directories, but preserve the order of files within
each directory.  For instance, one could use this to generate a music
playlist in which albums are shuffled but the songs of each album are
played in order.

@example
ls */* | sort -t / -k 1,1R -k 2,2
@end example

@end itemize


@node shuf invocation
@section @command{shuf}: Shuffling text

@pindex shuf
@cindex shuffling files

@command{shuf} shuffles its input by outputting a random permutation
of its input lines.  Each output permutation is equally likely.
Synopses:

@example
shuf [@var{option}]@dots{} [@var{file}]
shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
@end example

@command{shuf} has three modes of operation that affect where it
obtains its input lines.  By default, it reads lines from standard
input.  The following options change the operation mode:

@table @samp

@item -e
@itemx --echo
@opindex -c
@opindex --echo
@cindex command-line operands to shuffle
Treat each command-line operand as an input line.

@item -i @var{lo}-@var{hi}
@itemx --input-range=@var{lo}-@var{hi}
@opindex -i
@opindex --input-range
@cindex input range to shuffle
Act as if input came from a file containing the range of unsigned
decimal integers @var{lo}@dots{}@var{hi}, one per line.

@end table

@command{shuf}'s other options can affect its behavior in all
operation modes:

@table @samp

@item -n @var{count}
@itemx --head-count=@var{count}
@opindex -n
@opindex --head-count
@cindex head of output
Output at most @var{count} lines.  By default, all input lines are
output.

@item -o @var{output-file}
@itemx --output=@var{output-file}
@opindex -o
@opindex --output
@cindex overwriting of input, allowed
Write output to @var{output-file} instead of standard output.
@command{shuf} reads all input before opening
@var{output-file}, so you can safely shuffle a file in place by using
commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.

@item --random-source=@var{file}
@opindex --random-source
@cindex random source for shuffling
Use @var{file} as a source of random data used to determine which
permutation to generate.  @xref{Random sources}.

@item -r
@itemx --repeat
@opindex -r
@opindex --repeat
@cindex repeat output values
Repeat output values, that is, select with replacement.  With this
option the output is not a permutation of the input; instead, each
output line is randomly chosen from all the inputs.  This option is
typically combined with @option{--head-count}; if
@option{--head-count} is not given, @command{shuf} repeats
indefinitely.

@optZeroTerminated

@end table

For example:

@example
shuf <<EOF
A man,
a plan,
a canal:
Panama!
EOF
@end example

@noindent
might produce the output

@example
Panama!
A man,
a canal:
a plan,
@end example

@noindent
Similarly, the command:

@example
shuf -e clubs hearts diamonds spades
@end example

@noindent
might output:

@example
clubs
diamonds
spades
hearts
@end example

@noindent
and the command @samp{shuf -i 1-4} might output:

@example
4
2
1
3
@end example

@noindent
The above examples all have four input lines, so @command{shuf} might
produce any of the twenty-four possible permutations of the input.  In
general, if there are @var{n} input lines, there are @var{n}! (i.e.,
@var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
output permutations.

@noindent
To output 50 random numbers each in the range 0 through 9, use:

@example
shuf -r -n 50 -i 0-9
@end example

@noindent
To simulate 100 coin flips, use:

@example
shuf -r -n 100 -e Head Tail
@end example

@exitstatus


@node uniq invocation
@section @command{uniq}: Uniquify files

@pindex uniq
@cindex uniquify files

@command{uniq} writes the unique lines in the given @file{input}, or
standard input if nothing is given or for an @var{input} name of
@samp{-}.  Synopsis:

@example
uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
@end example

By default, @command{uniq} prints its input lines, except that
it discards all but the first of adjacent repeated lines, so that
no output lines are repeated.  Optionally, it can instead discard
lines that are not repeated, or all repeated lines.

The input need not be sorted, but repeated input lines are detected
only if they are adjacent.  If you want to discard non-adjacent
duplicate lines, perhaps you want to use @code{sort -u}.
@xref{sort invocation}.

@vindex LC_COLLATE
Comparisons honor the rules specified by the @env{LC_COLLATE}
locale category.

If no @var{output} file is specified, @command{uniq} writes to standard
output.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -f @var{n}
@itemx --skip-fields=@var{n}
@opindex -f
@opindex --skip-fields
Skip @var{n} fields on each line before checking for uniqueness.  Use
a null string for comparison if a line has fewer than @var{n} fields.  Fields
are sequences of non-space non-tab characters that are separated from
each other by at least one space or tab.

For compatibility @command{uniq} supports a traditional option syntax
@option{-@var{n}}.  New scripts should use @option{-f @var{n}} instead.

@item -s @var{n}
@itemx --skip-chars=@var{n}
@opindex -s
@opindex --skip-chars
Skip @var{n} characters before checking for uniqueness.  Use a null string
for comparison if a line has fewer than @var{n} characters.  If you use both
the field and character skipping options, fields are skipped over first.

@vindex _POSIX2_VERSION
On systems not conforming to POSIX 1003.1-2001,
@command{uniq} supports a traditional option syntax
@option{+@var{n}}.
Although this traditional behavior can be controlled with the
@env{_POSIX2_VERSION} environment variable (@pxref{Standards
conformance}), portable scripts should avoid commands whose
behavior depends on this variable.
For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
the ambiguous @samp{uniq +10}.

@item -c
@itemx --count
@opindex -c
@opindex --count
Print the number of times each line occurred along with the line.

@item -i
@itemx --ignore-case
@opindex -i
@opindex --ignore-case
Ignore differences in case when comparing lines.

@item -d
@itemx --repeated
@opindex -d
@opindex --repeated
@cindex repeated lines, outputting
Discard lines that are not repeated.  When used by itself, this option
causes @command{uniq} to print the first copy of each repeated line,
and nothing else.

@item -D
@itemx --all-repeated[=@var{delimit-method}]
@opindex -D
@opindex --all-repeated
@cindex all repeated lines, outputting
Do not discard the second and subsequent repeated input lines,
but discard lines that are not repeated.
This option is useful mainly in conjunction with other options e.g.,
to ignore case or to compare only selected fields.
The optional @var{delimit-method}, supported with the long form option,
specifies how to delimit groups of repeated lines, and must be one of the
following:

@table @samp

@item none
Do not delimit groups of repeated lines.
This is equivalent to @option{--all-repeated} (@option{-D}).

@item prepend
Output a newline before each group of repeated lines.
@macro nulOutputNote
With @option{--zero-terminated} (@option{-z}), use a zero
byte (ASCII NUL) instead of a newline as the delimiter.
@end macro
@nulOutputNote

@item separate
Separate groups of repeated lines with a single newline.
This is the same as using @samp{prepend}, except that
no delimiter is inserted before the first group, and hence
may be better suited for output direct to users.
@nulOutputNote
@end table

@macro ambiguousGroupNote
Note that when groups are delimited and the input stream contains
blank lines, then the output is ambiguous.
To avoid that, filter the input through @samp{tr -s '\\n'} to
remove blank lines.
@end macro
@ambiguousGroupNote

This is a GNU extension.
@c FIXME: give an example showing *how* it's useful

@item --group[=@var{delimit-method}]
@opindex --group
@cindex all lines, grouping
Output all lines, and delimit each unique group.
@nulOutputNote
The optional @var{delimit-method} specifies how to delimit
groups, and must be one of the following:

@table @samp

@item separate
Separate unique groups with a single delimiter.
This is the default delimiting method if none is specified,
and better suited for output direct to users.

@item prepend
Output a delimiter before each group of unique items.

@item append
Output a delimiter after each group of unique items.

@item both
Output a delimiter around each group of unique items.
@end table

@ambiguousGroupNote

This is a GNU extension.

@item -u
@itemx --unique
@opindex -u
@opindex --unique
@cindex unique lines, outputting
Discard the last line that would be output for a repeated input group.
When used by itself, this option causes @command{uniq} to print unique
lines, and nothing else.

@item -w @var{n}
@itemx --check-chars=@var{n}
@opindex -w
@opindex --check-chars
Compare at most @var{n} characters on each line (after skipping any specified
fields and characters).  By default the entire rest of the lines are
compared.

@optZeroTerminated
@newlineFieldSeparator

@end table

@exitstatus


@node comm invocation
@section @command{comm}: Compare two sorted files line by line

@pindex comm
@cindex line-by-line comparison
@cindex comparing sorted files

@command{comm} writes to standard output lines that are common, and lines
that are unique, to two input files; a file name of @samp{-} means
standard input.  Synopsis:

@example
comm [@var{option}]@dots{} @var{file1} @var{file2}
@end example

@vindex LC_COLLATE
Before @command{comm} can be used, the input files must be sorted using the
collating sequence specified by the @env{LC_COLLATE} locale.
If an input file ends in a non-newline
character, a newline is silently appended.  The @command{sort} command with
no options always outputs a file that is suitable input to @command{comm}.

@cindex differing lines
@cindex common lines
With no options, @command{comm} produces three-column output.  Column one
contains lines unique to @var{file1}, column two contains lines unique
to @var{file2}, and column three contains lines common to both files.
Columns are separated by a single TAB character.
@c FIXME: when there's an option to supply an alternative separator
@c string, append "by default" to the above sentence.

@opindex -1
@opindex -2
@opindex -3
The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
the corresponding columns (and separators).  Also see @ref{Common options}.

Unlike some other comparison utilities, @command{comm} has an exit
status that does not depend on the result of the comparison.
Upon normal completion @command{comm} produces an exit code of zero.
If there is an error it exits with nonzero status.

@macro checkOrderOption{cmd}
If the @option{--check-order} option is given, unsorted inputs will
cause a fatal error message.  If the option @option{--nocheck-order}
is given, unsorted inputs will never cause an error message.  If neither
of these options is given, wrongly sorted inputs are diagnosed
only if an input file is found to contain unpairable
@ifset JOIN_COMMAND
lines, and when both input files are non empty.
@end ifset
@ifclear JOIN_COMMAND
lines.
@end ifclear
If an input file is diagnosed as being unsorted, the @command{\cmd\}
command will exit with a nonzero status (and the output should not be used).

Forcing @command{\cmd\} to process wrongly sorted input files
containing unpairable lines by specifying @option{--nocheck-order} is
not guaranteed to produce any particular output.  The output will
probably not correspond with whatever you hoped it would be.
@end macro
@checkOrderOption{comm}

@table @samp

@item --check-order
Fail with an error message if either input file is wrongly ordered.

@item --nocheck-order
Do not check that both input files are in sorted order.

Other options are:

@item --output-delimiter=@var{str}
Print @var{str} between adjacent output columns,
rather than the default of a single TAB character.

The delimiter @var{str} may not be empty.

@optZeroTerminated

@end table

@node ptx invocation
@section @command{ptx}: Produce permuted indexes

@pindex ptx

@command{ptx} reads a text file and essentially produces a permuted index, with
each keyword in its context.  The calling sketch is either one of:

@example
ptx [@var{option} @dots{}] [@var{file} @dots{}]
ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
@end example

The @option{-G} (or its equivalent: @option{--traditional}) option disables
all GNU extensions and reverts to traditional mode, thus introducing some
limitations and changing several of the program's default option values.
When @option{-G} is not specified, GNU extensions are always enabled.
GNU extensions to @command{ptx} are documented wherever appropriate in this
document.  @xref{Compatibility in ptx}, for the full list.

Individual options are explained in the following sections.

When GNU extensions are enabled, there may be zero, one or several
@var{file}s after the options.  If there is no @var{file}, the program
reads the standard input.  If there is one or several @var{file}s, they
give the name of input files which are all read in turn, as if all the
input files were concatenated.  However, there is a full contextual
break between each file and, when automatic referencing is requested,
file names and line numbers refer to individual text input files.  In
all cases, the program outputs the permuted index to the standard
output.

When GNU extensions are @emph{not} enabled, that is, when the program
operates in traditional mode, there may be zero, one or two parameters
besides the options.  If there are no parameters, the program reads the
standard input and outputs the permuted index to the standard output.
If there is only one parameter, it names the text @var{input} to be read
instead of the standard input.  If two parameters are given, they give
respectively the name of the @var{input} file to read and the name of
the @var{output} file to produce.  @emph{Be very careful} to note that,
in this case, the contents of file given by the second parameter is
destroyed.  This behavior is dictated by System V @command{ptx}
compatibility; GNU Standards normally discourage output parameters not
introduced by an option.

Note that for @emph{any} file named as the value of an option or as an
input text file, a single dash @samp{-} may be used, in which case
standard input is assumed.  However, it would not make sense to use this
convention more than once per program invocation.

@menu
* General options in ptx::      Options which affect general program behavior.
* Charset selection in ptx::    Underlying character set considerations.
* Input processing in ptx::     Input fields, contexts, and keyword selection.
* Output formatting in ptx::    Types of output format, and sizing the fields.
* Compatibility in ptx::
@end menu


@node General options in ptx
@subsection General options

@table @samp

@item -G
@itemx --traditional
As already explained, this option disables all GNU extensions to
@command{ptx} and switches to traditional mode.

@item --help
Print a short help on standard output, then exit without further
processing.

@item --version
Print the program version on standard output, then exit without further
processing.

@end table

@exitstatus


@node Charset selection in ptx
@subsection Charset selection

@c FIXME:  People don't necessarily know what an IBM-PC was these days.
As it is set up now, the program assumes that the input file is coded
using 8-bit ISO 8859-1 code, also known as Latin-1 character set,
@emph{unless} it is compiled for MS-DOS, in which case it uses the
character set of the IBM-PC@.  (GNU @command{ptx} is not known to work on
smaller MS-DOS machines anymore.)  Compared to 7-bit ASCII, the set
of characters which are letters is different; this alters the behavior
of regular expression matching.  Thus, the default regular expression
for a keyword allows foreign or diacriticized letters.  Keyword sorting,
however, is still crude; it obeys the underlying character set ordering
quite blindly.

@table @samp

@item -f
@itemx --ignore-case
@opindex -f
@opindex --ignore-case
Fold lower case letters to upper case for sorting.

@end table


@node Input processing in ptx
@subsection Word selection and input processing

@table @samp

@item -b @var{file}
@itemx --break-file=@var{file}
@opindex -b
@opindex --break-file

This option provides an alternative (to @option{-W}) method of describing
which characters make up words.  It introduces the name of a
file which contains a list of characters which can@emph{not} be part of
one word; this file is called the @dfn{Break file}.  Any character which
is not part of the Break file is a word constituent.  If both options
@option{-b} and @option{-W} are specified, then @option{-W} has precedence and
@option{-b} is ignored.

When GNU extensions are enabled, the only way to avoid newline as a
break character is to write all the break characters in the file with no
newline at all, not even at the end of the file.  When GNU extensions
are disabled, spaces, tabs and newlines are always considered as break
characters even if not included in the Break file.

@item -i @var{file}
@itemx --ignore-file=@var{file}
@opindex -i
@opindex --ignore-file

The file associated with this option contains a list of words which will
never be taken as keywords in concordance output.  It is called the
@dfn{Ignore file}.  The file contains exactly one word in each line; the
end of line separation of words is not subject to the value of the
@option{-S} option.

@item -o @var{file}
@itemx --only-file=@var{file}
@opindex -o
@opindex --only-file

The file associated with this option contains a list of words which will
be retained in concordance output; any word not mentioned in this file
is ignored.  The file is called the @dfn{Only file}.  The file contains
exactly one word in each line; the end of line separation of words is
not subject to the value of the @option{-S} option.

There is no default for the Only file.  When both an Only file and an
Ignore file are specified, a word is considered a keyword only
if it is listed in the Only file and not in the Ignore file.

@item -r
@itemx --references
@opindex -r
@opindex --references

On each input line, the leading sequence of non-white space characters will be
taken to be a reference that has the purpose of identifying this input
line in the resulting permuted index.
@xref{Output formatting in ptx},
for more information about reference production.
Using this option changes the default value for option @option{-S}.

Using this option, the program does not try very hard to remove
references from contexts in output, but it succeeds in doing so
@emph{when} the context ends exactly at the newline.  If option
@option{-r} is used with @option{-S} default value, or when GNU extensions
are disabled, this condition is always met and references are completely
excluded from the output contexts.

@item -S @var{regexp}
@itemx --sentence-regexp=@var{regexp}
@opindex -S
@opindex --sentence-regexp

This option selects which regular expression will describe the end of a
line or the end of a sentence.  In fact, this regular expression is not
the only distinction between end of lines or end of sentences, and input
line boundaries have no special significance outside this option.  By
default, when GNU extensions are enabled and if @option{-r} option is not
used, end of sentences are used.  In this case, this @var{regex} is
imported from GNU Emacs:

@example
[.?!][]\"')@}]*\\($\\|\t\\|  \\)[ \t\n]*
@end example

Whenever GNU extensions are disabled or if @option{-r} option is used, end
of lines are used; in this case, the default @var{regexp} is just:

@example
\n
@end example

Using an empty @var{regexp} is equivalent to completely disabling end of
line or end of sentence recognition.  In this case, the whole file is
considered to be a single big line or sentence.  The user might want to
disallow all truncation flag generation as well, through option @option{-F
""}.  @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
Manual}.

When the keywords happen to be near the beginning of the input line or
sentence, this often creates an unused area at the beginning of the
output context line; when the keywords happen to be near the end of the
input line or sentence, this often creates an unused area at the end of
the output context line.  The program tries to fill those unused areas
by wrapping around context in them; the tail of the input line or
sentence is used to fill the unused area on the left of the output line;
the head of the input line or sentence is used to fill the unused area
on the right of the output line.

As a matter of convenience to the user, many usual backslashed escape
sequences from the C language are recognized and converted to the
corresponding characters by @command{ptx} itself.

@item -W @var{regexp}
@itemx --word-regexp=@var{regexp}
@opindex -W
@opindex --word-regexp

This option selects which regular expression will describe each keyword.
By default, if GNU extensions are enabled, a word is a sequence of
letters; the @var{regexp} used is @samp{\w+}.  When GNU extensions are
disabled, a word is by default anything which ends with a space, a tab
or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.

An empty @var{regexp} is equivalent to not using this option.
@xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
Manual}.

As a matter of convenience to the user, many usual backslashed escape
sequences, as found in the C language, are recognized and converted to
the corresponding characters by @command{ptx} itself.

@end table


@node Output formatting in ptx
@subsection Output formatting

Output format is mainly controlled by the @option{-O} and @option{-T} options
described in the table below.  When neither @option{-O} nor @option{-T} are
selected, and if GNU extensions are enabled, the program chooses an
output format suitable for a dumb terminal.  Each keyword occurrence is
output to the center of one line, surrounded by its left and right
contexts.  Each field is properly justified, so the concordance output
can be readily observed.  As a special feature, if automatic
references are selected by option @option{-A} and are output before the
left context, that is, if option @option{-R} is @emph{not} selected, then
a colon is added after the reference; this nicely interfaces with GNU
Emacs @code{next-error} processing.  In this default output format, each
white space character, like newline and tab, is merely changed to
exactly one space, with no special attempt to compress consecutive
spaces.  This might change in the future.  Except for those white space
characters, every other character of the underlying set of 256
characters is transmitted verbatim.

Output format is further controlled by the following options.

@table @samp

@item -g @var{number}
@itemx --gap-size=@var{number}
@opindex -g
@opindex --gap-size

Select the size of the minimum white space gap between the fields on the
output line.

@item -w @var{number}
@itemx --width=@var{number}
@opindex -w
@opindex --width

Select the maximum output width of each final line.  If references are
used, they are included or excluded from the maximum output width
depending on the value of option @option{-R}@.  If this option is not
selected, that is, when references are output before the left context,
the maximum output width takes into account the maximum length of all
references.  If this option is selected, that is, when references are
output after the right context, the maximum output width does not take
into account the space taken by references, nor the gap that precedes
them.

@item -A
@itemx --auto-reference
@opindex -A
@opindex --auto-reference

Select automatic references.  Each input line will have an automatic
reference made up of the file name and the line ordinal, with a single
colon between them.  However, the file name will be empty when standard
input is being read.  If both @option{-A} and @option{-r} are selected, then
the input reference is still read and skipped, but the automatic
reference is used at output time, overriding the input reference.

@item -R
@itemx --right-side-refs
@opindex -R
@opindex --right-side-refs

In the default output format, when option @option{-R} is not used, any
references produced by the effect of options @option{-r} or @option{-A} are
placed to the far right of output lines, after the right context.  With
default output format, when the @option{-R} option is specified, references
are rather placed at the beginning of each output line, before the left
context.  For any other output format, option @option{-R} is
ignored, with one exception:  with @option{-R} the width of references
is @emph{not} taken into account in total output width given by @option{-w}.

This option is automatically selected whenever GNU extensions are
disabled.

@item -F @var{string}
@itemx --flag-truncation=@var{string}
@opindex -F
@opindex --flag-truncation

This option will request that any truncation in the output be reported
using the string @var{string}.  Most output fields theoretically extend
towards the beginning or the end of the current line, or current
sentence, as selected with option @option{-S}@.  But there is a maximum
allowed output line width, changeable through option @option{-w}, which is
further divided into space for various output fields.  When a field has
to be truncated because it cannot extend beyond the beginning or the end of
the current line to fit in, then a truncation occurs.  By default,
the string used is a single slash, as in @option{-F /}.

@var{string} may have more than one character, as in @option{-F @dots{}}.
Also, in the particular case when @var{string} is empty (@option{-F ""}),
truncation flagging is disabled, and no truncation marks are appended in
this case.

As a matter of convenience to the user, many usual backslashed escape
sequences, as found in the C language, are recognized and converted to
the corresponding characters by @command{ptx} itself.

@item -M @var{string}
@itemx --macro-name=@var{string}
@opindex -M
@opindex --macro-name

Select another @var{string} to be used instead of @samp{xx}, while
generating output suitable for @command{nroff}, @command{troff} or @TeX{}.

@item -O
@itemx --format=roff
@opindex -O
@opindex --format=roff

Choose an output format suitable for @command{nroff} or @command{troff}
processing.  Each output line will look like:

@smallexample
.xx "@var{tail}" "@var{before}" "@var{keyword_and_after}"@c
 "@var{head}" "@var{ref}"
@end smallexample

so it will be possible to write a @samp{.xx} roff macro to take care of
the output typesetting.  This is the default output format when GNU
extensions are disabled.  Option @option{-M} can be used to change
@samp{xx} to another macro name.

In this output format, each non-graphical character, like newline and
tab, is merely changed to exactly one space, with no special attempt to
compress consecutive spaces.  Each quote character @samp{"} is doubled
so it will be correctly processed by @command{nroff} or @command{troff}.

@item -T
@itemx --format=tex
@opindex -T
@opindex --format=tex

Choose an output format suitable for @TeX{} processing.  Each output
line will look like:

@smallexample
\xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@c
@{@var{after}@}@{@var{head}@}@{@var{ref}@}
@end smallexample

@noindent
so it will be possible to write a @code{\xx} definition to take care of
the output typesetting.  Note that when references are not being
produced, that is, neither option @option{-A} nor option @option{-r} is
selected, the last parameter of each @code{\xx} call is inhibited.
Option @option{-M} can be used to change @samp{xx} to another macro
name.

In this output format, some special characters, like @samp{$}, @samp{%},
@samp{&}, @samp{#} and @samp{_} are automatically protected with a
backslash.  Curly brackets @samp{@{}, @samp{@}} are protected with a
backslash and a pair of dollar signs (to force mathematical mode).  The
backslash itself produces the sequence @code{\backslash@{@}}.
Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
@code{~\@{ @}} respectively.  Other diacriticized characters of the
underlying character set produce an appropriate @TeX{} sequence as far
as possible.  The other non-graphical characters, like newline and tab,
and all other characters which are not part of ASCII, are merely
changed to exactly one space, with no special attempt to compress
consecutive spaces.  Let me know how to improve this special character
processing for @TeX{}.

@end table


@node Compatibility in ptx
@subsection The GNU extensions to @command{ptx}

This version of @command{ptx} contains a few features which do not exist in
System V @command{ptx}.  These extra features are suppressed by using the
@option{-G} command line option, unless overridden by other command line
options.  Some GNU extensions cannot be recovered by overriding, so the
simple rule is to avoid @option{-G} if you care about GNU extensions.
Here are the differences between this program and System V @command{ptx}.

@itemize @bullet

@item
This program can read many input files at once, it always writes the
resulting concordance on standard output.  On the other hand, System V
@command{ptx} reads only one file and sends the result to standard output
or, if a second @var{file} parameter is given on the command, to that
@var{file}.

Having output parameters not introduced by options is a dangerous
practice which GNU avoids as far as possible.  So, for using @command{ptx}
portably between GNU and System V, you should always use it with a
single input file, and always expect the result on standard output.  You
might also want to automatically configure in a @option{-G} option to
@command{ptx} calls in products using @command{ptx}, if the configurator finds
that the installed @command{ptx} accepts @option{-G}.

@item
The only options available in System V @command{ptx} are options @option{-b},
@option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
@option{-w}.  All other options are GNU extensions and are not repeated in
this enumeration.  Moreover, some options have a slightly different
meaning when GNU extensions are enabled, as explained below.

@item
By default, concordance output is not formatted for @command{troff} or
@command{nroff}.  It is rather formatted for a dumb terminal.  @command{troff}
or @command{nroff} output may still be selected through option @option{-O}.

@item
Unless @option{-R} option is used, the maximum reference width is
subtracted from the total output line width.  With GNU extensions
disabled, width of references is not taken into account in the output
line width computations.

@item
All 256 bytes, even ASCII NUL bytes, are always read and
processed from input file with no adverse effect, even if GNU extensions
are disabled.  However, System V @command{ptx} does not accept 8-bit
characters, a few control characters are rejected, and the tilde
@samp{~} is also rejected.

@item
Input line length is only limited by available memory, even if GNU
extensions are disabled.  However, System V @command{ptx} processes only
the first 200 characters in each line.

@item
The break (non-word) characters default to be every character except all
letters of the underlying character set, diacriticized or not.  When GNU
extensions are disabled, the break characters default to space, tab and
newline only.

@item
The program makes better use of output line width.  If GNU extensions
are disabled, the program rather tries to imitate System V @command{ptx},
but still, there are some slight disposition glitches this program does
not completely reproduce.

@item
The user can specify both an Ignore file and an Only file.  This is not
allowed with System V @command{ptx}.

@end itemize


@node tsort invocation
@section @command{tsort}: Topological sort

@pindex tsort
@cindex topological sort

@command{tsort} performs a topological sort on the given @var{file}, or
standard input if no input file is given or for a @var{file} of
@samp{-}.  For more details and some history, see @ref{tsort background}.
Synopsis:

@example
tsort [@var{option}] [@var{file}]
@end example

@command{tsort} reads its input as pairs of strings, separated by blanks,
indicating a partial ordering.  The output is a total ordering that
corresponds to the given partial ordering.

For example

@example
tsort <<EOF
a b c
d
e f
b c d e
EOF
@end example

@noindent
will produce the output

@example
a
b
c
d
e
f
@end example

Consider a more realistic example.
You have a large set of functions all in one file, and they may all be
declared static except one.  Currently that one (say @code{main}) is the
first function defined in the file, and the ones it calls directly follow
it, followed by those they call, etc.  Let's say that you are determined
to take advantage of prototypes, so you have to choose between declaring
all of those functions (which means duplicating a lot of information from
the definitions) and rearranging the functions so that as many as possible
are defined before they are used.  One way to automate the latter process
is to get a list for each function of the functions it calls directly.
Many programs can generate such lists.  They describe a call graph.
Consider the following list, in which a given line indicates that the
function on the left calls the one on the right directly.

@example
main parse_options
main tail_file
main tail_forever
tail_file pretty_name
tail_file write_header
tail_file tail
tail_forever recheck
tail_forever pretty_name
tail_forever write_header
tail_forever dump_remainder
tail tail_lines
tail tail_bytes
tail_lines start_lines
tail_lines dump_remainder
tail_lines file_lines
tail_lines pipe_lines
tail_bytes xlseek
tail_bytes start_bytes
tail_bytes dump_remainder
tail_bytes pipe_bytes
file_lines dump_remainder
recheck pretty_name
@end example

then you can use @command{tsort} to produce an ordering of those
functions that satisfies your requirement.

@example
example$ tsort call-graph | tac
dump_remainder
start_lines
file_lines
pipe_lines
xlseek
start_bytes
pipe_bytes
tail_lines
tail_bytes
pretty_name
write_header
tail
recheck
parse_options
tail_file
tail_forever
main
@end example

@command{tsort} detects any cycles in the input and writes the first cycle
encountered to standard error.

Note that for a given partial ordering, generally there is no unique
total ordering.  In the context of the call graph above, the function
@code{parse_options} may be placed anywhere in the list as long as it
precedes @code{main}.

The only options are @option{--help} and @option{--version}.  @xref{Common
options}.

@exitstatus

@menu
* tsort background::            Where tsort came from.
@end menu

@node tsort background
@subsection @command{tsort}: Background

@command{tsort} exists because very early versions of the Unix linker processed
an archive file exactly once, and in order.  As @command{ld} read each object
in the archive, it decided whether it was needed in the program based on
whether it defined any symbols which were undefined at that point in
the link.

This meant that dependencies within the archive had to be handled
specially.  For example, @code{scanf} probably calls @code{read}.  That means
that in a single pass through an archive, it was important for @code{scanf.o}
to appear before read.o, because otherwise a program which calls
@code{scanf} but not @code{read} might end up with an unexpected unresolved
reference to @code{read}.

The way to address this problem was to first generate a set of
dependencies of one object file on another.  This was done by a shell
script called @command{lorder}.  The GNU tools don't provide a version of
lorder, as far as I know, but you can still find it in BSD
distributions.

Then you ran @command{tsort} over the @command{lorder} output, and you used the
resulting sort to define the order in which you added objects to the archive.

This whole procedure has been obsolete since about 1980, because
Unix archives now contain a symbol table (traditionally built by
@command{ranlib}, now generally built by @command{ar} itself), and the Unix
linker uses the symbol table to effectively make multiple passes over
an archive file.

Anyhow, that's where tsort came from.  To solve an old problem with
the way the linker handled archive files, which has since been solved
in different ways.


@node Operating on fields
@chapter Operating on fields

@menu
* cut invocation::              Print selected parts of lines.
* paste invocation::            Merge lines of files.
* join invocation::             Join lines on a common field.
@end menu


@node cut invocation
@section @command{cut}: Print selected parts of lines

@pindex cut
@command{cut} writes to standard output selected parts of each line of each
input file, or standard input if no files are given or for a file name of
@samp{-}.  Synopsis:

@example
cut @var{option}@dots{} [@var{file}]@dots{}
@end example

In the table which follows, the @var{byte-list}, @var{character-list},
and @var{field-list} are one or more numbers or ranges (two numbers
separated by a dash) separated by commas.  Bytes, characters, and
fields are numbered starting at 1.  Incomplete ranges may be
given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
@samp{@var{n}} through end of line or last field.  The list elements
can be repeated, can overlap, and can be specified in any order; but
the selected input is written in the same order that it is read, and
is written exactly once.

The program accepts the following options.  Also see @ref{Common
options}.

@table @samp

@item -b @var{byte-list}
@itemx --bytes=@var{byte-list}
@opindex -b
@opindex --bytes
Select for printing only the bytes in positions listed in
@var{byte-list}.  Tabs and backspaces are treated like any other
character; they take up 1 byte.  If an output delimiter is specified,
(see the description of @option{--output-delimiter}), then output that
string between ranges of selected bytes.

@item -c @var{character-list}
@itemx --characters=@var{character-list}
@opindex -c
@opindex --characters
Select for printing only the characters in positions listed in
@var{character-list}.  The same as @option{-b} for now, but
internationalization will change that.  Tabs and backspaces are
treated like any other character; they take up 1 character.  If an
output delimiter is specified, (see the description of
@option{--output-delimiter}), then output that string between ranges
of selected bytes.

@item -f @var{field-list}
@itemx --fields=@var{field-list}
@opindex -f
@opindex --fields
Select for printing only the fields listed in @var{field-list}.
Fields are separated by a TAB character by default.  Also print any
line that contains no delimiter character, unless the
@option{--only-delimited} (@option{-s}) option is specified.

Note @command{awk} supports more sophisticated field processing,
and by default will use (and discard) runs of blank characters to
separate fields, and ignore leading and trailing blanks.
@example
@verbatim
awk '{print $2}'    # print the second field
awk '{print $NF-1}' # print the penultimate field
awk '{print $2,$1}' # reorder the first two fields
@end verbatim
@end example

In the unlikely event that @command{awk} is unavailable,
one can use the @command{join} command, to process blank
characters as @command{awk} does above.
@example
@verbatim
join -a1 -o 1.2     - /dev/null # print the second field
join -a1 -o 1.2,1.1 - /dev/null # reorder the first two fields
@end verbatim
@end example

@item -d @var{input_delim_byte}
@itemx --delimiter=@var{input_delim_byte}
@opindex -d
@opindex --delimiter
With @option{-f}, use the first byte of @var{input_delim_byte} as
the input fields separator (default is TAB).

@item -n
@opindex -n
Do not split multi-byte characters (no-op for now).

@item -s
@itemx --only-delimited
@opindex -s
@opindex --only-delimited
For @option{-f}, do not print lines that do not contain the field separator
character.  Normally, any line without a field separator is printed verbatim.

@item --output-delimiter=@var{output_delim_string}
@opindex --output-delimiter
With @option{-f}, output fields are separated by @var{output_delim_string}.
The default with @option{-f} is to use the input delimiter.
When using @option{-b} or @option{-c} to select ranges of byte or
character offsets (as opposed to ranges of fields),
output @var{output_delim_string} between non-overlapping
ranges of selected bytes.

@item --complement
@opindex --complement
This option is a GNU extension.
Select for printing the complement of the bytes, characters or fields
selected with the @option{-b}, @option{-c} or @option{-f} options.
In other words, do @emph{not} print the bytes, characters or fields
specified via those options.  This option is useful when you have
many fields and want to print all but a few of them.

@optZeroTerminated

@end table

@exitstatus


@node paste invocation
@section @command{paste}: Merge lines of files

@pindex paste
@cindex merging files

@command{paste} writes to standard output lines consisting of sequentially
corresponding lines of each given file, separated by a TAB character.
Standard input is used for a file name of @samp{-} or if no input files
are given.

Synopsis:

@example
paste [@var{option}]@dots{} [@var{file}]@dots{}
@end example

For example, with:
@example
$ cat num2
1
2
$ cat let3
a
b
c
@end example

Take lines sequentially from each file:
@example
$ paste num2 let3
1       a
2       b
       @ c
@end example

Duplicate lines from a file:
@example
$ paste num2 let3 num2
1       a      1
2       b      2
       @ c
@end example

Intermix lines from stdin:
@example
$ paste - let3 - < num2
1       a      2
       @ b
       @ c
@end example

Join consecutive lines with a space:
@example
$ seq 4 | paste -d ' ' - -
1 2
3 4
@end example

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -s
@itemx --serial
@opindex -s
@opindex --serial
Paste the lines of one file at a time rather than one line from each
file.  Using the above example data:

@example
$ paste -s num2 let3
1       2
a       b       c
@end example

@item -d @var{delim-list}
@itemx --delimiters=@var{delim-list}
@opindex -d
@opindex --delimiters
Consecutively use the characters in @var{delim-list} instead of
TAB to separate merged lines.  When @var{delim-list} is
exhausted, start again at its beginning.  Using the above example data:

@example
$ paste -d '%_' num2 let3 num2
1%a_1
2%b_2
%c_
@end example

@optZeroTerminated

@end table

@exitstatus


@node join invocation
@section @command{join}: Join lines on a common field

@pindex join
@cindex common field, joining on

@command{join} writes to standard output a line for each pair of input
lines that have identical join fields.  Synopsis:

@example
join [@var{option}]@dots{} @var{file1} @var{file2}
@end example

Either @var{file1} or @var{file2} (but not both) can be @samp{-},
meaning standard input.  @var{file1} and @var{file2} should be
sorted on the join fields.

@vindex LC_COLLATE
Normally, the sort order is that of the
collating sequence specified by the @env{LC_COLLATE} locale.  Unless
the @option{-t} option is given, the sort comparison ignores blanks at
the start of the join field, as in @code{sort -b}.  If the
@option{--ignore-case} option is given, the sort comparison ignores
the case of characters in the join field, as in @code{sort -f}.

The @command{sort} and @command{join} commands should use consistent
locales and options if the output of @command{sort} is fed to
@command{join}.  You can use a command like @samp{sort -k 1b,1} to
sort a file on its default join field, but if you select a non-default
locale, join field, separator, or comparison options, then you should
do so consistently between @command{join} and @command{sort}.
If @samp{join -t ''} is specified then the whole line is considered which
matches the default operation of sort.

If the input has no unpairable lines, a GNU extension is
available; the sort order can be any order that considers two fields
to be equal if and only if the sort comparison described above
considers them to be equal.  For example:

@example
$ cat file1
a a1
c c1
b b1
$ cat file2
a a2
c c2
b b2
$ join file1 file2
a a1 a2
c c1 c2
b b1 b2
@end example

@set JOIN_COMMAND
@checkOrderOption{join}
@clear JOIN_COMMAND

The defaults are:
@itemize
@item the join field is the first field in each line;
@item fields in the input are separated by one or more blanks, with leading
blanks on the line ignored;
@item fields in the output are separated by a space;
@item each output line consists of the join field, the remaining
fields from @var{file1}, then the remaining fields from @var{file2}.
@end itemize

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -a @var{file-number}
@opindex -a
Print a line for each unpairable line in file @var{file-number} (either
@samp{1} or @samp{2}), in addition to the normal output.

@item --check-order
Fail with an error message if either input file is wrongly ordered.

@item --nocheck-order
Do not check that both input files are in sorted order.  This is the default.

@item -e @var{string}
@opindex -e
Replace those output fields that are missing in the input with @var{string}.
I.e., missing fields specified with the @option{-12jo} options.

@item --header
@opindex --header
Treat the first line of each input file as a header line.  The header lines
will be joined and printed as the first output line.  If @option{-o} is used to
specify output format, the header line will be printed according to the
specified format.  The header lines will not be checked for ordering even if
@option{--check-order} is specified.  Also if the header lines from each file
do not match, the heading fields from the first file will be used.

@item -i
@itemx --ignore-case
@opindex -i
@opindex --ignore-case
Ignore differences in case when comparing keys.
With this option, the lines of the input files must be ordered in the same way.
Use @samp{sort -f} to produce this ordering.

@item -1 @var{field}
@opindex -1
Join on field @var{field} (a positive integer) of file 1.

@item -2 @var{field}
@opindex -2
Join on field @var{field} (a positive integer) of file 2.

@item -j @var{field}
Equivalent to @option{-1 @var{field} -2 @var{field}}.

@item -o @var{field-list}
@itemx -o auto
If the keyword @samp{auto} is specified, infer the output format from
the first line in each file.  This is the same as the default output format
but also ensures the same number of fields are output for each line.
Missing fields are replaced with the @option{-e} option and extra fields
are discarded.

Otherwise, construct each output line according to the format in
@var{field-list}.  Each element in @var{field-list} is either the single
character @samp{0} or has the form @var{m.n} where the file number, @var{m},
is @samp{1} or @samp{2} and @var{n} is a positive field number.

A field specification of @samp{0} denotes the join field.
In most cases, the functionality of the @samp{0} field spec
may be reproduced using the explicit @var{m.n} that corresponds
to the join field.  However, when printing unpairable lines
(using either of the @option{-a} or @option{-v} options), there is no way
to specify the join field using @var{m.n} in @var{field-list}
if there are unpairable lines in both files.
To give @command{join} that functionality, POSIX invented the @samp{0}
field specification notation.

The elements in @var{field-list}
are separated by commas or blanks.
Blank separators typically need to be quoted for the shell.  For
example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
2.2'} are equivalent.

All output lines---including those printed because of any -a or -v
option---are subject to the specified @var{field-list}.

@item -t @var{char}
Use character @var{char} as the input and output field separator.
Treat as significant each occurrence of @var{char} in the input file.
Use @samp{sort -t @var{char}}, without the @option{-b} option of
@samp{sort}, to produce this ordering.  If @samp{join -t ''} is specified,
the whole line is considered, matching the default operation of sort.
If @samp{-t '\0'} is specified then the ASCII NUL
character is used to delimit the fields.

@item -v @var{file-number}
Print a line for each unpairable line in file @var{file-number}
(either @samp{1} or @samp{2}), instead of the normal output.

@optZeroTerminated
@newlineFieldSeparator

@end table

@exitstatus


@node Operating on characters
@chapter Operating on characters

@cindex operating on characters

These commands operate on individual characters.

@menu
* tr invocation::               Translate, squeeze, and/or delete characters.
* expand invocation::           Convert tabs to spaces.
* unexpand invocation::         Convert spaces to tabs.
@end menu


@node tr invocation
@section @command{tr}: Translate, squeeze, and/or delete characters

@pindex tr

Synopsis:

@example
tr [@var{option}]@dots{} @var{set1} [@var{set2}]
@end example

@command{tr} copies standard input to standard output, performing
one of the following operations:

@itemize @bullet
@item
translate, and optionally squeeze repeated characters in the result,
@item
squeeze repeated characters,
@item
delete characters,
@item
delete characters, then squeeze repeated characters from the result.
@end itemize

The @var{set1} and (if given) @var{set2} arguments define ordered
sets of characters, referred to below as @var{set1} and @var{set2}.  These
sets are the characters of the input that @command{tr} operates on.
The @option{--complement} (@option{-c}, @option{-C}) option replaces
@var{set1} with its
complement (all of the characters that are not in @var{set1}).

Currently @command{tr} fully supports only single-byte characters.
Eventually it will support multibyte characters; when it does, the
@option{-C} option will cause it to complement the set of characters,
whereas @option{-c} will cause it to complement the set of values.
This distinction will matter only when some values are not characters,
and this is possible only in locales using multibyte encodings when
the input contains encoding errors.

The program accepts the @option{--help} and @option{--version}
options.  @xref{Common options}.  Options must precede operands.

@exitstatus

@menu
* Character sets::              Specifying sets of characters.
* Translating::                 Changing one set of characters to another.
* Squeezing and deleting::      Removing characters.
@end menu


@node Character sets
@subsection Specifying sets of characters

@cindex specifying sets of characters

The format of the @var{set1} and @var{set2} arguments resembles
the format of regular expressions; however, they are not regular
expressions, only lists of characters.  Most characters simply
represent themselves in these strings, but the strings can contain
the shorthands listed below, for convenience.  Some of them can be
used only in @var{set1} or @var{set2}, as noted below.

@table @asis

@item Backslash escapes
@cindex backslash escapes

The following backslash escape sequences are recognized:

@table @samp
@item \a
Control-G.
@item \b
Control-H.
@item \f
Control-L.
@item \n
Control-J.
@item \r
Control-M.
@item \t
Control-I.
@item \v
Control-K.
@item \@var{ooo}
The 8-bit character with the value given by @var{ooo}, which is 1 to 3
octal digits.  Note that @samp{\400} is interpreted as the two-byte
sequence, @samp{\040} @samp{0}.
@item \\
A backslash.
@end table

While a backslash followed by a character not listed above is
interpreted as that character, the backslash also effectively
removes any special significance, so it is useful to escape
@samp{[}, @samp{]}, @samp{*}, and @samp{-}.

@item Ranges
@cindex ranges

The notation @samp{@var{m}-@var{n}} expands to all of the characters
from @var{m} through @var{n}, in ascending order.  @var{m} should
collate before @var{n}; if it doesn't, an error results.  As an example,
@samp{0-9} is the same as @samp{0123456789}.

GNU @command{tr} does not support the System V syntax that uses square
brackets to enclose ranges.  Translations specified in that format
sometimes work as expected, since the brackets are often transliterated
to themselves.  However, they should be avoided because they sometimes
behave unexpectedly.  For example, @samp{tr -d '[0-9]'} deletes brackets
as well as digits.

Many historically common and even accepted uses of ranges are not
portable.  For example, on EBCDIC hosts using the @samp{A-Z}
range will not do what most would expect because @samp{A} through @samp{Z}
are not contiguous as they are in ASCII@.
If you can rely on a POSIX compliant version of @command{tr}, then
the best way to work around this is to use character classes (see below).
Otherwise, it is most portable (and most ugly) to enumerate the members
of the ranges.

@item Repeated characters
@cindex repeated characters

The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
copies of character @var{c}.  Thus, @samp{[y*6]} is the same as
@samp{yyyyyy}.  The notation @samp{[@var{c}*]} in @var{string2} expands
to as many copies of @var{c} as are needed to make @var{set2} as long as
@var{set1}.  If @var{n} begins with @samp{0}, it is interpreted in
octal, otherwise in decimal.

@item Character classes
@cindex character classes

The notation @samp{[:@var{class}:]} expands to all of the characters in
the (predefined) class @var{class}.  The characters expand in no
particular order, except for the @code{upper} and @code{lower} classes,
which expand in ascending order.  When the @option{--delete} (@option{-d})
and @option{--squeeze-repeats} (@option{-s}) options are both given, any
character class can be used in @var{set2}.  Otherwise, only the
character classes @code{lower} and @code{upper} are accepted in
@var{set2}, and then only if the corresponding character class
(@code{upper} and @code{lower}, respectively) is specified in the same
relative position in @var{set1}.  Doing this specifies case conversion.
The class names are given below; an error results when an invalid class
name is given.

@table @code
@item alnum
@opindex alnum
Letters and digits.
@item alpha
@opindex alpha
Letters.
@item blank
@opindex blank
Horizontal whitespace.
@item cntrl
@opindex cntrl
Control characters.
@item digit
@opindex digit
Digits.
@item graph
@opindex graph
Printable characters, not including space.
@item lower
@opindex lower
Lowercase letters.
@item print
@opindex print
Printable characters, including space.
@item punct
@opindex punct
Punctuation characters.
@item space
@opindex space
Horizontal or vertical whitespace.
@item upper
@opindex upper
Uppercase letters.
@item xdigit
@opindex xdigit
Hexadecimal digits.
@end table

@item Equivalence classes
@cindex equivalence classes

The syntax @samp{[=@var{c}=]} expands to all of the characters that are
equivalent to @var{c}, in no particular order.  Equivalence classes are
a relatively recent invention intended to support non-English alphabets.
But there seems to be no standard way to define them or determine their
contents.  Therefore, they are not fully implemented in GNU @command{tr};
each character's equivalence class consists only of that character,
which is of no particular use.

@end table


@node Translating
@subsection Translating

@cindex translating characters

@command{tr} performs translation when @var{set1} and @var{set2} are
both given and the @option{--delete} (@option{-d}) option is not given.
@command{tr} translates each character of its input that is in @var{set1}
to the corresponding character in @var{set2}.  Characters not in
@var{set1} are passed through unchanged.  When a character appears more
than once in @var{set1} and the corresponding characters in @var{set2}
are not all the same, only the final one is used.  For example, these
two commands are equivalent:

@example
tr aaa xyz
tr a z
@end example

A common use of @command{tr} is to convert lowercase characters to
uppercase.  This can be done in many ways.  Here are three of them:

@example
tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
tr a-z A-Z
tr '[:lower:]' '[:upper:]'
@end example

@noindent
But note that using ranges like @code{a-z} above is not portable.

When @command{tr} is performing translation, @var{set1} and @var{set2}
typically have the same length.  If @var{set1} is shorter than
@var{set2}, the extra characters at the end of @var{set2} are ignored.

On the other hand, making @var{set1} longer than @var{set2} is not
portable; POSIX says that the result is undefined.  In this situation,
BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
the last character of @var{set2} as many times as necessary.  System V
@command{tr} truncates @var{set1} to the length of @var{set2}.

By default, GNU @command{tr} handles this case like BSD @command{tr}.
When the @option{--truncate-set1} (@option{-t}) option is given,
GNU @command{tr} handles this case like the System V @command{tr}
instead.  This option is ignored for operations other than translation.

Acting like System V @command{tr} in this case breaks the relatively common
BSD idiom:

@example
tr -cs A-Za-z0-9 '\012'
@end example

@noindent
because it converts only zero bytes (the first element in the
complement of @var{set1}), rather than all non-alphanumerics, to
newlines.

@noindent
By the way, the above idiom is not portable because it uses ranges, and
it assumes that the octal code for newline is 012.
Assuming a POSIX compliant @command{tr}, here is a better
way to write it:

@example
tr -cs '[:alnum:]' '[\n*]'
@end example


@node Squeezing and deleting
@subsection Squeezing repeats and deleting

@cindex squeezing repeat characters
@cindex deleting characters
@cindex removing characters

When given just the @option{--delete} (@option{-d}) option, @command{tr}
removes any input characters that are in @var{set1}.

When given just the @option{--squeeze-repeats} (@option{-s}) option
and not translating, @command{tr} replaces each input sequence of a
repeated character that is in @var{set1} with a single occurrence of
that character.

When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
first performs any deletions using @var{set1}, then squeezes repeats
from any remaining characters using @var{set2}.

The @option{--squeeze-repeats} option may also be used when translating,
in which case @command{tr} first performs translation, then squeezes
repeats from any remaining characters using @var{set2}.

Here are some examples to illustrate various combinations of options:

@itemize @bullet

@item
Remove all zero bytes:

@example
tr -d '\0'
@end example

@item
Put all words on lines by themselves.  This converts all
non-alphanumeric characters to newlines, then squeezes each string
of repeated newlines into a single newline:

@example
tr -cs '[:alnum:]' '[\n*]'
@end example

@item
Convert each sequence of repeated newlines to a single newline.
I.e., delete blank lines:

@example
tr -s '\n'
@end example

@item
Find doubled occurrences of words in a document.
@c Separate the following two "the"s, so typo checkers don't complain.
For example, people often write ``the @w{}the'' with the repeated words
separated by a newline.  The Bourne shell script below works first
by converting each sequence of punctuation and blank characters to a
single newline.  That puts each ``word'' on a line by itself.
Next it maps all uppercase characters to lower case, and finally it
runs @command{uniq} with the @option{-d} option to print out only the words
that were repeated.

@example
#!/bin/sh
cat -- "$@@" \
  | tr -s '[:punct:][:blank:]' '[\n*]' \
  | tr '[:upper:]' '[:lower:]' \
  | uniq -d
@end example

@item
Deleting a small set of characters is usually straightforward.  For example,
to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:

@example
tr -d axM
@end example

However, when @samp{-} is one of those characters, it can be tricky because
@samp{-} has special meanings.  Performing the same task as above but also
removing all @samp{-} characters, we might try @code{tr -d -axM}, but
that would fail because @command{tr} would try to interpret @option{-a} as
a command-line option.  Alternatively, we could try putting the hyphen
inside the string, @code{tr -d a-xM}, but that wouldn't work either because
it would make @command{tr} interpret @code{a-x} as the range of characters
@samp{a}@dots{}@samp{x} rather than the three.
One way to solve the problem is to put the hyphen at the end of the list
of characters:

@example
tr -d axM-
@end example

Or you can use @samp{--} to terminate option processing:

@example
tr -d -- -axM
@end example

More generally, use the character class notation @code{[=c=]}
with @samp{-} (or any other character) in place of the @samp{c}:

@example
tr -d '[=-=]axM'
@end example

Note how single quotes are used in the above example to protect the
square brackets from interpretation by a shell.

@end itemize


@node expand invocation
@section @command{expand}: Convert tabs to spaces

@pindex expand
@cindex tabs to spaces, converting
@cindex converting tabs to spaces

@command{expand} writes the contents of each given @var{file}, or standard
input if none are given or for a @var{file} of @samp{-}, to standard
output, with tab characters converted to the appropriate number of
spaces.  Synopsis:

@example
expand [@var{option}]@dots{} [@var{file}]@dots{}
@end example

By default, @command{expand} converts all tabs to spaces.  It preserves
backspace characters in the output; they decrement the column count for
tab calculations.  The default action is equivalent to @option{-t 8} (set
tabs every 8 columns).

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -t @var{tab1}[,@var{tab2}]@dots{}
@itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
@opindex -t
@opindex --tabs
@cindex tab stops, setting
If only one tab stop is given, set the tabs @var{tab1} spaces apart
(default is 8).  Otherwise, set the tabs at columns @var{tab1},
@var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
last tab stop given with single spaces.  Tab stops can be separated by
blanks as well as by commas.

For compatibility, GNU @command{expand} also accepts the obsolete
option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}.  New scripts
should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.

@item -i
@itemx --initial
@opindex -i
@opindex --initial
@cindex initial tabs, converting
Only convert initial tabs (those that precede all non-space or non-tab
characters) on each line to spaces.

@end table

@exitstatus


@node unexpand invocation
@section @command{unexpand}: Convert spaces to tabs

@pindex unexpand

@command{unexpand} writes the contents of each given @var{file}, or
standard input if none are given or for a @var{file} of @samp{-}, to
standard output, converting blanks at the beginning of each line into
as many tab characters as needed.  In the default POSIX
locale, a @dfn{blank} is a space or a tab; other locales may specify
additional blank characters.  Synopsis:

@example
unexpand [@var{option}]@dots{} [@var{file}]@dots{}
@end example

By default, @command{unexpand} converts only initial blanks (those
that precede all non-blank characters) on each line.  It
preserves backspace characters in the output; they decrement the column
count for tab calculations.  By default, tabs are set at every 8th
column.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -t @var{tab1}[,@var{tab2}]@dots{}
@itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
@opindex -t
@opindex --tabs
If only one tab stop is given, set the tabs @var{tab1} columns apart
instead of the default 8.  Otherwise, set the tabs at columns
@var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
beyond the tab stops given unchanged.  Tab stops can be separated by
blanks as well as by commas.  This option implies the @option{-a} option.

For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
@option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
separated by commas.  (Unlike @option{-t}, this obsolete option does
not imply @option{-a}.)  New scripts should use @option{--first-only -t
@var{tab1}[,@var{tab2}]@dots{}} instead.

@item -a
@itemx --all
@opindex -a
@opindex --all
Also convert all sequences of two or more blanks just before a tab stop,
even if they occur after non-blank characters in a line.

@end table

@exitstatus


@node Directory listing
@chapter Directory listing

This chapter describes the @command{ls} command and its variants @command{dir}
and @command{vdir}, which list information about files.

@menu
* ls invocation::               List directory contents.
* dir invocation::              Briefly ls.
* vdir invocation::             Verbosely ls.
* dircolors invocation::        Color setup for ls, etc.
@end menu


@node ls invocation
@section @command{ls}: List directory contents

@pindex ls
@cindex directory listing

The @command{ls} program lists information about files (of any type,
including directories).  Options and file arguments can be intermixed
arbitrarily, as usual.

For non-option command-line arguments that are directories, by default
@command{ls} lists the contents of directories, not recursively, and
omitting files with names beginning with @samp{.}.  For other non-option
arguments, by default @command{ls} lists just the file name.  If no
non-option argument is specified, @command{ls} operates on the current
directory, acting as if it had been invoked with a single argument of @samp{.}.

@vindex LC_ALL
By default, the output is sorted alphabetically, according to the locale
settings in effect.@footnote{If you use a non-POSIX
locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
produce output that is sorted differently than you're accustomed to.
In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
If standard output is
a terminal, the output is in columns (sorted vertically) and control
characters are output as question marks; otherwise, the output is listed
one per line and control characters are output as-is.

Because @command{ls} is such a fundamental program, it has accumulated many
options over the years.  They are described in the subsections below;
within each section, options are listed alphabetically (ignoring case).
The division of options into the subsections is not absolute, since some
options affect more than one aspect of @command{ls}'s operation.

@cindex exit status of @command{ls}
Exit status:

@display
0 success
1 minor problems  (e.g., failure to access a file or directory not
  specified as a command line argument.  This happens when listing a
  directory in which entries are actively being removed or renamed.)
2 serious trouble (e.g., memory exhausted, invalid option, failure
  to access a file or directory specified as a command line argument
  or a directory loop)
@end display

Also see @ref{Common options}.

@menu
* Which files are listed::
* What information is listed::
* Sorting the output::
* Details about version sort::
* General output formatting::
* Formatting file timestamps::
* Formatting the file names::
@end menu


@node Which files are listed
@subsection Which files are listed

These options determine which files @command{ls} lists information for.
By default, @command{ls} lists files and the contents of any
directories on the command line, except that in directories it ignores
files whose names start with @samp{.}.

@table @samp

@item -a
@itemx --all
@opindex -a
@opindex --all
In directories, do not ignore file names that start with @samp{.}.

@item -A
@itemx --almost-all
@opindex -A
@opindex --almost-all
In directories, do not ignore all file names that start with @samp{.};
ignore only @file{.} and @file{..}.  The @option{--all} (@option{-a})
option overrides this option.

@item -B
@itemx --ignore-backups
@opindex -B
@opindex --ignore-backups
@cindex backup files, ignoring
In directories, ignore files that end with @samp{~}.  This option is
equivalent to @samp{--ignore='*~' --ignore='.*~'}.

@item -d
@itemx --directory
@opindex -d
@opindex --directory
List just the names of directories, as with other types of files, rather
than listing their contents.
@c The following sentence is the same as the one for -F.
Do not follow symbolic links listed on the
command line unless the @option{--dereference-command-line} (@option{-H}),
@option{--dereference} (@option{-L}), or
@option{--dereference-command-line-symlink-to-dir} options are specified.

@item -H
@itemx --dereference-command-line
@opindex -H
@opindex --dereference-command-line
@cindex symbolic links, dereferencing
If a command line argument specifies a symbolic link, show information
for the file the link references rather than for the link itself.

@item --dereference-command-line-symlink-to-dir
@opindex --dereference-command-line-symlink-to-dir
@cindex symbolic links, dereferencing
Do not dereference symbolic links, with one exception:
if a command line argument specifies a symbolic link that refers to
a directory, show information for that directory rather than for the
link itself.
This is the default behavior when no other dereferencing-related
option has been specified (@option{--classify} (@option{-F}),
@option{--directory} (@option{-d}),
(@option{-l}),
@option{--dereference} (@option{-L}), or
@option{--dereference-command-line} (@option{-H})).

@item --group-directories-first
@opindex --group-directories-first
Group all the directories before the files and then sort the
directories and the files separately using the selected sort key
(see --sort option).
That is, this option specifies a primary sort key,
and the --sort option specifies a secondary key.
However, any use of @option{--sort=none}
(@option{-U}) disables this option altogether.

@item --hide=PATTERN
@opindex --hide=@var{pattern}
In directories, ignore files whose names match the shell pattern
@var{pattern}, unless the @option{--all} (@option{-a}) or
@option{--almost-all} (@option{-A}) is also given.  This
option acts like @option{--ignore=@var{pattern}} except that it has no
effect if @option{--all} (@option{-a}) or @option{--almost-all}
(@option{-A}) is also given.

This option can be useful in shell aliases.  For example, if
@command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
lists the file @file{README~} even though @samp{ly -A} would not.

@item -I @var{pattern}
@itemx --ignore=@var{pattern}
@opindex -I
@opindex --ignore=@var{pattern}
In directories, ignore files whose names match the shell pattern
(not regular expression) @var{pattern}.  As
in the shell, an initial @samp{.} in a file name does not match a
wildcard at the start of @var{pattern}.  Sometimes it is useful
to give this option several times.  For example,

@smallexample
$ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
@end smallexample

The first option ignores names of length 3 or more that start with @samp{.},
the second ignores all two-character names that start with @samp{.}
except @samp{..}, and the third ignores names that start with @samp{#}.

@item -L
@itemx --dereference
@opindex -L
@opindex --dereference
@cindex symbolic links, dereferencing
When showing file information for a symbolic link, show information
for the file the link references rather than the link itself.
However, even with this option, @command{ls} still prints the name
of the link itself, not the name of the file that the link points to.

@item -R
@itemx --recursive
@opindex -R
@opindex --recursive
@cindex recursive directory listing
@cindex directory listing, recursive
List the contents of all directories recursively.

@end table


@node What information is listed
@subsection What information is listed

These options affect the information that @command{ls} displays.  By
default, only file names are shown.

@table @samp

@item --author
@opindex --author
@cindex hurd, author, printing
List each file's author when producing long format directory listings.
In GNU/Hurd, file authors can differ from their owners, but in other
operating systems the two are the same.

@item -D
@itemx --dired
@opindex -D
@opindex --dired
@cindex dired Emacs mode support
With the long listing (@option{-l}) format, print an additional line after
the main output:

@example
//DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
@end example

@noindent
The @var{begn} and @var{endn} are unsigned integers that record the
byte position of the beginning and end of each file name in the output.
This makes it easy for Emacs to find the names, even when they contain
unusual characters such as space or newline, without fancy searching.

If directories are being listed recursively (@option{-R}), output a similar
line with offsets for each subdirectory name:

@example
//SUBDIRED// @var{beg1} @var{end1} @dots{}
@end example

Finally, output a line of the form:

@example
//DIRED-OPTIONS// --quoting-style=@var{word}
@end example

@noindent
where @var{word} is the quoting style (@pxref{Formatting the file names}).

Here is an actual example:

@example
$ mkdir -p a/sub/deeper a/sub2
$ touch a/f1 a/f2
$ touch a/sub/deeper/file
$ ls -gloRF --dired a
  a:
  total 8
  -rw-r--r-- 1    0 Jun 10 12:27 f1
  -rw-r--r-- 1    0 Jun 10 12:27 f2
  drwxr-xr-x 3 4096 Jun 10 12:27 sub/
  drwxr-xr-x 2 4096 Jun 10 12:27 sub2/

  a/sub:
  total 4
  drwxr-xr-x 2 4096 Jun 10 12:27 deeper/

  a/sub/deeper:
  total 0
  -rw-r--r-- 1 0 Jun 10 12:27 file

  a/sub2:
  total 0
//DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
//SUBDIRED// 2 3 167 172 228 240 290 296
//DIRED-OPTIONS// --quoting-style=literal
@end example

Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
@file{file}.
The offsets on the @samp{//SUBDIRED//} line delimit the following
directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.

Here is an example of how to extract the fifth entry name, @samp{deeper},
corresponding to the pair of offsets, 222 and 228:

@example
$ ls -gloRF --dired a > out
$ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
deeper
@end example

Note that although the listing above includes a trailing slash
for the @samp{deeper} entry, the offsets select the name without
the trailing slash.  However, if you invoke @command{ls} with @option{--dired}
along with an option like @option{--escape} (aka @option{-b}) and operate
on a file whose name contains special characters, notice that the backslash
@emph{is} included:

@example
$ touch 'a b'
$ ls -blog --dired 'a b'
  -rw-r--r-- 1 0 Jun 10 12:28 a\ b
//DIRED// 30 34
//DIRED-OPTIONS// --quoting-style=escape
@end example

If you use a quoting style that adds quote marks
(e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
So beware that the user may select the quoting style via the environment
variable @env{QUOTING_STYLE}@.  Hence, applications using @option{--dired}
should either specify an explicit @option{--quoting-style=literal} option
(aka @option{-N} or @option{--literal}) on the command line, or else be
prepared to parse the escaped names.

@item --full-time
@opindex --full-time
Produce long format directory listings, and list times in full.  It is
equivalent to using @option{--format=long} with
@option{--time-style=full-iso} (@pxref{Formatting file timestamps}).

@item -g
@opindex -g
Produce long format directory listings, but don't display owner information.

@item -G
@itemx --no-group
@opindex -G
@opindex --no-group
Inhibit display of group information in a long format directory listing.
(This is the default in some non-GNU versions of @command{ls}, so we
provide this option for compatibility.)

@optHumanReadable

@item -i
@itemx --inode
@opindex -i
@opindex --inode
@cindex inode number, printing
Print the inode number (also called the file serial number and index
number) of each file to the left of the file name.  (This number
uniquely identifies each file within a particular file system.)

@item -l
@itemx --format=long
@itemx --format=verbose
@opindex -l
@opindex --format
@opindex long ls @r{format}
@opindex verbose ls @r{format}
In addition to the name of each file, print the file type, file mode bits,
number of hard links, owner name, group name, size, and
timestamp (@pxref{Formatting file timestamps}), normally
the modification time.  Print question marks for information that
cannot be determined.

Normally the size is printed as a byte count without punctuation, but
this can be overridden (@pxref{Block size}).  For example, @option{-h}
prints an abbreviated, human-readable count, and
@samp{--block-size="'1"} prints a byte count with the thousands
separator of the current locale.

For each directory that is listed, preface the files with a line
@samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
for all files in that directory.  The block size currently defaults to 1024
bytes, but this can be overridden (@pxref{Block size}).
The @var{blocks} computed counts each hard link separately;
this is arguably a deficiency.

The file type is one of the following characters:

@c The commented-out entries are ones we're not sure about.

@table @samp
@item -
regular file
@item b
block special file
@item c
character special file
@item C
high performance (``contiguous data'') file
@item d
directory
@item D
door (Solaris 2.5 and up)
@c @item F
@c semaphore, if this is a distinct file type
@item l
symbolic link
@c @item m
@c multiplexed file (7th edition Unix; obsolete)
@item M
off-line (``migrated'') file (Cray DMF)
@item n
network special file (HP-UX)
@item p
FIFO (named pipe)
@item P
port (Solaris 10 and up)
@c @item Q
@c message queue, if this is a distinct file type
@item s
socket
@c @item S
@c shared memory object, if this is a distinct file type
@c @item T
@c typed memory object, if this is a distinct file type
@c @item w
@c whiteout (4.4BSD; not implemented)
@item ?
some other file type
@end table

@cindex permissions, output by @command{ls}
The file mode bits listed are similar to symbolic mode specifications
(@pxref{Symbolic Modes}).  But @command{ls} combines multiple bits into the
third character of each set of permissions as follows:

@table @samp
@item s
If the set-user-ID or set-group-ID bit and the corresponding executable bit
are both set.

@item S
If the set-user-ID or set-group-ID bit is set but the corresponding
executable bit is not set.

@item t
If the restricted deletion flag or sticky bit, and the
other-executable bit, are both set.  The restricted deletion flag is
another name for the sticky bit.  @xref{Mode Structure}.

@item T
If the restricted deletion flag or sticky bit is set but the
other-executable bit is not set.

@item x
If the executable bit is set and none of the above apply.

@item -
Otherwise.
@end table

Following the file mode bits is a single character that specifies
whether an alternate access method such as an access control list
applies to the file.  When the character following the file mode bits is a
space, there is no alternate access method.  When it is a printing
character, then there is such a method.

GNU @command{ls} uses a @samp{.} character to indicate a file
with a security context, but no other alternate access method.

A file with any other combination of alternate access methods
is marked with a @samp{+} character.

@item -n
@itemx --numeric-uid-gid
@opindex -n
@opindex --numeric-uid-gid
@cindex numeric uid and gid
@cindex numeric user and group IDs
Produce long format directory listings, but
display numeric user and group IDs instead of the owner and group names.

@item -o
@opindex -o
Produce long format directory listings, but don't display group information.
It is equivalent to using @option{--format=long} with @option{--no-group} .

@item -s
@itemx --size
@opindex -s
@opindex --size
@cindex disk allocation
@cindex size of files, reporting
Print the disk allocation of each file to the left of the file name.
This is the amount of disk space used by the file, which is usually a
bit more than the file's size, but it can be less if the file has holes.

Normally the disk allocation is printed in units of
1024 bytes, but this can be overridden (@pxref{Block size}).

@cindex NFS mounts from BSD to HP-UX
For files that are NFS-mounted from an HP-UX system to a BSD system,
this option reports sizes that are half the correct values.  On HP-UX
systems, it reports sizes that are twice the correct values for files
that are NFS-mounted from BSD systems.  This is due to a flaw in HP-UX;
it also affects the HP-UX @command{ls} program.

@optSi

@item -Z
@itemx --context
@opindex -Z
@opindex --context
@cindex SELinux
@cindex security context
Display the SELinux security context or @samp{?} if none is found.
When used with the @option{-l} option, print the security context
to the left of the size column.

@end table


@node Sorting the output
@subsection Sorting the output

@cindex sorting @command{ls} output
These options change the order in which @command{ls} sorts the information
it outputs.  By default, sorting is done by character code
(e.g., ASCII order).

@table @samp

@item -c
@itemx --time=ctime
@itemx --time=status
@opindex -c
@opindex --time
@opindex ctime@r{, printing or sorting by}
@opindex status time@r{, printing or sorting by}
@opindex use time@r{, printing or sorting files by}
If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
print the status change time (the @samp{ctime} in the inode) instead of
the modification time.
When explicitly sorting by time (@option{--sort=time} or @option{-t})
or when not using a long listing format,
sort according to the status change time.

@item -f
@opindex -f
@cindex unsorted directory listing
@cindex directory order, listing by
Primarily, like @option{-U}---do not sort; list the files in whatever
order they are stored in the directory.  But also enable @option{-a} (list
all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
were specified before the @option{-f}).

@item -r
@itemx --reverse
@opindex -r
@opindex --reverse
@cindex reverse sorting
Reverse whatever the sorting method is---e.g., list files in reverse
alphabetical order, youngest first, smallest first, or whatever.

@item -S
@itemx --sort=size
@opindex -S
@opindex --sort
@opindex size of files@r{, sorting files by}
Sort by file size, largest first.

@item -t
@itemx --sort=time
@opindex -t
@opindex --sort
@opindex modification time@r{, sorting files by}
Sort by modification time (the @samp{mtime} in the inode), newest first.

@item -u
@itemx --time=atime
@itemx --time=access
@itemx --time=use
@opindex -u
@opindex --time
@opindex use time@r{, printing or sorting files by}
@opindex atime@r{, printing or sorting files by}
@opindex access time@r{, printing or sorting files by}
If the long listing format (e.g., @option{--format=long}) is being used,
print the last access time (the @samp{atime} in the inode).
When explicitly sorting by time (@option{--sort=time} or @option{-t})
or when not using a long listing format, sort according to the access time.

@item -U
@itemx --sort=none
@opindex -U
@opindex --sort
@opindex none@r{, sorting option for @command{ls}}
Do not sort; list the files in whatever order they are
stored in the directory.  (Do not do any of the other unrelated things
that @option{-f} does.)  This is especially useful when listing very large
directories, since not doing any sorting can be noticeably faster.

@item -v
@itemx --sort=version
@opindex -v
@opindex --sort
@opindex version@r{, sorting option for @command{ls}}
Sort by version name and number, lowest first.  It behaves like a default
sort, except that each sequence of decimal digits is treated numerically
as an index/version number.  (@xref{Details about version sort}.)

@item -X
@itemx --sort=extension
@opindex -X
@opindex --sort
@opindex extension@r{, sorting files by}
Sort directory contents alphabetically by file extension (characters
after the last @samp{.}); files with no extension are sorted first.

@end table


@node Details about version sort
@subsection Details about version sort

Version sorting handles the fact that file names frequently include indices or
version numbers.  Standard sorting usually does not produce the order that one
expects because comparisons are made on a character-by-character basis.
Version sorting is especially useful when browsing directories that contain
many files with indices/version numbers in their names:

@example
$ ls -1            $ ls -1v
abc.zml-1.gz       abc.zml-1.gz
abc.zml-12.gz      abc.zml-2.gz
abc.zml-2.gz       abc.zml-12.gz
@end example

Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
@var{ver1} < @var{ver2} implies that the name composed of
``@var{prefix} @var{ver1} @var{suffix}'' sorts before
``@var{prefix} @var{ver2} @var{suffix}''.

Note also that leading zeros of numeric parts are ignored:

@example
$ ls -1            $ ls -1v
abc-1.007.tgz      abc-1.01a.tgz
abc-1.012b.tgz     abc-1.007.tgz
abc-1.01a.tgz      abc-1.012b.tgz
@end example

This functionality is implemented using gnulib's @code{filevercmp} function,
which has some caveats worth noting.

@itemize @bullet
@item @env{LC_COLLATE} is ignored, which means @samp{ls -v} and @samp{sort -V}
will sort non-numeric prefixes as if the @env{LC_COLLATE} locale category
was set to @samp{C}@.
@item Some suffixes will not be matched by the regular
expression mentioned above.  Consequently these examples may
not sort as you expect:

@example
abc-1.2.3.4.7z
abc-1.2.3.7z
@end example

@example
abc-1.2.3.4.x86_64.rpm
abc-1.2.3.x86_64.rpm
@end example
@end itemize

@node General output formatting
@subsection General output formatting

These options affect the appearance of the overall output.

@table @samp

@item -1
@itemx --format=single-column
@opindex -1
@opindex --format
@opindex single-column @r{output of files}
List one file per line.  This is the default for @command{ls} when standard
output is not a terminal.  See also the @option{-b} and @option{-q} options
to suppress direct output of newline characters within a file name.

@item -C
@itemx --format=vertical
@opindex -C
@opindex --format
@opindex vertical @r{sorted files in columns}
List files in columns, sorted vertically.  This is the default for
@command{ls} if standard output is a terminal.  It is always the default
for the @command{dir} program.
GNU @command{ls} uses variable width columns to display as many files as
possible in the fewest lines.

@item --color [=@var{when}]
@opindex --color
@cindex color, distinguishing file types with
Specify whether to use color for distinguishing file types.  @var{when}
may be omitted, or one of:
@itemize @bullet
@item none
@vindex none @r{color option}
- Do not use color at all.  This is the default.
@item auto
@vindex auto @r{color option}
@cindex terminal, using color iff
- Only use color if standard output is a terminal.
@item always
@vindex always @r{color option}
- Always use color.
@end itemize
Specifying @option{--color} and no @var{when} is equivalent to
@option{--color=always}.
Piping a colorized listing through a pager like @command{more} or
@command{less} usually produces unreadable results.  However, using
@code{more -f} does seem to work.

@vindex LS_COLORS
@vindex SHELL @r{environment variable, and color}
Note that using the @option{--color} option may incur a noticeable
performance penalty when run in a directory with very many entries,
because the default settings require that @command{ls} @code{stat} every
single file it lists.
However, if you would like most of the file-type coloring
but can live without the other coloring options (e.g.,
executable, orphan, sticky, other-writable, capability), use
@command{dircolors} to set the @env{LS_COLORS} environment variable like this,
@example
eval $(dircolors -p | perl -pe \
  's/^((CAP|S[ET]|O[TR]|M|E)\w+).*/$1 00/' | dircolors -)
@end example
and on a @code{dirent.d_type}-capable file system, @command{ls}
will perform only one @code{stat} call per command line argument.

@item -F
@itemx --classify
@itemx --indicator-style=classify
@opindex -F
@opindex --classify
@opindex --indicator-style
@cindex file type and executables, marking
@cindex executables and file type, marking
Append a character to each file name indicating the file type.  Also,
for regular files that are executable, append @samp{*}.  The file type
indicators are @samp{/} for directories, @samp{@@} for symbolic links,
@samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
and nothing for regular files.
@c The following sentence is the same as the one for -d.
Do not follow symbolic links listed on the
command line unless the @option{--dereference-command-line} (@option{-H}),
@option{--dereference} (@option{-L}), or
@option{--dereference-command-line-symlink-to-dir} options are specified.

@item --file-type
@itemx --indicator-style=file-type
@opindex --file-type
@opindex --indicator-style
@cindex file type, marking
Append a character to each file name indicating the file type.  This is
like @option{-F}, except that executables are not marked.

@item --indicator-style=@var{word}
@opindex --indicator-style
Append a character indicator with style @var{word} to entry names,
as follows:

@table @samp
@item none
Do not append any character indicator; this is the default.
@item slash
Append @samp{/} for directories.  This is the same as the @option{-p}
option.
@item file-type
Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
for FIFOs, @samp{=} for sockets, and nothing for regular files.  This is
the same as the @option{--file-type} option.
@item classify
Append @samp{*} for executable regular files, otherwise behave as for
@samp{file-type}.  This is the same as the @option{-F} or
@option{--classify} option.
@end table

@item -k
@itemx --kibibytes
@opindex -k
@opindex --kibibytes
Set the default block size to its normal value of 1024 bytes,
overriding any contrary specification in environment variables
(@pxref{Block size}).  This option is in turn overridden by the
@option{--block-size}, @option{-h} or @option{--human-readable}, and
@option{--si} options.

The @option{-k} or @option{--kibibytes} option affects the
per-directory block count written by the @option{-l} and similar
options, and the size written by the @option{-s} or @option{--size}
option.  It does not affect the file size written by @option{-l}.

@item -m
@itemx --format=commas
@opindex -m
@opindex --format
@opindex commas@r{, outputting between files}
List files horizontally, with as many as will fit on each line,
separated by @samp{, } (a comma and a space).

@item -p
@itemx --indicator-style=slash
@opindex -p
@opindex --indicator-style
@cindex file type, marking
Append a @samp{/} to directory names.

@item -x
@itemx --format=across
@itemx --format=horizontal
@opindex -x
@opindex --format
@opindex across@r{, listing files}
@opindex horizontal@r{, listing files}
List the files in columns, sorted horizontally.

@item -T @var{cols}
@itemx --tabsize=@var{cols}
@opindex -T
@opindex --tabsize
Assume that each tab stop is @var{cols} columns wide.  The default is 8.
@command{ls} uses tabs where possible in the output, for efficiency.  If
@var{cols} is zero, do not use tabs at all.

Some terminal emulators might not properly align columns to the right of a
TAB following a non-ASCII byte.  You can avoid that issue by using the
@option{-T0} option or put @code{TABSIZE=0} in your environment, to tell
@command{ls} to align using spaces, not tabs.

@item -w @var{cols}
@itemx --width=@var{cols}
@opindex -w
@opindex --width
@vindex COLUMNS
Assume the screen is @var{cols} columns wide.  The default is taken
from the terminal settings if possible; otherwise the environment
variable @env{COLUMNS} is used if it is set; otherwise the default
is 80.  With a @var{cols} value of @samp{0}, there is no limit on
the length of the output line, and that single output line will
be delimited with spaces, not tabs.

@end table


@node Formatting file timestamps
@subsection Formatting file timestamps

By default, file timestamps are listed in abbreviated form, using
a date like @samp{Mar 30@ @ 2002} for non-recent timestamps, and a
date-without-year and time like @samp{Mar 30 23:45} for recent timestamps.
This format can change depending on the current locale as detailed below.

@cindex clock skew
A timestamp is considered to be @dfn{recent} if it is less than six
months old, and is not dated in the future.  If a timestamp dated
today is not listed in recent form, the timestamp is in the future,
which means you probably have clock skew problems which may break
programs like @command{make} that rely on file timestamps.

@vindex TZ
Time stamps are listed according to the time zone rules specified by
the @env{TZ} environment variable, or by the system default rules if
@env{TZ} is not set.  @xref{TZ Variable,, Specifying the Time Zone
with @env{TZ}, libc, The GNU C Library Reference Manual}.

The following option changes how file timestamps are printed.

@table @samp
@item --time-style=@var{style}
@opindex --time-style
@cindex time style
List timestamps in style @var{style}.  The @var{style} should
be one of the following:

@table @samp
@item +@var{format}
@vindex LC_TIME
List timestamps using @var{format}, where @var{format} is interpreted
like the format argument of @command{date} (@pxref{date invocation}).
For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
@command{ls} to list timestamps like @samp{2002-03-30 23:45:56}.  As
with @command{date}, @var{format}'s interpretation is affected by the
@env{LC_TIME} locale category.

If @var{format} contains two format strings separated by a newline,
the former is used for non-recent files and the latter for recent
files; if you want output columns to line up, you may need to insert
spaces in one of the two formats.

@item full-iso
List timestamps in full using ISO 8601 date, time, and time zone
components with nanosecond precision, e.g., @samp{2002-03-30
23:45:56.477817180 -0700}.  This style is equivalent to
@samp{+%Y-%m-%d %H:%M:%S.%N %z}.

This is useful because the time output includes all the information that
is available from the operating system.  For example, this can help
explain @command{make}'s behavior, since GNU @command{make}
uses the full timestamp to determine whether a file is out of date.

@item long-iso
List ISO 8601 date and time components with minute precision, e.g.,
@samp{2002-03-30 23:45}.  These timestamps are shorter than
@samp{full-iso} timestamps, and are usually good enough for everyday
work.  This style is equivalent to @samp{+%Y-%m-%d %H:%M}.

@item iso
List ISO 8601 dates for non-recent timestamps (e.g.,
@samp{2002-03-30@ }), and ISO 8601-like month, day, hour, and
minute for recent timestamps (e.g., @samp{03-30 23:45}).  These
timestamps are uglier than @samp{long-iso} timestamps, but they carry
nearly the same information in a smaller space and their brevity helps
@command{ls} output fit within traditional 80-column output lines.
The following two @command{ls} invocations are equivalent:

@example
newline='
'
ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
ls -l --time-style="iso"
@end example

@item locale
@vindex LC_TIME
List timestamps in a locale-dependent form.  For example, a Finnish
locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
and recent timestamps like @samp{maalis 30 23:45}.  Locale-dependent
timestamps typically consume more space than @samp{iso} timestamps and
are harder for programs to parse because locale conventions vary so
widely, but they are easier for many people to read.

The @env{LC_TIME} locale category specifies the timestamp format.  The
default POSIX locale uses timestamps like @samp{Mar 30@
@ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
@command{ls} invocations are equivalent:

@example
newline='
'
ls -l --time-style="+%b %e  %Y$newline%b %e %H:%M"
ls -l --time-style="locale"
@end example

Other locales behave differently.  For example, in a German locale,
@option{--time-style="locale"} might be equivalent to
@option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
and might generate timestamps like @samp{30. M@"ar 2002@ } and
@samp{30. M@"ar 23:45}.

@item posix-@var{style}
@vindex LC_TIME
List POSIX-locale timestamps if the @env{LC_TIME} locale
category is POSIX, @var{style} timestamps otherwise.  For
example, the @samp{posix-long-iso} style lists
timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
the POSIX locale, and like @samp{2002-03-30 23:45} otherwise.
@end table
@end table

@vindex TIME_STYLE
You can specify the default value of the @option{--time-style} option
with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
the default style is @samp{locale}.  GNU Emacs 21.3 and
later use the @option{--dired} option and therefore can parse any date
format, but if you are using Emacs 21.1 or 21.2 and specify a
non-POSIX locale you may need to set
@samp{TIME_STYLE="posix-long-iso"}.

To avoid certain denial-of-service attacks, timestamps that would be
longer than 1000 bytes may be treated as errors.


@node Formatting the file names
@subsection Formatting the file names

These options change how file names themselves are printed.

@table @samp

@item -b
@itemx --escape
@itemx --quoting-style=escape
@opindex -b
@opindex --escape
@opindex --quoting-style
@cindex backslash sequences for file names
Quote nongraphic characters in file names using alphabetic and octal
backslash sequences like those used in C.

@item -N
@itemx --literal
@itemx --quoting-style=literal
@opindex -N
@opindex --literal
@opindex --quoting-style
Do not quote file names.  However, with @command{ls} nongraphic
characters are still printed as question marks if the output is a
terminal and you do not specify the @option{--show-control-chars}
option.

@item -q
@itemx --hide-control-chars
@opindex -q
@opindex --hide-control-chars
Print question marks instead of nongraphic characters in file names.
This is the default if the output is a terminal and the program is
@command{ls}.

@item -Q
@itemx --quote-name
@itemx --quoting-style=c
@opindex -Q
@opindex --quote-name
@opindex --quoting-style
Enclose file names in double quotes and quote nongraphic characters as
in C.

@item --quoting-style=@var{word}
@opindex --quoting-style
@cindex quoting style
Use style @var{word} to quote file names and other strings that may
contain arbitrary characters.  The @var{word} should
be one of the following:

@table @samp
@item literal
Output strings as-is; this is the same as the @option{-N} or
@option{--literal} option.
@item shell
Quote strings for the shell if they contain shell metacharacters or would
cause ambiguous output.
The quoting is suitable for POSIX-compatible shells like
@command{bash}, but it does not always work for incompatible shells
like @command{csh}.
@item shell-always
Quote strings for the shell, even if they would normally not require quoting.
@item shell-escape
Like @samp{shell}, but also quoting non-printable characters using the POSIX
proposed @samp{$''} syntax suitable for most shells.
@item shell-escape-always
Like @samp{shell-escape}, but quote strings even if they would
normally not require quoting.
@item c
Quote strings as for C character string literals, including the
surrounding double-quote characters; this is the same as the
@option{-Q} or @option{--quote-name} option.
@item escape
Quote strings as for C character string literals, except omit the
surrounding double-quote
characters; this is the same as the @option{-b} or @option{--escape} option.
@item clocale
Quote strings as for C character string literals, except use
surrounding quotation marks appropriate for the
locale.
@item locale
@c Use @t instead of @samp to avoid duplicate quoting in some output styles.
Quote strings as for C character string literals, except use
surrounding quotation marks appropriate for the locale, and quote
@t{'like this'} instead of @t{"like
this"} in the default C locale.  This looks nicer on many displays.
@end table

You can specify the default value of the @option{--quoting-style} option
with the environment variable @env{QUOTING_STYLE}@.  If that environment
variable is not set, the default value is @samp{shell-escape} when the
output is a terminal, and @samp{literal} otherwise.

@item --show-control-chars
@opindex --show-control-chars
Print nongraphic characters as-is in file names.
This is the default unless the output is a terminal and the program is
@command{ls}.

@end table


@node dir invocation
@section @command{dir}: Briefly list directory contents

@pindex dir
@cindex directory listing, brief

@command{dir} is equivalent to @code{ls -C
-b}; that is, by default files are listed in columns, sorted vertically,
and special characters are represented by backslash escape sequences.

@xref{ls invocation, @command{ls}}.


@node vdir invocation
@section @command{vdir}: Verbosely list directory contents

@pindex vdir
@cindex directory listing, verbose

@command{vdir} is equivalent to @code{ls -l
-b}; that is, by default files are listed in long format and special
characters are represented by backslash escape sequences.

@xref{ls invocation, @command{ls}}.

@node dircolors invocation
@section @command{dircolors}: Color setup for @command{ls}

@pindex dircolors
@cindex color setup
@cindex setup for color

@command{dircolors} outputs a sequence of shell commands to set up the
terminal for color output from @command{ls} (and @command{dir}, etc.).
Typical usage:

@example
eval "$(dircolors [@var{option}]@dots{} [@var{file}])"
@end example

If @var{file} is specified, @command{dircolors} reads it to determine which
colors to use for which file types and extensions.  Otherwise, a
precompiled database is used.  For details on the format of these files,
run @samp{dircolors --print-database}.

To make @command{dircolors} read a @file{~/.dircolors} file if it
exists, you can put the following lines in your @file{~/.bashrc} (or
adapt them to your favorite shell):

@example
d=.dircolors
test -r $d && eval "$(dircolors $d)"
@end example

@vindex LS_COLORS
@vindex SHELL @r{environment variable, and color}
The output is a shell command to set the @env{LS_COLORS} environment
variable.  You can specify the shell syntax to use on the command line,
or @command{dircolors} will guess it from the value of the @env{SHELL}
environment variable.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp
@item -b
@itemx --sh
@itemx --bourne-shell
@opindex -b
@opindex --sh
@opindex --bourne-shell
@cindex Bourne shell syntax for color setup
@cindex @command{sh} syntax for color setup
Output Bourne shell commands.  This is the default if the @env{SHELL}
environment variable is set and does not end with @samp{csh} or
@samp{tcsh}.

@item -c
@itemx --csh
@itemx --c-shell
@opindex -c
@opindex --csh
@opindex --c-shell
@cindex C shell syntax for color setup
@cindex @command{csh} syntax for color setup
Output C shell commands.  This is the default if @code{SHELL} ends with
@command{csh} or @command{tcsh}.

@item -p
@itemx --print-database
@opindex -p
@opindex --print-database
@cindex color database, printing
@cindex database for color setup, printing
@cindex printing color database
Print the (compiled-in) default color configuration database.  This
output is itself a valid configuration file, and is fairly descriptive
of the possibilities.

@end table

@exitstatus


@node Basic operations
@chapter Basic operations

@cindex manipulating files

This chapter describes the commands for basic file manipulation:
copying, moving (renaming), and deleting (removing).

@menu
* cp invocation::               Copy files.
* dd invocation::               Convert and copy a file.
* install invocation::          Copy files and set attributes.
* mv invocation::               Move (rename) files.
* rm invocation::               Remove files or directories.
* shred invocation::            Remove files more securely.
@end menu


@node cp invocation
@section @command{cp}: Copy files and directories

@pindex cp
@cindex copying files and directories
@cindex files, copying
@cindex directories, copying

@command{cp} copies files (or, optionally, directories).  The copy is
completely independent of the original.  You can either copy one file to
another, or copy arbitrarily many files to a destination directory.
Synopses:

@example
cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
@end example

@itemize @bullet
@item
If two file names are given, @command{cp} copies the first file to the
second.

@item
If the @option{--target-directory} (@option{-t}) option is given, or
failing that if the last file is a directory and the
@option{--no-target-directory} (@option{-T}) option is not given,
@command{cp} copies each @var{source} file to the specified directory,
using the @var{source}s' names.
@end itemize

Generally, files are written just as they are read.  For exceptions,
see the @option{--sparse} option below.

By default, @command{cp} does not copy directories.  However, the
@option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
copy recursively by descending into source directories and copying files
to corresponding destination directories.

When copying from a symbolic link, @command{cp} normally follows the
link only when not copying recursively or when @option{--link}
(@option{-l}) is used.  This default can be overridden with the
@option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
(@option{-L}), @option{--no-dereference} (@option{-P}), and
@option{-H} options.  If more than one of these options is specified,
the last one silently overrides the others.

When copying to a symbolic link, @command{cp} follows the
link only when it refers to an existing regular file.
However, when copying to a dangling symbolic link, @command{cp}
refuses by default, and fails with a diagnostic, since the operation
is inherently dangerous.  This behavior is contrary to historical
practice and to POSIX@.
Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
the target of a dangling destination symlink, in spite of the possible risk.
Also, when an option like
@option{--backup} or @option{--link} acts to rename or remove the
destination before copying, @command{cp} renames or removes the
symbolic link rather than the file it points to.

By default, @command{cp} copies the contents of special files only
when not copying recursively.  This default can be overridden with the
@option{--copy-contents} option.

@cindex self-backups
@cindex backups, making only
@command{cp} generally refuses to copy a file onto itself, with the
following exception: if @option{--force --backup} is specified with
@var{source} and @var{dest} identical, and referring to a regular file,
@command{cp} will make a backup file, either regular or numbered, as
specified in the usual ways (@pxref{Backup options}).  This is useful when
you simply want to make a backup of an existing file before changing it.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp
@item -a
@itemx --archive
@opindex -a
@opindex --archive
Preserve as much as possible of the structure and attributes of the
original files in the copy (but do not attempt to preserve internal
directory structure; i.e., @samp{ls -U} may list the entries in a copied
directory in a different order).
Try to preserve SELinux security context and extended attributes (xattr),
but ignore any failure to do that and print no corresponding diagnostic.
Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.

@item --attributes-only
@opindex --attributes-only
Copy only the specified attributes of the source file to the destination.
If the destination already exists, do not alter its contents.
See the @option{--preserve} option for controlling which attributes to copy.

@item -b
@itemx --backup[=@var{method}]
@opindex -b
@opindex --backup
@vindex VERSION_CONTROL
@cindex backups, making
@xref{Backup options}.
Make a backup of each file that would otherwise be overwritten or removed.
As a special case, @command{cp} makes a backup of @var{source} when the force
and backup options are given and @var{source} and @var{dest} are the same
name for an existing, regular file.  One useful application of this
combination of options is this tiny Bourne shell script:

@example
#!/bin/sh
# Usage: backup FILE...
# Create a GNU-style backup of each listed FILE.
fail=0
for i; do
  cp --backup --force --preserve=all -- "$i" "$i" || fail=1
done
exit $fail
@end example

@item --copy-contents
@cindex directories, copying recursively
@cindex copying directories recursively
@cindex recursively copying directories
@cindex non-directories, copying as special files
If copying recursively, copy the contents of any special files (e.g.,
FIFOs and device files) as if they were regular files.  This means
trying to read the data in each source file and writing it to the
destination.  It is usually a mistake to use this option, as it
normally has undesirable effects on special files like FIFOs and the
ones typically found in the @file{/dev} directory.  In most cases,
@code{cp -R --copy-contents} will hang indefinitely trying to read
from FIFOs and special files like @file{/dev/console}, and it will
fill up your destination disk if you use it to copy @file{/dev/zero}.
This option has no effect unless copying recursively, and it does not
affect the copying of symbolic links.

@item -d
@opindex -d
@cindex symbolic links, copying
@cindex hard links, preserving
Copy symbolic links as symbolic links rather than copying the files that
they point to, and preserve hard links between source files in the copies.
Equivalent to @option{--no-dereference --preserve=links}.

@item -f
@itemx --force
@opindex -f
@opindex --force
When copying without this option and an existing destination file cannot
be opened for writing, the copy fails.  However, with @option{--force},
when a destination file cannot be opened, @command{cp} then removes it and
tries to open it again.  Contrast this behavior with that enabled by
@option{--link} and @option{--symbolic-link}, whereby the destination file
is never opened but rather is removed unconditionally.  Also see the
description of @option{--remove-destination}.

This option is independent of the @option{--interactive} or
@option{-i} option: neither cancels the effect of the other.

This option is ignored when the @option{--no-clobber} or @option{-n} option
is also used.

@item -H
@opindex -H
If a command line argument specifies a symbolic link, then copy the
file it points to rather than the symbolic link itself.  However,
copy (preserving its nature) any symbolic link that is encountered
via recursive traversal.

@item -i
@itemx --interactive
@opindex -i
@opindex --interactive
When copying a file other than a directory, prompt whether to
overwrite an existing destination file.  The @option{-i} option overrides
a previous @option{-n} option.

@item -l
@itemx --link
@opindex -l
@opindex --link
Make hard links instead of copies of non-directories.

@item -L
@itemx --dereference
@opindex -L
@opindex --dereference
Follow symbolic links when copying from them.
With this option, @command{cp} cannot create a symbolic link.
For example, a symlink (to regular file) in the source tree will be copied to
a regular file in the destination tree.

@item -n
@itemx --no-clobber
@opindex -n
@opindex --no-clobber
Do not overwrite an existing file.  The @option{-n} option overrides a previous
@option{-i} option.  This option is mutually exclusive with @option{-b} or
@option{--backup} option.

@item -P
@itemx --no-dereference
@opindex -P
@opindex --no-dereference
@cindex symbolic links, copying
Copy symbolic links as symbolic links rather than copying the files that
they point to.  This option affects only symbolic links in the source;
symbolic links in the destination are always followed if possible.

@item -p
@itemx --preserve[=@var{attribute_list}]
@opindex -p
@opindex --preserve
@cindex file information, preserving, extended attributes, xattr
Preserve the specified attributes of the original files.
If specified, the @var{attribute_list} must be a comma-separated list
of one or more of the following strings:

@table @samp
@item mode
Preserve the file mode bits and access control lists.
@item ownership
Preserve the owner and group.  On most modern systems,
only users with appropriate privileges may change the owner of a file,
and ordinary users
may preserve the group ownership of a file only if they happen to be
a member of the desired group.
@item timestamps
Preserve the times of last access and last modification, when possible.
On older systems, it is not possible to preserve these attributes
when the affected file is a symbolic link.
However, many systems now provide the @code{utimensat} function,
which makes it possible even for symbolic links.
@item links
Preserve in the destination files
any links between corresponding source files.
Note that with @option{-L} or @option{-H}, this option can convert
symbolic links to hard links.  For example,
@example
$ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
74161745 a
74161745 b
@end example
@noindent
Note the inputs: @file{b} is a symlink to regular file @file{a},
yet the files in destination directory, @file{c/}, are hard-linked.
Since @option{-a} implies @option{--no-dereference} it would copy the symlink,
but the later @option{-H} tells @command{cp} to dereference the command line
arguments where it then sees two files with the same inode number.
Then the @option{--preserve=links} option also implied by @option{-a}
will preserve the perceived hard link.

Here is a similar example that exercises @command{cp}'s @option{-L} option:
@smallexample
$ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
74163295 a
74163295 b
@end smallexample

@item context
Preserve SELinux security context of the file, or fail with full diagnostics.
@item xattr
Preserve extended attributes of the file, or fail with full diagnostics.
If @command{cp} is built without xattr support, ignore this option.
If SELinux context, ACLs or Capabilities are implemented using xattrs,
they are preserved implicitly by this option as well, i.e., even without
specifying @option{--preserve=mode} or @option{--preserve=context}.
@item all
Preserve all file attributes.
Equivalent to specifying all of the above, but with the difference
that failure to preserve SELinux security context or extended attributes
does not change @command{cp}'s exit status.  In contrast to @option{-a},
all but @samp{Operation not supported} warnings are output.
@end table

Using @option{--preserve} with no @var{attribute_list} is equivalent
to @option{--preserve=mode,ownership,timestamps}.

In the absence of this option, the permissions of existing destination
files are unchanged.  Each new file is created with the mode of the
corresponding source file minus the set-user-ID, set-group-ID, and
sticky bits as the create mode; the operating system then applies either
the umask or a default ACL, possibly resulting in a more restrictive
file mode.
@xref{File permissions}.

@item --no-preserve=@var{attribute_list}
@cindex file information, preserving
Do not preserve the specified attributes.  The @var{attribute_list}
has the same form as for @option{--preserve}.

@item --parents
@opindex --parents
@cindex parent directories and @command{cp}
Form the name of each destination file by appending to the target
directory a slash and the specified name of the source file.  The last
argument given to @command{cp} must be the name of an existing directory.
For example, the command:

@example
cp --parents a/b/c existing_dir
@end example

@noindent
copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
any missing intermediate directories.

@item -R
@itemx -r
@itemx --recursive
@opindex -R
@opindex -r
@opindex --recursive
@cindex directories, copying recursively
@cindex copying directories recursively
@cindex recursively copying directories
@cindex non-directories, copying as special files
Copy directories recursively.  By default, do not follow symbolic
links in the source unless used together with the @option{--link}
(@option{-l}) option; see the @option{--archive} (@option{-a}), @option{-d},
@option{--dereference} (@option{-L}), @option{--no-dereference}
(@option{-P}), and @option{-H} options.  Special files are copied by
creating a destination file of the same type as the source; see the
@option{--copy-contents} option.  It is not portable to use
@option{-r} to copy symbolic links or special files.  On some
non-GNU systems, @option{-r} implies the equivalent of
@option{-L} and @option{--copy-contents} for historical reasons.
Also, it is not portable to use @option{-R} to copy symbolic links
unless you also specify @option{-P}, as POSIX allows
implementations that dereference symbolic links by default.

@item --reflink[=@var{when}]
@opindex --reflink[=@var{when}]
@cindex COW
@cindex clone
@cindex copy on write
Perform a lightweight, copy-on-write (COW) copy, if supported by the
file system.  Once it has succeeded, beware that the source and destination
files share the same disk data blocks as long as they remain unmodified.
Thus, if a disk I/O error affects data blocks of one of the files,
the other suffers the same fate.

The @var{when} value can be one of the following:

@table @samp
@item always
The default behavior: if the copy-on-write operation is not supported
then report the failure for each file and exit with a failure status.

@item auto
If the copy-on-write operation is not supported then fall back
to the standard copy behavior.
@end table

This option is overridden by the @option{--link}, @option{--symbolic-link}
and @option{--attributes-only} options, thus allowing it to be used
to configure the default data copying behavior for @command{cp}.
For example, with the following alias, @command{cp} will use the
minimum amount of space supported by the file system.

@example
alias cp='cp --reflink=auto --sparse=always'
@end example

@item --remove-destination
@opindex --remove-destination
Remove each existing destination file before attempting to open it
(contrast with @option{-f} above).

@item --sparse=@var{when}
@opindex --sparse=@var{when}
@cindex sparse files, copying
@cindex holes, copying files with
@findex read @r{system call, and holes}
A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
does not occupy any physical disk blocks; the @samp{read} system call
reads these as zeros.  This can both save considerable disk space and
increase speed, since many binary files contain lots of consecutive zero
bytes.  By default, @command{cp} detects holes in input source files via a crude
heuristic and makes the corresponding output file sparse as well.
Only regular files may be sparse.

The @var{when} value can be one of the following:

@table @samp
@item auto
The default behavior: if the input file is sparse, attempt to make
the output file sparse, too.  However, if an output file exists but
refers to a non-regular file, then do not attempt to make it sparse.

@item always
For each sufficiently long sequence of zero bytes in the input file,
attempt to create a corresponding hole in the output file, even if the
input file does not appear to be sparse.
This is useful when the input file resides on a file system
that does not support sparse files
(for example,  @samp{efs} file systems in SGI IRIX 5.3 and earlier),
but the output file is on a type of file system that does support them.
Holes may be created only in regular files, so if the destination file
is of some other type, @command{cp} does not even try to make it sparse.

@item never
Never make the output file sparse.
This is useful in creating a file for use with the @command{mkswap} command,
since such a file must not have any holes.
@end table

@optStripTrailingSlashes

@item -s
@itemx --symbolic-link
@opindex -s
@opindex --symbolic-link
@cindex symbolic links, copying with
Make symbolic links instead of copies of non-directories.  All source
file names must be absolute (starting with @samp{/}) unless the
destination files are in the current directory.  This option merely
results in an error message on systems that do not support symbolic links.

@optBackupSuffix

@optTargetDirectory

@optNoTargetDirectory

@item -u
@itemx --update
@opindex -u
@opindex --update
@cindex newer files, copying only
Do not copy a non-directory that has an existing destination with the
same or newer modification time.  If time stamps are being preserved,
the comparison is to the source time stamp truncated to the
resolutions of the destination file system and of the system calls
used to update time stamps; this avoids duplicate work if several
@samp{cp -pu} commands are executed with the same source and destination.
If @option{--preserve=links} is also specified (like with @samp{cp -au}
for example), that will take precedence.  Consequently, depending on the
order that files are processed from the source, newer files in the destination
may be replaced, to mirror hard links in the source.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Print the name of each file before copying it.

@item -x
@itemx --one-file-system
@opindex -x
@opindex --one-file-system
@cindex file systems, omitting copying to different
Skip subdirectories that are on different file systems from the one that
the copy started on.
However, mount point directories @emph{are} copied.

@macro optContext
@item -Z
@itemx --context[=@var{context}]
@opindex -Z
@opindex --context
@cindex SELinux, setting/restoring security context
@cindex security context
Without a specified @var{context}, adjust the SELinux security context according
to the system default type for destination files, similarly to the
@command{restorecon} command.
The long form of this option with a specific context specified,
will set the context for newly created files only.
With a specified context, if both SELinux and SMACK are disabled, a warning is
issued.
@end macro
@optContext
This option is mutually exclusive with the @option{--preserve=context}
option, and overrides the @option{--preserve=all} and @option{-a} options.

@end table

@exitstatus


@node dd invocation
@section @command{dd}: Convert and copy a file

@pindex dd
@cindex converting while copying a file

@command{dd} copies a file (from standard input to standard output, by
default) with a changeable I/O block size, while optionally performing
conversions on it.  Synopses:

@example
dd [@var{operand}]@dots{}
dd @var{option}
@end example

The only options are @option{--help} and @option{--version}.
@xref{Common options}.  @command{dd} accepts the following operands,
whose syntax was inspired by the DD (data definition) statement of
OS/360 JCL.

@table @samp

@item if=@var{file}
@opindex if
Read from @var{file} instead of standard input.

@item of=@var{file}
@opindex of
Write to @var{file} instead of standard output.  Unless
@samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
bytes (or the size specified with @samp{seek=}).

@item ibs=@var{bytes}
@opindex ibs
@cindex block size of input
@cindex input block size
Set the input block size to @var{bytes}.
This makes @command{dd} read @var{bytes} per block.
The default is 512 bytes.

@item obs=@var{bytes}
@opindex obs
@cindex block size of output
@cindex output block size
Set the output block size to @var{bytes}.
This makes @command{dd} write @var{bytes} per block.
The default is 512 bytes.

@item bs=@var{bytes}
@opindex bs
@cindex block size
Set both input and output block sizes to @var{bytes}.
This makes @command{dd} read and write @var{bytes} per block,
overriding any @samp{ibs} and @samp{obs} settings.
In addition, if no data-transforming @option{conv} option is specified,
input is copied to the output as soon as it's read,
even if it is smaller than the block size.

@item cbs=@var{bytes}
@opindex cbs
@cindex block size of conversion
@cindex conversion block size
@cindex fixed-length records, converting to variable-length
@cindex variable-length records, converting to fixed-length
Set the conversion block size to @var{bytes}.
When converting variable-length records to fixed-length ones
(@option{conv=block}) or the reverse (@option{conv=unblock}),
use @var{bytes} as the fixed record length.

@item skip=@var{n}
@opindex skip
Skip @var{n} @samp{ibs}-byte blocks in the input file before copying.
If @samp{iflag=skip_bytes} is specified, @var{n} is interpreted
as a byte count rather than a block count.

@item seek=@var{n}
@opindex seek
Skip @var{n} @samp{obs}-byte blocks in the output file before copying.
if @samp{oflag=seek_bytes} is specified, @var{n} is interpreted
as a byte count rather than a block count.

@item count=@var{n}
@opindex count
Copy @var{n} @samp{ibs}-byte blocks from the input file, instead
of everything until the end of the file.
if @samp{iflag=count_bytes} is specified, @var{n} is interpreted
as a byte count rather than a block count.
Note if the input may return short reads as could be the case
when reading from a pipe for example, @samp{iflag=fullblock}
will ensure that @samp{count=} corresponds to complete input blocks
rather than the traditional POSIX specified behavior of counting
input read operations.

@item status=@var{level}
@opindex status
Transfer information is normally output to stderr upon
receipt of the @samp{INFO} signal or when @command{dd} exits.
Specifying @var{level} will adjust the amount of information printed,
with the last @var{level} specified taking precedence.

@table @samp

@item none
@opindex none @r{dd status=}
Do not print any informational or warning messages to stderr.
Error messages are output as normal.

@item noxfer
@opindex noxfer @r{dd status=}
Do not print the final transfer rate and volume statistics
that normally make up the last status line.

@item progress
@opindex progress @r{dd status=}
Print the transfer rate and volume statistics on stderr,
when processing each input block.  Statistics are output
on a single line at most once every second, but updates
can be delayed when waiting on I/O.

@end table

@item conv=@var{conversion}[,@var{conversion}]@dots{}
@opindex conv
Convert the file as specified by the @var{conversion} argument(s).
(No spaces around any comma(s).)

Conversions:

@table @samp

@item ascii
@opindex ascii@r{, converting to}
Convert EBCDIC to ASCII,
using the conversion table specified by POSIX@.
This provides a 1:1 translation for all 256 bytes.
This option implies @samp{conv=unblock}; input is converted to
ASCII before trailing spaces are deleted.

@item ebcdic
@opindex ebcdic@r{, converting to}
Convert ASCII to EBCDIC@.
This is the inverse of the @samp{ascii} conversion.
This option implies @samp{conv=block}; trailing spaces are added
before being converted to EBCDIC@.

@item ibm
@opindex alternate ebcdic@r{, converting to}
This acts like @samp{conv=ebcdic}, except it
uses the alternate conversion table specified by POSIX@.
This is not a 1:1 translation, but reflects common historical practice
for @samp{~}, @samp{[}, and @samp{]}.

The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
mutually exclusive.  If you use any of these options, you should also
use the @samp{cbs=} option.

@item block
@opindex block @r{(space-padding)}
For each line in the input, output @samp{cbs} bytes, replacing the
input newline with a space and padding with spaces as necessary.

@item unblock
@opindex unblock
Remove any trailing spaces in each @samp{cbs}-sized input block,
and append a newline.

The @samp{block} and @samp{unblock} conversions are mutually exclusive.

@item lcase
@opindex lcase@r{, converting to}
Change uppercase letters to lowercase.

@item ucase
@opindex ucase@r{, converting to}
Change lowercase letters to uppercase.

The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.

@item sparse
@opindex sparse
Try to seek rather than write NUL output blocks.
On a file system that supports sparse files, this will create
sparse output when extending the output file.
Be careful when using this option in conjunction with
@samp{conv=notrunc} or @samp{oflag=append}.
With @samp{conv=notrunc}, existing data in the output file
corresponding to NUL blocks from the input, will be untouched.
With @samp{oflag=append} the seeks performed will be ineffective.
Similarly, when the output is a device rather than a file,
NUL input blocks are not copied, and therefore this option
is most useful with virtual or pre zeroed devices.

@item swab
@opindex swab @r{(byte-swapping)}
@cindex byte-swapping
Swap every pair of input bytes.  GNU @command{dd}, unlike others, works
when an odd number of bytes are read---the last byte is simply copied
(since there is nothing to swap it with).

@item sync
@opindex sync @r{(padding with ASCII NULs)}
Pad every input block to size of @samp{ibs} with trailing zero bytes.
When used with @samp{block} or @samp{unblock}, pad with spaces instead of
zero bytes.

@end table

The following ``conversions'' are really file flags
and don't affect internal processing:

@table @samp
@item excl
@opindex excl
@cindex creating output file, requiring
Fail if the output file already exists; @command{dd} must create the
output file itself.

@item nocreat
@opindex nocreat
@cindex creating output file, avoiding
Do not create the output file; the output file must already exist.

The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.

@item notrunc
@opindex notrunc
@cindex truncating output file, avoiding
Do not truncate the output file.

@item noerror
@opindex noerror
@cindex read errors, ignoring
Continue after read errors.

@item fdatasync
@opindex fdatasync
@cindex synchronized data writes, before finishing
Synchronize output data just before finishing.  This forces a physical
write of output data.

@item fsync
@opindex fsync
@cindex synchronized data and metadata writes, before finishing
Synchronize output data and metadata just before finishing.  This
forces a physical write of output data and metadata.

@end table

@item iflag=@var{flag}[,@var{flag}]@dots{}
@opindex iflag
Access the input file using the flags specified by the @var{flag}
argument(s).  (No spaces around any comma(s).)

@item oflag=@var{flag}[,@var{flag}]@dots{}
@opindex oflag
Access the output file using the flags specified by the @var{flag}
argument(s).  (No spaces around any comma(s).)

Here are the flags.  Not every flag is supported on every operating
system.

@table @samp

@item append
@opindex append
@cindex appending to the output file
Write in append mode, so that even if some other process is writing to
this file, every @command{dd} write will append to the current
contents of the file.  This flag makes sense only for output.
If you combine this flag with the @samp{of=@var{file}} operand,
you should also specify @samp{conv=notrunc} unless you want the
output file to be truncated before being appended to.

@item cio
@opindex cio
@cindex concurrent I/O
Use concurrent I/O mode for data.  This mode performs direct I/O
and drops the POSIX requirement to serialize all I/O to the same file.
A file cannot be opened in CIO mode and with a standard open at the
same time.

@item direct
@opindex direct
@cindex direct I/O
Use direct I/O for data, avoiding the buffer cache.
Note that the kernel may impose restrictions on read or write buffer sizes.
For example, with an ext4 destination file system and a Linux-based kernel,
using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
output buffer size is not a multiple of 512.

@item directory
@opindex directory
@cindex directory I/O

Fail unless the file is a directory.  Most operating systems do not
allow I/O to a directory, so this flag has limited utility.

@item dsync
@opindex dsync
@cindex synchronized data reads
Use synchronized I/O for data.  For the output file, this forces a
physical write of output data on each write.  For the input file,
this flag can matter when reading from a remote file that has been
written to synchronously by some other process.  Metadata (e.g.,
last-access and last-modified time) is not necessarily synchronized.

@item sync
@opindex sync
@cindex synchronized data and metadata I/O
Use synchronized I/O for both data and metadata.

@item nocache
@opindex nocache
@cindex discarding file cache
Request to discard the system data cache for a file.
When count=0 all cached data for the file is specified,
otherwise the cache is dropped for the processed
portion of the file.  Also when count=0,
failure to discard the cache is diagnosed
and reflected in the exit status.

Note data that is not already persisted to storage will not
be discarded from cache, so note the use of the ``sync'' options
in the examples below, which are used to maximize the
effectiveness of the @samp{nocache} flag.

Here are some usage examples:

@example
# Advise to drop cache for whole file
dd if=ifile iflag=nocache count=0

# Ensure drop cache for the whole file
dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0

# Drop cache for part of file
dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null

# Stream data using just the read-ahead cache.
# See also the @samp{direct} flag.
dd if=ifile of=ofile iflag=nocache oflag=nocache,sync
@end example

@item nonblock
@opindex nonblock
@cindex nonblocking I/O
Use non-blocking I/O.

@item noatime
@opindex noatime
@cindex access time
Do not update the file's access time.
Some older file systems silently ignore this flag, so it is a good
idea to test it on your files before relying on it.

@item noctty
@opindex noctty
@cindex controlling terminal
Do not assign the file to be a controlling terminal for @command{dd}.
This has no effect when the file is not a terminal.
On many hosts (e.g., GNU/Linux hosts), this option has no effect
at all.

@item nofollow
@opindex nofollow
@cindex symbolic links, following
Do not follow symbolic links.

@item nolinks
@opindex nolinks
@cindex hard links
Fail if the file has multiple hard links.

@item binary
@opindex binary
@cindex binary I/O
Use binary I/O@.  This option has an effect only on nonstandard
platforms that distinguish binary from text I/O.

@item text
@opindex text
@cindex text I/O
Use text I/O@.  Like @samp{binary}, this option has no effect on
standard platforms.

@item fullblock
@opindex fullblock
Accumulate full blocks from input.  The @code{read} system call
may return early if a full block is not available.
When that happens, continue calling @code{read} to fill the remainder
of the block.
This flag can be used only with @code{iflag}.
This flag is useful with pipes for example
as they may return short reads. In that case,
this flag is needed to ensure that a @samp{count=} argument is
interpreted as a block count rather than a count of read operations.

@item count_bytes
@opindex count_bytes
Interpret the @samp{count=} operand as a byte count,
rather than a block count, which allows specifying
a length that is not a multiple of the I/O block size.
This flag can be used only with @code{iflag}.

@item skip_bytes
@opindex skip_bytes
Interpret the @samp{skip=} operand as a byte count,
rather than a block count, which allows specifying
an offset that is not a multiple of the I/O block size.
This flag can be used only with @code{iflag}.

@item seek_bytes
@opindex seek_bytes
Interpret the @samp{seek=} operand as a byte count,
rather than a block count, which allows specifying
an offset that is not a multiple of the I/O block size.
This flag can be used only with @code{oflag}.

@end table

These flags are not supported on all systems, and @samp{dd} rejects
attempts to use them when they are not supported.  When reading from
standard input or writing to standard output, the @samp{nofollow} and
@samp{noctty} flags should not be specified, and the other flags
(e.g., @samp{nonblock}) can affect how other processes behave with the
affected file descriptors, even after @command{dd} exits.

@end table

@cindex multipliers after numbers
The numeric-valued strings above (@var{n} and @var{bytes})
can be followed by a multiplier: @samp{b}=512, @samp{c}=1,
@samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).

Any block size you specify via @samp{bs=}, @samp{ibs=}, @samp{obs=}, @samp{cbs=}
should not be too large---values larger than a few megabytes
are generally wasteful or (as in the gigabyte..exabyte case) downright
counterproductive or error-inducing.

To process data that is at an offset or size that is not a
multiple of the I/O@ block size, you can use the @samp{skip_bytes},
@samp{seek_bytes} and @samp{count_bytes} flags.  Alternatively
the traditional method of separate @command{dd} invocations can be used.
For example, the following shell commands copy data
in 512 KiB blocks between a disk and a tape, but do not save
or restore a 4 KiB label at the start of the disk:

@example
disk=/dev/rdsk/c0t1d0s2
tape=/dev/rmt/0

# Copy all but the label from disk to tape.
(dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape

# Copy from tape back to disk, but leave the disk label alone.
(dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
@end example

@cindex ddrescue
@cindex disks, failing
For failing disks, other tools come with a great variety of extra
functionality to ease the saving of as much data as possible before the
disk finally dies, e.g.
@uref{http://www.gnu.org/software/ddrescue/, GNU @command{ddrescue}}.
However, in some cases such a tool is not available or the administrator
feels more comfortable with the handling of @command{dd}.
As a simple rescue method, call @command{dd} as shown in the following
example: the options @samp{conv=noerror,sync} are used to continue
after read errors and to pad out bad reads with NULs, while
@samp{iflag=fullblock} caters for short reads (which traditionally never
occur on disk based devices):

@example
# Rescue data from an (unmounted!) partition of a failing disk.
dd conv=noerror,sync iflag=fullblock </dev/sda1 > /mnt/rescue.img
@end example

Sending an @samp{INFO} signal (or @samp{USR1} signal where that is unavailable)
to a running @command{dd} process makes it print I/O statistics to
standard error and then resume copying.   In the example below,
@command{dd} is run in the background to copy 5GB of data.
The @command{kill} command makes it output intermediate I/O statistics,
and when @command{dd} completes normally or is killed by the
@code{SIGINT} signal, it outputs the final statistics.

@example
# Ignore the signal so we never inadvertently terminate the dd child.
# Note this is not needed when SIGINFO is available.
trap '' USR1

# Run dd with the fullblock iflag to avoid short reads
# which can be triggered by reception of signals.
dd iflag=fullblock if=/dev/zero of=/dev/null count=5000000 bs=1000 & pid=$!

# Output stats every second.
while kill -s USR1 $pid 2>/dev/null; do sleep 1; done
@end example

The above script will output in the following format:

@example
3441325+0 records in
3441325+0 records out
3441325000 bytes (3.4 GB, 3.2 GiB) copied, 1.00036 s, 3.4 GB/s
5000000+0 records in
5000000+0 records out
5000000000 bytes (5.0 GB, 4.7 GiB) copied, 1.44433 s, 3.5 GB/s
@end example

The @samp{status=progress} option periodically updates the last line
of the transfer statistics above.

@vindex POSIXLY_CORRECT
On systems lacking the @samp{INFO} signal @command{dd} responds to the
@samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
environment variable is set.

@exitstatus


@node install invocation
@section @command{install}: Copy files and set attributes

@pindex install
@cindex copying files and setting attributes

@command{install} copies files while setting their file mode bits and, if
possible, their owner and group.  Synopses:

@example
install [@var{option}]@dots{} [-T] @var{source} @var{dest}
install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
install [@var{option}]@dots{} -d @var{directory}@dots{}
@end example

@itemize @bullet
@item
If two file names are given, @command{install} copies the first file to the
second.

@item
If the @option{--target-directory} (@option{-t}) option is given, or
failing that if the last file is a directory and the
@option{--no-target-directory} (@option{-T}) option is not given,
@command{install} copies each @var{source} file to the specified
directory, using the @var{source}s' names.

@item
If the @option{--directory} (@option{-d}) option is given,
@command{install} creates each @var{directory} and any missing parent
directories.  Parent directories are created with mode
@samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
current umask.  @xref{Directory Setuid and Setgid}, for how the
set-user-ID and set-group-ID bits of parent directories are inherited.
@end itemize

@cindex Makefiles, installing programs in
@command{install} is similar to @command{cp}, but allows you to control the
attributes of destination files.  It is typically used in Makefiles to
copy programs into their destination directories.  It refuses to copy
files onto themselves.

@cindex extended attributes, xattr
@command{install} never preserves extended attributes (xattr).

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@optBackup

@item -C
@itemx --compare
@opindex -C
@opindex --compare
Compare each pair of source and destination files, and if the destination has
identical content and any specified owner, group, permissions, and possibly
SELinux context, then do not modify the destination at all.
Note this option is best used in conjunction with @option{--user},
@option{--group} and @option{--mode} options, lest @command{install}
incorrectly determines the default attributes that installed files would have
(as it doesn't consider setgid directories and POSIX default ACLs for example).
This could result in redundant copies or attributes that are not reset to the
correct defaults.

@item -c
@opindex -c
Ignored; for compatibility with old Unix versions of @command{install}.

@item -D
@opindex -D
Create any missing parent directories of @var{dest},
then copy @var{source} to @var{dest}.
Explicitly specifying the @option{--target-directory=@var{dir}} will similarly
ensure the presence of that hierarchy before copying @var{source} arguments.

@item -d
@itemx --directory
@opindex -d
@opindex --directory
@cindex directories, creating with given attributes
@cindex parent directories, creating missing
@cindex leading directories, creating missing
Create any missing parent directories, giving them the default
attributes.  Then create each given directory, setting their owner,
group and mode as given on the command line or to the defaults.

@item -g @var{group}
@itemx --group=@var{group}
@opindex -g
@opindex --group
@cindex group ownership of installed files, setting
Set the group ownership of installed files or directories to
@var{group}.  The default is the process's current group.  @var{group}
may be either a group name or a numeric group ID.

@item -m @var{mode}
@itemx --mode=@var{mode}
@opindex -m
@opindex --mode
@cindex permissions of installed files, setting
Set the file mode bits for the installed file or directory to @var{mode},
which can be either an octal number, or a symbolic mode as in
@command{chmod}, with @samp{a=} (no access allowed to anyone) as the
point of departure (@pxref{File permissions}).
The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
execute for the owner, read and execute for group and other, and with
set-user-ID and set-group-ID disabled.
This default is not quite the same as @samp{755}, since it disables
instead of preserving set-user-ID and set-group-ID on directories.
@xref{Directory Setuid and Setgid}.

@item -o @var{owner}
@itemx --owner=@var{owner}
@opindex -o
@opindex --owner
@cindex ownership of installed files, setting
@cindex appropriate privileges
@vindex root @r{as default owner}
If @command{install} has appropriate privileges (is run as root), set the
ownership of installed files or directories to @var{owner}.  The default
is @code{root}.  @var{owner} may be either a user name or a numeric user
ID.

@item --preserve-context
@opindex --preserve-context
@cindex SELinux
@cindex security context
Preserve the SELinux security context of files and directories.
Failure to preserve the context in all of the files or directories
will result in an exit status of 1.  If SELinux is disabled then
print a warning and ignore the option.

@item -p
@itemx --preserve-timestamps
@opindex -p
@opindex --preserve-timestamps
@cindex timestamps of installed files, preserving
Set the time of last access and the time of last modification of each
installed file to match those of each corresponding original file.
When a file is installed without this option, its last access and
last modification times are both set to the time of installation.
This option is useful if you want to use the last modification times
of installed files to keep track of when they were last built as opposed
to when they were last installed.

@item -s
@itemx --strip
@opindex -s
@opindex --strip
@cindex symbol table information, stripping
@cindex stripping symbol table information
Strip the symbol tables from installed binary executables.

@item --strip-program=@var{program}
@opindex --strip-program
@cindex symbol table information, stripping, program
Program used to strip binaries.

@optBackupSuffix

@optTargetDirectory
Also specifying the @option{-D} option will ensure the directory is present.

@optNoTargetDirectory

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Print the name of each file before copying it.

@optContext
This option is mutually exclusive with the @option{--preserve-context} option.


@end table

@exitstatus


@node mv invocation
@section @command{mv}: Move (rename) files

@pindex mv

@command{mv} moves or renames files (or directories).  Synopses:

@example
mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
@end example

@itemize @bullet
@item
If two file names are given, @command{mv} moves the first file to the
second.

@item
If the @option{--target-directory} (@option{-t}) option is given, or
failing that if the last file is a directory and the
@option{--no-target-directory} (@option{-T}) option is not given,
@command{mv} moves each @var{source} file to the specified
directory, using the @var{source}s' names.
@end itemize

@command{mv} can move any type of file from one file system to another.
Prior to version @code{4.0} of the fileutils,
@command{mv} could move only regular files between file systems.
For example, now @command{mv} can move an entire directory hierarchy
including special device files from one partition to another.  It first
uses some of the same code that's used by @code{cp -a} to copy the
requested directories and files, then (assuming the copy succeeded)
it removes the originals.  If the copy fails, then the part that was
copied to the destination partition is removed.  If you were to copy
three directories from one partition to another and the copy of the first
directory succeeded, but the second didn't, the first would be left on
the destination partition and the second and third would be left on the
original partition.

@cindex extended attributes, xattr
@command{mv} always tries to copy extended attributes (xattr), which may
include SELinux context, ACLs or Capabilities.
Upon failure all but @samp{Operation not supported} warnings are output.

@cindex prompting, and @command{mv}
If a destination file exists but is normally unwritable, standard input
is a terminal, and the @option{-f} or @option{--force} option is not given,
@command{mv} prompts the user for whether to replace the file.  (You might
own the file, or have write permission on its directory.)  If the
response is not affirmative, the file is skipped.

@emph{Warning}: Avoid specifying a source name with a trailing slash,
when it might be a symlink to a directory.
Otherwise, @command{mv} may do something very surprising, since
its behavior depends on the underlying rename system call.
On a system with a modern Linux-based kernel, it fails with
@code{errno=ENOTDIR}@.
However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
renames not the symlink but rather the directory referenced by the symlink.
@xref{Trailing slashes}.

@emph{Note}: @command{mv} will only replace empty directories in the
destination.  Conflicting populated directories are skipped with a diagnostic.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@optBackup

@item -f
@itemx --force
@opindex -f
@opindex --force
@cindex prompts, omitting
Do not prompt the user before removing a destination file.
@macro mvOptsIfn
If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
options, only the final one takes effect.
@end macro
@mvOptsIfn

@item -i
@itemx --interactive
@opindex -i
@opindex --interactive
@cindex prompts, forcing
Prompt whether to overwrite each existing destination file, regardless
of its permissions.
If the response is not affirmative, the file is skipped.
@mvOptsIfn

@item -n
@itemx --no-clobber
@opindex -n
@opindex --no-clobber
@cindex prompts, omitting
Do not overwrite an existing file.
@mvOptsIfn
This option is mutually exclusive with @option{-b} or @option{--backup} option.

@item -u
@itemx --update
@opindex -u
@opindex --update
@cindex newer files, moving only
Do not move a non-directory that has an existing destination with the
same or newer modification time.
If the move is across file system boundaries, the comparison is to the
source time stamp truncated to the resolutions of the destination file
system and of the system calls used to update time stamps; this avoids
duplicate work if several @samp{mv -u} commands are executed with the
same source and destination.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Print the name of each file before moving it.

@optStripTrailingSlashes

@optBackupSuffix

@optTargetDirectory

@optNoTargetDirectory

@item -Z
@itemx --context
@opindex -Z
@opindex --context
@cindex SELinux, restoring security context
@cindex security context
This option functions similarly to the @command{restorecon} command,
by adjusting the SELinux security context according
to the system default type for destination files and each created directory.

@end table

@exitstatus


@node rm invocation
@section @command{rm}: Remove files or directories

@pindex rm
@cindex removing files or directories

@command{rm} removes each given @var{file}.  By default, it does not remove
directories.  Synopsis:

@example
rm [@var{option}]@dots{} [@var{file}]@dots{}
@end example

@cindex prompting, and @command{rm}
If the @option{-I} or @option{--interactive=once} option is given,
and there are more than three files or the @option{-r}, @option{-R},
or @option{--recursive} are given, then @command{rm} prompts the user
for whether to proceed with the entire operation.  If the response is
not affirmative, the entire command is aborted.

Otherwise, if a file is unwritable, standard input is a terminal, and
the @option{-f} or @option{--force} option is not given, or the
@option{-i} or @option{--interactive=always} option @emph{is} given,
@command{rm} prompts the user for whether to remove the file.
If the response is not affirmative, the file is skipped.

Any attempt to remove a file whose last file name component is
@file{.} or @file{..} is rejected without any prompting, as mandated
by POSIX.

@emph{Warning}: If you use @command{rm} to remove a file, it is usually
possible to recover the contents of that file.  If you want more assurance
that the contents are truly unrecoverable, consider using @command{shred}.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -d
@itemx --dir
@opindex -d
@opindex --dir
@cindex directories, removing
Remove the listed directories if they are empty.

@item -f
@itemx --force
@opindex -f
@opindex --force
Ignore nonexistent files and missing operands, and never prompt the user.
Ignore any previous @option{--interactive} (@option{-i}) option.

@item -i
@opindex -i
Prompt whether to remove each file.
If the response is not affirmative, the file is skipped.
Ignore any previous @option{--force} (@option{-f}) option.
Equivalent to @option{--interactive=always}.

@item -I
@opindex -I
Prompt once whether to proceed with the command, if more than three
files are named or if a recursive removal is requested.  Ignore any
previous @option{--force} (@option{-f}) option.  Equivalent to
@option{--interactive=once}.

@item --interactive [=@var{when}]
@opindex --interactive
Specify when to issue an interactive prompt.  @var{when} may be
omitted, or one of:
@itemize @bullet
@item never
@vindex never @r{interactive option}
- Do not prompt at all.
@item once
@vindex once @r{interactive option}
- Prompt once if more than three files are named or if a recursive
removal is requested.  Equivalent to @option{-I}.
@item always
@vindex always @r{interactive option}
- Prompt for every file being removed.  Equivalent to @option{-i}.
@end itemize
@option{--interactive} with no @var{when} is equivalent to
@option{--interactive=always}.

@item --one-file-system
@opindex --one-file-system
@cindex one file system, restricting @command{rm} to
When removing a hierarchy recursively, skip any directory that is on a
file system different from that of the corresponding command line argument.

@cindex bind mount
This option is useful when removing a build ``chroot'' hierarchy,
which normally contains no valuable data.  However, it is not uncommon
to bind-mount @file{/home} into such a hierarchy, to make it easier to
use one's start-up file.  The catch is that it's easy to forget to
unmount @file{/home}.  Then, when you use @command{rm -rf} to remove
your normally throw-away chroot, that command will remove everything
under @file{/home}, too.
Use the @option{--one-file-system} option, and it will
warn about and skip directories on other file systems.
Of course, this will not save your @file{/home} if it and your
chroot happen to be on the same file system.

@item --preserve-root
@opindex --preserve-root
@cindex root directory, disallow recursive destruction
Fail upon any attempt to remove the root directory, @file{/},
when used with the @option{--recursive} option.
This is the default behavior.
@xref{Treating / specially}.

@item --no-preserve-root
@opindex --no-preserve-root
@cindex root directory, allow recursive destruction
Do not treat @file{/} specially when removing recursively.
This option is not recommended unless you really want to
remove all the files on your computer.
@xref{Treating / specially}.

@item -r
@itemx -R
@itemx --recursive
@opindex -r
@opindex -R
@opindex --recursive
@cindex directories, removing (recursively)
Remove the listed directories and their contents recursively.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Print the name of each file before removing it.

@end table

@cindex files beginning with @samp{-}, removing
@cindex @samp{-}, removing files beginning with
One common question is how to remove files whose names begin with a
@samp{-}.  GNU @command{rm}, like every program that uses the @code{getopt}
function to parse its arguments, lets you use the @samp{--} option to
indicate that all following arguments are non-options.  To remove a file
called @file{-f} in the current directory, you could type either:

@example
rm -- -f
@end example

@noindent
or:

@example
rm ./-f
@end example

@opindex - @r{and Unix @command{rm}}
The Unix @command{rm} program's use of a single @samp{-} for this purpose
predates the development of the @code{getopt} standard syntax.

@exitstatus


@node shred invocation
@section @command{shred}: Remove files more securely

@pindex shred
@cindex data, erasing
@cindex erasing data

@command{shred} overwrites devices or files, to help prevent even
very expensive hardware from recovering the data.

Ordinarily when you remove a file (@pxref{rm invocation}), the data is
not actually destroyed.  Only the index listing where the file is
stored is destroyed, and the storage is made available for reuse.
There are undelete utilities that will attempt to reconstruct the index
and can bring the file back if the parts were not reused.

On a busy system with a nearly-full drive, space can get reused in a few
seconds.  But there is no way to know for sure.  If you have sensitive
data, you may want to be sure that recovery is not possible by actually
overwriting the file with non-sensitive data.

However, even after doing that, it is possible to take the disk back
to a laboratory and use a lot of sensitive (and expensive) equipment
to look for the faint ``echoes'' of the original data underneath the
overwritten data.  If the data has only been overwritten once, it's not
even that hard.

The best way to remove something irretrievably is to destroy the media
it's on with acid, melt it down, or the like.  For cheap removable media
like floppy disks, this is the preferred method.  However, hard drives
are expensive and hard to melt, so the @command{shred} utility tries
to achieve a similar effect non-destructively.

This uses many overwrite passes, with the data patterns chosen to
maximize the damage they do to the old data.  While this will work on
floppies, the patterns are designed for best effect on hard drives.
For more details, see the source code and Peter Gutmann's paper
@uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
@cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
from the proceedings of the Sixth USENIX Security Symposium (San Jose,
California, July 22--25, 1996).

@strong{Please note} that @command{shred} relies on a very important assumption:
that the file system overwrites data in place.  This is the traditional
way to do things, but many modern file system designs do not satisfy this
assumption.  Exceptions include:

@itemize @bullet

@item
Log-structured or journaled file systems, such as those supplied with
AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
BFS, NTFS, etc., when they are configured to journal @emph{data}.

@item
File systems that write redundant data and carry on even if some writes
fail, such as RAID-based file systems.

@item
File systems that make snapshots, such as Network Appliance's NFS server.

@item
File systems that cache in temporary locations, such as NFS version 3
clients.

@item
Compressed file systems.
@end itemize

In the particular case of ext3 file systems, the above disclaimer applies (and
@command{shred} is thus of limited effectiveness) only in @code{data=journal}
mode, which journals file data in addition to just metadata.  In both
the @code{data=ordered} (default) and @code{data=writeback} modes,
@command{shred} works as usual.  Ext3 journaling modes can be changed
by adding the @code{data=something} option to the mount options for a
particular file system in the @file{/etc/fstab} file, as documented in
the mount man page (man mount).

If you are not sure how your file system operates, then you should assume
that it does not overwrite data in place, which means that shred cannot
reliably operate on regular files in your file system.

Generally speaking, it is more reliable to shred a device than a file,
since this bypasses the problem of file system design mentioned above.
However, even shredding devices is not always completely reliable.  For
example, most disks map out bad sectors invisibly to the application; if
the bad sectors contain sensitive data, @command{shred} won't be able to
destroy it.

@command{shred} makes no attempt to detect or report this problem, just as
it makes no attempt to do anything about backups.  However, since it is
more reliable to shred devices than files, @command{shred} by default does
not truncate or remove the output file.  This default is more suitable
for devices, which typically cannot be truncated and should not be
removed.

Finally, consider the risk of backups and mirrors.
File system backups and remote mirrors may contain copies of the
file that cannot be removed, and that will allow a shredded file
to be recovered later.  So if you keep any data you may later want
to destroy using @command{shred}, be sure that it is not backed up or mirrored.

@example
shred [@var{option}]@dots{} @var{file}[@dots{}]
@end example

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -f
@itemx --force
@opindex -f
@opindex --force
@cindex force deletion
Override file permissions if necessary to allow overwriting.

@item -n @var{number}
@itemx --iterations=@var{number}
@opindex -n @var{number}
@opindex --iterations=@var{number}
@cindex iterations, selecting the number of
By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
overwrite.  You can reduce this to save time, or increase it if you think it's
appropriate.  After 25 passes all of the internal overwrite patterns will have
been used at least once.

@item --random-source=@var{file}
@opindex --random-source
@cindex random source for shredding
Use @var{file} as a source of random data used to overwrite and to
choose pass ordering.  @xref{Random sources}.

@item -s @var{bytes}
@itemx --size=@var{bytes}
@opindex -s @var{bytes}
@opindex --size=@var{bytes}
@cindex size of file to shred
Shred the first @var{bytes} bytes of the file.  The default is to shred
the whole file.  @var{bytes} can be followed by a size specification like
@samp{K}, @samp{M}, or @samp{G} to specify a multiple.  @xref{Block size}.

@item -u
@itemx --remove[=@var{how}]
@opindex -u
@opindex --remove
@opindex --remove=unlink
@opindex --remove=wipe
@opindex --remove=wipesync
@cindex removing files after shredding
After shredding a file, truncate it (if possible) and then remove it.
If a file has multiple links, only the named links will be removed.
Often the file name is less sensitive than the file data, in which case
the optional @var{how} parameter, supported with the long form option,
gives control of how to more efficiently remove each directory entry.
The @samp{unlink} parameter will just use a standard unlink call,
@samp{wipe} will also first obfuscate bytes in the name, and
@samp{wipesync} will also sync each obfuscated byte in the name to disk.
Note @samp{wipesync} is the default method, but can be expensive,
requiring a sync for every character in every file.  This can become
significant with many files, or is redundant if your file system provides
synchronous metadata updates.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Display to standard error all status updates as sterilization proceeds.

@item -x
@itemx --exact
@opindex -x
@opindex --exact
By default, @command{shred} rounds the size of a regular file up to the next
multiple of the file system block size to fully erase the slack space in
the last block of the file.  This space may contain portions of the current
system memory on some systems for example.
Use @option{--exact} to suppress that behavior.
Thus, by default if you shred a 10-byte regular file on a system with 512-byte
blocks, the resulting file will be 512 bytes long.  With this option,
shred does not increase the apparent size of the file.

@item -z
@itemx --zero
@opindex -z
@opindex --zero
Normally, the last pass that @command{shred} writes is made up of
random data.  If this would be conspicuous on your hard drive (for
example, because it looks like encrypted data), or you just think
it's tidier, the @option{--zero} option adds an additional overwrite pass with
all zero bits.  This is in addition to the number of passes specified
by the @option{--iterations} option.

@end table

You might use the following command to erase all trace of the
file system you'd created on the floppy disk in your first drive.
That command takes about 20 minutes to erase a ``1.44MB'' (actually
1440 KiB) floppy.

@example
shred --verbose /dev/fd0
@end example

Similarly, to erase all data on a selected partition of
your hard disk, you could give a command like this:

@example
shred --verbose /dev/sda5
@end example

On modern disks, a single pass should be adequate,
and it will take one third the time of the default three-pass approach.

@example
# 1 pass, write pseudo-random data; 3x faster than the default
shred --verbose -n1 /dev/sda5
@end example

To be on the safe side, use at least one pass that overwrites using
pseudo-random data.  I.e., don't be tempted to use @samp{-n0 --zero},
in case some disk controller optimizes the process of writing blocks
of all zeros, and thereby does not clear all bytes in a block.
Some SSDs may do just that.

A @var{file} of @samp{-} denotes standard output.
The intended use of this is to shred a removed temporary file.
For example:

@example
i=$(mktemp)
exec 3<>"$i"
rm -- "$i"
echo "Hello, world" >&3
shred - >&3
exec 3>-
@end example

However, the command @samp{shred - >file} does not shred the contents
of @var{file}, since the shell truncates @var{file} before invoking
@command{shred}.  Use the command @samp{shred file} or (if using a
Bourne-compatible shell) the command @samp{shred - 1<>file} instead.

@exitstatus


@node Special file types
@chapter Special file types

@cindex special file types
@cindex file types, special

This chapter describes commands which create special types of files (and
@command{rmdir}, which removes directories, one special file type).

@cindex special file types
@cindex file types
Although Unix-like operating systems have markedly fewer special file
types than others, not @emph{everything} can be treated only as the
undifferentiated byte stream of @dfn{normal files}.  For example, when a
file is created or removed, the system must record this information,
which it does in a @dfn{directory}---a special type of file.  Although
you can read directories as normal files, if you're curious, in order
for the system to do its job it must impose a structure, a certain
order, on the bytes of the file.  Thus it is a ``special'' type of file.

Besides directories, other special file types include named pipes
(FIFOs), symbolic links, sockets, and so-called @dfn{special files}.

@menu
* link invocation::             Make a hard link via the link syscall
* ln invocation::               Make links between files.
* mkdir invocation::            Make directories.
* mkfifo invocation::           Make FIFOs (named pipes).
* mknod invocation::            Make block or character special files.
* readlink invocation::         Print value of a symlink or canonical file name.
* rmdir invocation::            Remove empty directories.
* unlink invocation::           Remove files via the unlink syscall
@end menu


@node link invocation
@section @command{link}: Make a hard link via the link syscall

@pindex link
@cindex links, creating
@cindex hard links, creating
@cindex creating links (hard only)

@command{link} creates a single hard link at a time.
It is a minimalist interface to the system-provided
@code{link} function.  @xref{Hard Links, , , libc,
The GNU C Library Reference Manual}.
It avoids the bells and whistles of the more commonly-used
@command{ln} command (@pxref{ln invocation}).
Synopsis:

@example
link @var{filename} @var{linkname}
@end example

@var{filename} must specify an existing file, and @var{linkname}
must specify a nonexistent entry in an existing directory.
@command{link} simply calls @code{link (@var{filename}, @var{linkname})}
to create the link.

On a GNU system, this command acts like @samp{ln --directory
--no-target-directory @var{filename} @var{linkname}}.  However, the
@option{--directory} and @option{--no-target-directory} options are
not specified by POSIX, and the @command{link} command is
more portable in practice.

If @var{filename} is a symbolic link, it is unspecified whether
@var{linkname} will be a hard link to the symbolic link or to the
target of the symbolic link.  Use @command{ln -P} or @command{ln -L}
to specify which behavior is desired.

@exitstatus


@node ln invocation
@section @command{ln}: Make links between files

@pindex ln
@cindex links, creating
@cindex hard links, creating
@cindex symbolic (soft) links, creating
@cindex creating links (hard or soft)

@cindex file systems and hard links
@command{ln} makes links between files.  By default, it makes hard links;
with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
Synopses:

@example
ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
ln [@var{option}]@dots{} @var{target}
ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
@end example

@itemize @bullet

@item
If two file names are given, @command{ln} creates a link to the first
file from the second.

@item
If one @var{target} is given, @command{ln} creates a link to that file
in the current directory.

@item
If the @option{--target-directory} (@option{-t}) option is given, or
failing that if the last file is a directory and the
@option{--no-target-directory} (@option{-T}) option is not given,
@command{ln} creates a link to each @var{target} file in the specified
directory, using the @var{target}s' names.

@end itemize

Normally @command{ln} does not remove existing files.  Use the
@option{--force} (@option{-f}) option to remove them unconditionally,
the @option{--interactive} (@option{-i}) option to remove them
conditionally, and the @option{--backup} (@option{-b}) option to
rename them.

@cindex hard link, defined
@cindex inode, and hard links
A @dfn{hard link} is another name for an existing file; the link and the
original are indistinguishable.  Technically speaking, they share the
same inode, and the inode contains all the information about a
file---indeed, it is not incorrect to say that the inode @emph{is} the
file.  Most systems prohibit making a hard link to
a directory; on those where it is allowed, only the super-user can do
so (and with caution, since creating a cycle will cause problems to many
other utilities).  Hard links cannot cross file system boundaries.  (These
restrictions are not mandated by POSIX, however.)

@cindex dereferencing symbolic links
@cindex symbolic link, defined
@dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
a special file type (which not all kernels support: System V release 3
(and older) systems lack symlinks) in which the link file actually
refers to a different file, by name.  When most operations (opening,
reading, writing, and so on) are passed the symbolic link file, the
kernel automatically @dfn{dereferences} the link and operates on the
target of the link.  But some operations (e.g., removing) work on the
link file itself, rather than on its target.  The owner and group of a
symlink are not significant to file access performed through
the link, but do have implications on deleting a symbolic link from a
directory with the restricted deletion bit set.  On the GNU system,
the mode of a symlink has no significance and cannot be changed, but
on some BSD systems, the mode can be changed and will affect whether
the symlink will be traversed in file name resolution.  @xref{Symbolic Links,,,
libc, The GNU C Library Reference Manual}.

Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
occurs when the string in the symlink does not resolve to a file.
There are no restrictions against creating dangling symbolic links.
There are trade-offs to using absolute or relative symlinks.  An
absolute symlink always points to the same file, even if the directory
containing the link is moved.  However, if the symlink is visible from
more than one machine (such as on a networked file system), the file
pointed to might not always be the same.  A relative symbolic link is
resolved in relation to the directory that contains the link, and is
often useful in referring to files on the same device without regards
to what name that device is mounted on when accessed via networked
machines.

When creating a relative symlink in a different location than the
current directory, the resolution of the symlink will be different
than the resolution of the same string from the current directory.
Therefore, many users prefer to first change directories to the
location where the relative symlink will be created, so that
tab-completion or other file resolution will find the same target as
what will be placed in the symlink.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@optBackup

@item -d
@itemx -F
@itemx --directory
@opindex -d
@opindex -F
@opindex --directory
@cindex hard links to directories
Allow users with appropriate privileges to attempt to make hard links
to directories.
However, note that this will probably fail due to
system restrictions, even for the super-user.

@item -f
@itemx --force
@opindex -f
@opindex --force
Remove existing destination files.

@item -i
@itemx --interactive
@opindex -i
@opindex --interactive
@cindex prompting, and @command{ln}
Prompt whether to remove existing destination files.

@item -L
@itemx --logical
@opindex -L
@opindex --logical
If @option{-s} is not in effect, and the source file is a symbolic
link, create the hard link to the file referred to by the symbolic
link, rather than the symbolic link itself.

@item -n
@itemx --no-dereference
@opindex -n
@opindex --no-dereference
Do not treat the last operand specially when it is a symbolic link to
a directory.  Instead, treat it as if it were a normal file.

When the destination is an actual directory (not a symlink to one),
there is no ambiguity.  The link is created in that directory.
But when the specified destination is a symlink to a directory,
there are two ways to treat the user's request.  @command{ln} can
treat the destination just as it would a normal directory and create
the link in it.  On the other hand, the destination can be viewed as a
non-directory---as the symlink itself.  In that case, @command{ln}
must delete or backup that symlink before creating the new link.
The default is to treat a destination that is a symlink to a directory
just like a directory.

This option is weaker than the @option{--no-target-directory}
(@option{-T}) option, so it has no effect if both options are given.

@item -P
@itemx --physical
@opindex -P
@opindex --physical
If @option{-s} is not in effect, and the source file is a symbolic
link, create the hard link to the symbolic link itself.  On platforms
where this is not supported by the kernel, this option creates a
symbolic link with identical contents; since symbolic link contents
cannot be edited, any file name resolution performed through either
link will be the same as if a hard link had been created.

@item -r
@itemx --relative
@opindex -r
@opindex --relative
Make symbolic links relative to the link location.

Example:

@smallexample
ln -srv /a/file /tmp
'/tmp/file' -> '../a/file'
@end smallexample

Relative symbolic links are generated based on their canonicalized
containing directory, and canonicalized targets.  I.e., all symbolic
links in these file names will be resolved.
@xref{realpath invocation}, which gives greater control
over relative file name generation, as demonstrated in the following example:

@example
@verbatim
ln--relative() {
  test "$1" = --no-symlinks && { nosym=$1; shift; }
  target="$1";
  test -d "$2" && link="$2/." || link="$2"
  rtarget="$(realpath $nosym -m "$target" \
              --relative-to "$(dirname "$link")")"
  ln -s -v "$rtarget" "$link"
}
@end verbatim
@end example

@item -s
@itemx --symbolic
@opindex -s
@opindex --symbolic
Make symbolic links instead of hard links.  This option merely produces
an error message on systems that do not support symbolic links.

@optBackupSuffix

@optTargetDirectory

@optNoTargetDirectory

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Print the name of each file after linking it successfully.

@end table

@cindex hard links to symbolic links
@cindex symbolic links and @command{ln}
If @option{-L} and @option{-P} are both given, the last one takes
precedence.  If @option{-s} is also given, @option{-L} and @option{-P}
are silently ignored.  If neither option is given, then this
implementation defaults to @option{-P} if the system @code{link} supports
hard links to symbolic links (such as the GNU system), and @option{-L}
if @code{link} follows symbolic links (such as on BSD).

@exitstatus

Examples:

@smallexample
Bad Example:

# Create link ../a pointing to a in that directory.
# Not really useful because it points to itself.
ln -s a ..

Better Example:

# Change to the target before creating symlinks to avoid being confused.
cd ..
ln -s adir/a .

Bad Example:

# Hard coded file names don't move well.
ln -s $(pwd)/a /some/dir/

Better Example:

# Relative file names survive directory moves and also
# work across networked file systems.
ln -s afile anotherfile
ln -s ../adir/afile yetanotherfile
@end smallexample


@node mkdir invocation
@section @command{mkdir}: Make directories

@pindex mkdir
@cindex directories, creating
@cindex creating directories

@command{mkdir} creates directories with the specified names.  Synopsis:

@example
mkdir [@var{option}]@dots{} @var{name}@dots{}
@end example

@command{mkdir} creates each directory @var{name} in the order given.
It reports an error if @var{name} already exists, unless the
@option{-p} option is given and @var{name} is a directory.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -m @var{mode}
@itemx --mode=@var{mode}
@opindex -m
@opindex --mode
@cindex modes of created directories, setting
Set the file permission bits of created directories to @var{mode},
which uses the same syntax as
in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
everyone) for the point of the departure.  @xref{File permissions}.

Normally the directory has the desired file mode bits at the moment it
is created.  As a GNU extension, @var{mode} may also mention
special mode bits, but in this case there may be a temporary window
during which the directory exists but its special mode bits are
incorrect.  @xref{Directory Setuid and Setgid}, for how the
set-user-ID and set-group-ID bits of directories are inherited unless
overridden in this way.

@item -p
@itemx --parents
@opindex -p
@opindex --parents
@cindex parent directories, creating
Make any missing parent directories for each argument, setting their
file permission bits to the umask modified by @samp{u+wx}.  Ignore
existing parent directories, and do not change their file permission
bits.

To set the file permission bits of any newly-created parent
directories to a value that includes @samp{u+wx}, you can set the
umask before invoking @command{mkdir}.  For example, if the shell
command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
@file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
To set a parent's special mode bits as well, you can invoke
@command{chmod} after @command{mkdir}.  @xref{Directory Setuid and
Setgid}, for how the set-user-ID and set-group-ID bits of
newly-created parent directories are inherited.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Print a message for each created directory.  This is most useful with
@option{--parents}.

@optContext

@end table

@exitstatus


@node mkfifo invocation
@section @command{mkfifo}: Make FIFOs (named pipes)

@pindex mkfifo
@cindex FIFOs, creating
@cindex named pipes, creating
@cindex creating FIFOs (named pipes)

@command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
specified names.  Synopsis:

@example
mkfifo [@var{option}] @var{name}@dots{}
@end example

A @dfn{FIFO} is a special file type that permits independent processes
to communicate.  One process opens the FIFO file for writing, and
another for reading, after which data can flow as with the usual
anonymous pipe in shells or elsewhere.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -m @var{mode}
@itemx --mode=@var{mode}
@opindex -m
@opindex --mode
@cindex modes of created FIFOs, setting
Set the mode of created FIFOs to @var{mode}, which is symbolic as in
@command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
for the point of departure.  @var{mode} should specify only file
permission bits.  @xref{File permissions}.

@optContext

@end table

@exitstatus


@node mknod invocation
@section @command{mknod}: Make block or character special files

@pindex mknod
@cindex block special files, creating
@cindex character special files, creating

@command{mknod} creates a FIFO, character special file, or block special
file with the specified name.  Synopsis:

@example
mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
@end example

@cindex special files
@cindex block special files
@cindex character special files
Unlike the phrase ``special file type'' above, the term @dfn{special
file} has a technical meaning on Unix: something that can generate or
receive data.  Usually this corresponds to a physical piece of hardware,
e.g., a printer or a disk.  (These files are typically created at
system-configuration time.)  The @command{mknod} command is what creates
files of this type.  Such devices can be read either a character at a
time or a ``block'' (many characters) at a time, hence we say there are
@dfn{block special} files and @dfn{character special} files.

@c mknod is a shell built-in at least with OpenBSD's /bin/sh
@mayConflictWithShellBuiltIn{mknod}

The arguments after @var{name} specify the type of file to make:

@table @samp

@item p
@opindex p @r{for FIFO file}
for a FIFO

@item b
@opindex b @r{for block special file}
for a block special file

@item c
@c Don't document the 'u' option -- it's just a synonym for 'c'.
@c Do *any* versions of mknod still use it?
@c @itemx u
@opindex c @r{for character special file}
@c @opindex u @r{for character special file}
for a character special file

@end table

When making a block or character special file, the major and minor
device numbers must be given after the file type.
If a major or minor device number begins with @samp{0x} or @samp{0X},
it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
as octal; otherwise, as decimal.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -m @var{mode}
@itemx --mode=@var{mode}
@opindex -m
@opindex --mode
Set the mode of created files to @var{mode}, which is symbolic as in
@command{chmod} and uses @samp{a=rw} as the point of departure.
@var{mode} should specify only file permission bits.
@xref{File permissions}.

@optContext

@end table

@exitstatus


@node readlink invocation
@section @command{readlink}: Print value of a symlink or canonical file name

@pindex readlink
@cindex displaying value of a symbolic link
@cindex canonical file name
@cindex canonicalize a file name
@findex realpath

@command{readlink} may work in one of two supported modes:

@table @samp

@item Readlink mode

@command{readlink} outputs the value of the given symbolic links.
If @command{readlink} is invoked with an argument other than the name
of a symbolic link, it produces no output and exits with a nonzero exit code.

@item Canonicalize mode

@command{readlink} outputs the absolute name of the given files which contain
no @file{.}, @file{..} components nor any repeated separators
(@file{/}) or symbolic links.

@end table

@example
readlink [@var{option}]@dots{} @var{file}@dots{}
@end example

By default, @command{readlink} operates in readlink mode.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -f
@itemx --canonicalize
@opindex -f
@opindex --canonicalize
Activate canonicalize mode.
If any component of the file name except the last one is missing or unavailable,
@command{readlink} produces no output and exits with a nonzero exit
code.  A trailing slash is ignored.

@item -e
@itemx --canonicalize-existing
@opindex -e
@opindex --canonicalize-existing
Activate canonicalize mode.
If any component is missing or unavailable, @command{readlink} produces
no output and exits with a nonzero exit code.  A trailing slash
requires that the name resolve to a directory.

@item -m
@itemx --canonicalize-missing
@opindex -m
@opindex --canonicalize-missing
Activate canonicalize mode.
If any component is missing or unavailable, @command{readlink} treats it
as a directory.

@item -n
@itemx --no-newline
@opindex -n
@opindex --no-newline
Do not print the output delimiter, when a single @var{file} is specified.
Print a warning if specified along with multiple @var{file}s.

@item -s
@itemx -q
@itemx --silent
@itemx --quiet
@opindex -s
@opindex -q
@opindex --silent
@opindex --quiet
Suppress most error messages.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Report error messages.

@optZero

@end table

The @command{readlink} utility first appeared in OpenBSD 2.1.

The @command{realpath} command without options, operates like
@command{readlink} in canonicalize mode.

@exitstatus


@node rmdir invocation
@section @command{rmdir}: Remove empty directories

@pindex rmdir
@cindex removing empty directories
@cindex directories, removing empty

@command{rmdir} removes empty directories.  Synopsis:

@example
rmdir [@var{option}]@dots{} @var{directory}@dots{}
@end example

If any @var{directory} argument does not refer to an existing empty
directory, it is an error.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item --ignore-fail-on-non-empty
@opindex --ignore-fail-on-non-empty
@cindex directory deletion, ignoring failures
Ignore each failure to remove a directory that is solely because
the directory is non-empty.

@item -p
@itemx --parents
@opindex -p
@opindex --parents
@cindex parent directories, removing
Remove @var{directory}, then try to remove each component of @var{directory}.
So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
As such, it fails if any of those directories turns out not to be empty.
Use the @option{--ignore-fail-on-non-empty} option to make it so such
a failure does not evoke a diagnostic and does not cause @command{rmdir} to
exit unsuccessfully.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
@cindex directory deletion, reporting
Give a diagnostic for each successful removal.
@var{directory} is removed.

@end table

@xref{rm invocation}, for how to remove non-empty directories (recursively).

@exitstatus


@node unlink invocation
@section @command{unlink}: Remove files via the unlink syscall

@pindex unlink
@cindex removing files or directories (via the unlink syscall)

@command{unlink} deletes a single specified file name.
It is a minimalist interface to the system-provided
@code{unlink} function.  @xref{Deleting Files, , , libc,
The GNU C Library Reference Manual}.  Synopsis:
It avoids the bells and whistles of the more commonly-used
@command{rm} command (@pxref{rm invocation}).

@example
unlink @var{filename}
@end example

On some systems @code{unlink} can be used to delete the name of a
directory.  On others, it can be used that way only by a privileged user.
In the GNU system @code{unlink} can never delete the name of a directory.

The @command{unlink} command honors the @option{--help} and
@option{--version} options.  To remove a file whose name begins with
@samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.

@exitstatus


@node Changing file attributes
@chapter Changing file attributes

@cindex changing file attributes
@cindex file attributes, changing
@cindex attributes, file

A file is not merely its contents, a name, and a file type
(@pxref{Special file types}).  A file also has an owner (a user ID), a
group (a group ID), permissions (what the owner can do with the file,
what people in the group can do, and what everyone else can do), various
timestamps, and other information.  Collectively, we call these a file's
@dfn{attributes}.

These commands change file attributes.

@menu
* chown invocation::            Change file owners and groups.
* chgrp invocation::            Change file groups.
* chmod invocation::            Change access permissions.
* touch invocation::            Change file timestamps.
@end menu


@node chown invocation
@section @command{chown}: Change file owner and group

@pindex chown
@cindex file ownership, changing
@cindex group ownership, changing
@cindex changing file ownership
@cindex changing group ownership

@command{chown} changes the user and/or group ownership of each given @var{file}
to @var{new-owner} or to the user and group of an existing reference file.
Synopsis:

@example
chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@}@c
 @var{file}@dots{}
@end example

If used, @var{new-owner} specifies the new owner and/or group as follows
(with no embedded white space):

@example
[@var{owner}] [ : [@var{group}] ]
@end example

Specifically:

@table @var
@item owner
If only an @var{owner} (a user name or numeric user ID) is given, that
user is made the owner of each given file, and the files' group is not
changed.

@item owner@samp{:}group
If the @var{owner} is followed by a colon and a @var{group} (a
group name or numeric group ID), with no spaces between them, the group
ownership of the files is changed as well (to @var{group}).

@item owner@samp{:}
If a colon but no group name follows @var{owner}, that user is
made the owner of the files and the group of the files is changed to
@var{owner}'s login group.

@item @samp{:}group
If the colon and following @var{group} are given, but the owner
is omitted, only the group of the files is changed; in this case,
@command{chown} performs the same function as @command{chgrp}.

@item @samp{:}
If only a colon is given, or if @var{new-owner} is empty, neither the
owner nor the group is changed.

@end table

If @var{owner} or @var{group} is intended to represent a numeric user
or group ID, then you may specify it with a leading @samp{+}.
@xref{Disambiguating names and IDs}.

Some older scripts may still use @samp{.} in place of the @samp{:} separator.
POSIX 1003.1-2001 (@pxref{Standards conformance}) does not
require support for that, but for backward compatibility GNU
@command{chown} supports @samp{.} so long as no ambiguity results.
New scripts should avoid the use of @samp{.} because it is not
portable, and because it has undesirable results if the entire
@var{owner@samp{.}group} happens to identify a user whose name
contains @samp{.}.

@macro chownGroupRestrictions
It is system dependent whether a user can change the group to an arbitrary one,
or the more portable behavior of being restricted to setting a group of
which the user is a member.
@end macro
@chownGroupRestrictions

The @command{chown} command sometimes clears the set-user-ID or
set-group-ID permission bits.  This behavior depends on the policy and
functionality of the underlying @code{chown} system call, which may
make system-dependent file mode modifications outside the control of
the @command{chown} command.  For example, the @command{chown} command
might not affect those bits when invoked by a user with appropriate
privileges, or when the
bits signify some function other than executable permission (e.g.,
mandatory locking).
When in doubt, check the underlying system behavior.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -c
@itemx --changes
@opindex -c
@opindex --changes
@cindex changed owners, verbosely describing
Verbosely describe the action for each @var{file} whose ownership
actually changes.

@item -f
@itemx --silent
@itemx --quiet
@opindex -f
@opindex --silent
@opindex --quiet
@cindex error messages, omitting
Do not print error messages about files whose ownership cannot be
changed.

@item --from=@var{old-owner}
@opindex --from
@cindex symbolic links, changing owner
Change a @var{file}'s ownership only if it has current attributes specified
by @var{old-owner}.  @var{old-owner} has the same form as @var{new-owner}
described above.
This option is useful primarily from a security standpoint in that
it narrows considerably the window of potential abuse.
For example, to reflect a user ID numbering change for one user's files
without an option like this, @code{root} might run

@smallexample
find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
@end smallexample

But that is dangerous because the interval between when the @command{find}
tests the existing file's owner and when the @command{chown} is actually run
may be quite large.
One way to narrow the gap would be to invoke chown for each file
as it is found:

@example
find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
@end example

But that is very slow if there are many affected files.
With this option, it is safer (the gap is narrower still)
though still not perfect:

@example
chown -h -R --from=OLDUSER NEWUSER /
@end example

@item --dereference
@opindex --dereference
@cindex symbolic links, changing owner
@findex lchown
Do not act on symbolic links themselves but rather on what they point to.
This is the default.

@item -h
@itemx --no-dereference
@opindex -h
@opindex --no-dereference
@cindex symbolic links, changing owner
@findex lchown
Act on symbolic links themselves instead of what they point to.
This mode relies on the @code{lchown} system call.
On systems that do not provide the @code{lchown} system call,
@command{chown} fails when a file specified on the command line
is a symbolic link.
By default, no diagnostic is issued for symbolic links encountered
during a recursive traversal, but see @option{--verbose}.

@item --preserve-root
@opindex --preserve-root
@cindex root directory, disallow recursive modification
Fail upon any attempt to recursively change the root directory, @file{/}.
Without @option{--recursive}, this option has no effect.
@xref{Treating / specially}.

@item --no-preserve-root
@opindex --no-preserve-root
@cindex root directory, allow recursive modification
Cancel the effect of any preceding @option{--preserve-root} option.
@xref{Treating / specially}.

@item --reference=@var{ref_file}
@opindex --reference
Change the user and group of each @var{file} to be the same as those of
@var{ref_file}.  If @var{ref_file} is a symbolic link, do not use the
user and group of the symbolic link, but rather those of the file it
refers to.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Output a diagnostic for every file processed.
If a symbolic link is encountered during a recursive traversal
on a system without the @code{lchown} system call, and @option{--no-dereference}
is in effect, then issue a diagnostic saying neither the symbolic link nor
its referent is being changed.

@item -R
@itemx --recursive
@opindex -R
@opindex --recursive
@cindex recursively changing file ownership
Recursively change ownership of directories and their contents.

@choptH
@xref{Traversing symlinks}.

@choptL
@xref{Traversing symlinks}.

@choptP
@xref{Traversing symlinks}.

@end table

@exitstatus

Examples:

@smallexample
# Change the owner of /u to "root".
chown root /u

# Likewise, but also change its group to "staff".
chown root:staff /u

# Change the owner of /u and subfiles to "root".
chown -hR root /u
@end smallexample


@node chgrp invocation
@section @command{chgrp}: Change group ownership

@pindex chgrp
@cindex group ownership, changing
@cindex changing group ownership

@command{chgrp} changes the group ownership of each given @var{file}
to @var{group} (which can be either a group name or a numeric group ID)
or to the group of an existing reference file.  @xref{chown invocation}.
Synopsis:

@example
chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@}@c
 @var{file}@dots{}
@end example

If @var{group} is intended to represent a
numeric group ID, then you may specify it with a leading @samp{+}.
@xref{Disambiguating names and IDs}.

@chownGroupRestrictions

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -c
@itemx --changes
@opindex -c
@opindex --changes
@cindex changed files, verbosely describing
Verbosely describe the action for each @var{file} whose group actually
changes.

@item -f
@itemx --silent
@itemx --quiet
@opindex -f
@opindex --silent
@opindex --quiet
@cindex error messages, omitting
Do not print error messages about files whose group cannot be
changed.

@item --dereference
@opindex --dereference
@cindex symbolic links, changing owner
@findex lchown
Do not act on symbolic links themselves but rather on what they point to.
This is the default.

@item -h
@itemx --no-dereference
@opindex -h
@opindex --no-dereference
@cindex symbolic links, changing group
@findex lchown
Act on symbolic links themselves instead of what they point to.
This mode relies on the @code{lchown} system call.
On systems that do not provide the @code{lchown} system call,
@command{chgrp} fails when a file specified on the command line
is a symbolic link.
By default, no diagnostic is issued for symbolic links encountered
during a recursive traversal, but see @option{--verbose}.

@item --preserve-root
@opindex --preserve-root
@cindex root directory, disallow recursive modification
Fail upon any attempt to recursively change the root directory, @file{/}.
Without @option{--recursive}, this option has no effect.
@xref{Treating / specially}.

@item --no-preserve-root
@opindex --no-preserve-root
@cindex root directory, allow recursive modification
Cancel the effect of any preceding @option{--preserve-root} option.
@xref{Treating / specially}.

@item --reference=@var{ref_file}
@opindex --reference
Change the group of each @var{file} to be the same as that of
@var{ref_file}.  If @var{ref_file} is a symbolic link, do not use the
group of the symbolic link, but rather that of the file it refers to.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Output a diagnostic for every file processed.
If a symbolic link is encountered during a recursive traversal
on a system without the @code{lchown} system call, and @option{--no-dereference}
is in effect, then issue a diagnostic saying neither the symbolic link nor
its referent is being changed.

@item -R
@itemx --recursive
@opindex -R
@opindex --recursive
@cindex recursively changing group ownership
Recursively change the group ownership of directories and their contents.

@choptH
@xref{Traversing symlinks}.

@choptL
@xref{Traversing symlinks}.

@choptP
@xref{Traversing symlinks}.

@end table

@exitstatus

Examples:

@smallexample
# Change the group of /u to "staff".
chgrp staff /u

# Change the group of /u and subfiles to "staff".
chgrp -hR staff /u
@end smallexample


@node chmod invocation
@section @command{chmod}: Change access permissions

@pindex chmod
@cindex changing access permissions
@cindex access permissions, changing
@cindex permissions, changing access

@command{chmod} changes the access permissions of the named files.  Synopsis:

@example
chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@}@c
 @var{file}@dots{}
@end example

@cindex symbolic links, permissions of
@command{chmod} never changes the permissions of symbolic links, since
the @command{chmod} system call cannot change their permissions.
This is not a problem since the permissions of symbolic links are
never used.  However, for each symbolic link listed on the command
line, @command{chmod} changes the permissions of the pointed-to file.
In contrast, @command{chmod} ignores symbolic links encountered during
recursive directory traversals.

A successful use of @command{chmod} clears the set-group-ID bit of a
regular file if the file's group ID does not match the user's
effective group ID or one of the user's supplementary group IDs,
unless the user has appropriate privileges.  Additional restrictions
may cause the set-user-ID and set-group-ID bits of @var{mode} or
@var{ref_file} to be ignored.  This behavior depends on the policy and
functionality of the underlying @code{chmod} system call.  When in
doubt, check the underlying system behavior.

If used, @var{mode} specifies the new file mode bits.
For details, see the section on @ref{File permissions}.
If you really want @var{mode} to have a leading @samp{-}, you should
use @option{--} first, e.g., @samp{chmod -- -w file}.  Typically,
though, @samp{chmod a-w file} is preferable, and @command{chmod -w
file} (without the @option{--}) complains if it behaves differently
from what @samp{chmod a-w file} would do.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -c
@itemx --changes
@opindex -c
@opindex --changes
Verbosely describe the action for each @var{file} whose permissions
actually changes.

@item -f
@itemx --silent
@itemx --quiet
@opindex -f
@opindex --silent
@opindex --quiet
@cindex error messages, omitting
Do not print error messages about files whose permissions cannot be
changed.

@item --preserve-root
@opindex --preserve-root
@cindex root directory, disallow recursive modification
Fail upon any attempt to recursively change the root directory, @file{/}.
Without @option{--recursive}, this option has no effect.
@xref{Treating / specially}.

@item --no-preserve-root
@opindex --no-preserve-root
@cindex root directory, allow recursive modification
Cancel the effect of any preceding @option{--preserve-root} option.
@xref{Treating / specially}.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
Verbosely describe the action or non-action taken for every @var{file}.

@item --reference=@var{ref_file}
@opindex --reference
Change the mode of each @var{file} to be the same as that of @var{ref_file}.
@xref{File permissions}.
If @var{ref_file} is a symbolic link, do not use the mode
of the symbolic link, but rather that of the file it refers to.

@item -R
@itemx --recursive
@opindex -R
@opindex --recursive
@cindex recursively changing access permissions
Recursively change permissions of directories and their contents.

@end table

@exitstatus


@node touch invocation
@section @command{touch}: Change file timestamps

@pindex touch
@cindex changing file timestamps
@cindex file timestamps, changing
@cindex timestamps, changing file

@command{touch} changes the access and/or modification times of the
specified files.  Synopsis:

@example
touch [@var{option}]@dots{} @var{file}@dots{}
@end example

@cindex empty files, creating
Any @var{file} argument that does not exist is created empty, unless
option @option{--no-create} (@option{-c}) or @option{--no-dereference}
(@option{-h}) was in effect.

A @var{file} argument string of @samp{-} is handled specially and
causes @command{touch} to change the times of the file associated with
standard output.

@cindex clock skew
By default, @command{touch} sets file timestamps to the current time.
Because @command{touch} acts on its operands left to right, the
resulting timestamps of earlier and later operands may disagree.
Also, the determination of what time is ``current'' depends on the
platform.  Platforms with network file systems often use different
clocks for the operating system and for file systems; because
@command{touch} typically uses file systems' clocks by default, clock
skew can cause the resulting file timestamps to appear to be in a
program's ``future'' or ``past''.

@cindex file timestamp resolution
The @command{touch} command sets the file's timestamp to the greatest
representable value that is not greater than the requested time.  This
can differ from the requested time for several reasons.  First, the
requested time may have a higher resolution than supported.  Second, a
file system may use different resolutions for different types of
times.  Third, file timestamps may use a different resolution than
operating system timestamps.  Fourth, the operating system primitives
used to update timestamps may employ yet a different resolution.  For
example, in theory a file system might use 10-microsecond resolution
for access time and 100-nanosecond resolution for modification time,
and the operating system might use nanosecond resolution for the
current time and microsecond resolution for the primitive that
@command{touch} uses to set a file's timestamp to an arbitrary value.

@cindex permissions, for changing file timestamps
When setting file timestamps to the current time, @command{touch} can
change the timestamps for files that the user does not own but has
write permission for.  Otherwise, the user must own the files.  Some
older systems have a further restriction: the user must own the files
unless both the access and modification times are being set to the
current time.

Although @command{touch} provides options for changing two of the times---the
times of last access and modification---of a file, there is actually
a standard third one as well: the inode change time.  This is often
referred to as a file's @code{ctime}.
The inode change time represents the time when the file's meta-information
last changed.  One common example of this is when the permissions of a
file change.  Changing the permissions doesn't access the file, so
the atime doesn't change, nor does it modify the file, so the mtime
doesn't change.  Yet, something about the file itself has changed,
and this must be noted somewhere.  This is the job of the ctime field.
This is necessary, so that, for example, a backup program can make a
fresh copy of the file, including the new permissions value.
Another operation that modifies a file's ctime without affecting
the others is renaming.  In any case, it is not possible, in normal
operations, for a user to change the ctime field to a user-specified value.
Some operating systems and file systems support a fourth time: the
birth time, when the file was first created; by definition, this
timestamp never changes.

@vindex TZ
Time stamps assume the time zone rules specified by the @env{TZ}
environment variable, or by the system default rules if @env{TZ} is
not set.  @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
libc, The GNU C Library Reference Manual}.
You can avoid ambiguities during
daylight saving transitions by using UTC time stamps.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -a
@itemx --time=atime
@itemx --time=access
@itemx --time=use
@opindex -a
@opindex --time
@opindex atime@r{, changing}
@opindex access @r{time, changing}
@opindex use @r{time, changing}
Change the access time only.

@item -c
@itemx --no-create
@opindex -c
@opindex --no-create
Do not warn about or create files that do not exist.

@item -d @var{time}
@itemx --date=@var{time}
@opindex -d
@opindex --date
@opindex time
Use @var{time} instead of the current time.  It can contain month names,
time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc.  For
example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
specifies the instant of time that is 489,392,193 nanoseconds after
February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
minutes east of UTC@.  @xref{Date input formats}.
File systems that do not support high-resolution time stamps
silently ignore any excess precision here.

@item -f
@opindex -f
@cindex BSD @command{touch} compatibility
Ignored; for compatibility with BSD versions of @command{touch}.

@item -h
@itemx --no-dereference
@opindex -h
@opindex --no-dereference
@cindex symbolic links, changing time
@findex lutimes
Attempt to change the timestamps of a symbolic link, rather than what
the link refers to.  When using this option, empty files are not
created, but option @option{-c} must also be used to avoid warning
about files that do not exist.  Not all systems support changing the
timestamps of symlinks, since underlying system support for this
action was not required until POSIX 2008.  Also, on some
systems, the mere act of examining a symbolic link changes the access
time, such that only changes to the modification time will persist
long enough to be observable.  When coupled with option @option{-r}, a
reference timestamp is taken from a symbolic link rather than the file
it refers to.

@item -m
@itemx --time=mtime
@itemx --time=modify
@opindex -m
@opindex --time
@opindex mtime@r{, changing}
@opindex modify @r{time, changing}
Change the modification time only.

@item -r @var{file}
@itemx --reference=@var{file}
@opindex -r
@opindex --reference
Use the times of the reference @var{file} instead of the current time.
If this option is combined with the @option{--date=@var{time}}
(@option{-d @var{time}}) option, the reference @var{file}'s time is
the origin for any relative @var{time}s given, but is otherwise ignored.
For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
equal to five seconds before the corresponding time stamp for @file{foo}.
If @var{file} is a symbolic link, the reference timestamp is taken
from the target of the symlink, unless @option{-h} was also in effect.

@item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
@cindex leap seconds
Use the argument (optional four-digit or two-digit years, months,
days, hours, minutes, optional seconds) instead of the current time.
If the year is specified with only two digits, then @var{cc}
is 20 for years in the range 0 @dots{} 68, and 19 for years in
69 @dots{} 99.  If no digits of the year are specified,
the argument is interpreted as a date in the current year.
On the atypical systems that support leap seconds, @var{ss} may be
@samp{60}.

@end table

@vindex _POSIX2_VERSION
On systems predating POSIX 1003.1-2001,
@command{touch} supports an obsolete syntax, as follows.
If no timestamp is given with any of the @option{-d}, @option{-r}, or
@option{-t} options, and if there are two or more @var{file}s and the
first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
would be a valid argument to the @option{-t} option (if the @var{yy}, if
any, were moved to the front), and if the represented year
is in the range 1969--1999, that argument is interpreted as the time
for the other files instead of as a file name.
Although this obsolete behavior can be controlled with the
@env{_POSIX2_VERSION} environment variable (@pxref{Standards
conformance}), portable scripts should avoid commands whose
behavior depends on this variable.
For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.

@exitstatus


@node Disk usage
@chapter Disk usage

@cindex disk usage

No disk can hold an infinite amount of data.  These commands report
how much disk storage is in use or available, report other file and
file status information, and write buffers to disk.

@menu
* df invocation::               Report file system disk space usage.
* du invocation::               Estimate file space usage.
* stat invocation::             Report file or file system status.
* sync invocation::             Synchronize cached writes to persistent storage.
* truncate invocation::         Shrink or extend the size of a file.
@end menu


@node df invocation
@section @command{df}: Report file system disk space usage

@pindex df
@cindex file system disk usage
@cindex disk usage by file system

@command{df} reports the amount of disk space used and available on
file systems.  Synopsis:

@example
df [@var{option}]@dots{} [@var{file}]@dots{}
@end example

With no arguments, @command{df} reports the space used and available on all
currently mounted file systems (of all types).  Otherwise, @command{df}
reports on the file system containing each argument @var{file}.

Normally the disk space is printed in units of
1024 bytes, but this can be overridden (@pxref{Block size}).
Non-integer quantities are rounded up to the next higher unit.

For bind mounts and without arguments, @command{df} only outputs the statistics
for that device with the shortest mount point name in the list of file systems
(@var{mtab}), i.e., it hides duplicate entries, unless the @option{-a} option is
specified.

With the same logic, @command{df} elides a mount entry of a dummy pseudo device
if there is another mount entry of a real block device for that mount point with
the same device number, e.g. the early-boot pseudo file system @samp{rootfs} is
not shown per default when already the real root device has been mounted.

@cindex disk device file
@cindex device file, disk
If an argument @var{file} resolves to a special file containing
a mounted file system, @command{df} shows the space available on that
file system rather than on the file system containing the device node.
GNU @command{df} does not attempt to determine the disk usage
on unmounted file systems, because on most kinds of systems doing so
requires extremely nonportable intimate knowledge of file system structures.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -a
@itemx --all
@opindex -a
@opindex --all
@cindex ignore file systems
Include in the listing dummy, duplicate, or inaccessible file systems, which
are omitted by default.  Dummy file systems are typically special purpose
pseudo file systems such as @samp{/proc}, with no associated storage.
Duplicate file systems are local or remote file systems that are mounted
at separate locations in the local file hierarchy, or bind mounted locations.
Inaccessible file systems are those which are mounted but subsequently
over-mounted by another file system at that point, or otherwise inaccessible
due to permissions of the mount point etc.

@item -B @var{size}
@itemx --block-size=@var{size}
@opindex -B
@opindex --block-size
@cindex file system sizes
Scale sizes by @var{size} before printing them (@pxref{Block size}).
For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.

@optHumanReadable

@item -H
@opindex -H
Equivalent to @option{--si}.

@item -i
@itemx --inodes
@opindex -i
@opindex --inodes
@cindex inode usage
List inode usage information instead of block usage.  An inode (short
for index node) contains information about a file such as its owner,
permissions, timestamps, and location on the disk.

@item -k
@opindex -k
@cindex kibibytes for file system sizes
Print sizes in 1024-byte blocks, overriding the default block size
(@pxref{Block size}).
This option is equivalent to @option{--block-size=1K}.

@item -l
@itemx --local
@opindex -l
@opindex --local
@cindex file system types, limiting output to certain
Limit the listing to local file systems.  By default, remote file systems
are also listed.

@item --no-sync
@opindex --no-sync
@cindex file system space, retrieving old data more quickly
Do not invoke the @code{sync} system call before getting any usage data.
This may make @command{df} run significantly faster on systems with many
disks, but on some systems (notably SunOS) the results may be slightly
out of date.  This is the default.

@item --output
@itemx --output[=@var{field_list}]
@opindex --output
Use the output format defined by @var{field_list}, or print all fields if
@var{field_list} is omitted.  In the latter case, the order of the columns
conforms to the order of the field descriptions below.

The use of the @option{--output} together with each of the options @option{-i},
@option{-P}, and @option{-T} is mutually exclusive.

FIELD_LIST is a comma-separated list of columns to be included in @command{df}'s
output and therefore effectively controls the order of output columns.
Each field can thus be used at the place of choice, but yet must only be
used once.

Valid field names in the @var{field_list} are:
@table @samp
@item source
The source of the mount point, usually a device.
@item fstype
File system type.

@item itotal
Total number of inodes.
@item iused
Number of used inodes.
@item iavail
Number of available inodes.
@item ipcent
Percentage of @var{iused} divided by @var{itotal}.

@item size
Total number of blocks.
@item used
Number of used blocks.
@item avail
Number of available blocks.
@item pcent
Percentage of @var{used} divided by @var{size}.

@item file
The file name if specified on the command line.
@item target
The mount point.
@end table

The fields for block and inodes statistics are affected by the scaling
options like @option{-h} as usual.

The definition of the @var{field_list} can even be split among several
@option{--output} uses.

@example
#!/bin/sh
# Print the TARGET (i.e., the mount point) along with their percentage
# statistic regarding the blocks and the inodes.
df --out=target --output=pcent,ipcent

# Print all available fields.
df --o
@end example


@item -P
@itemx --portability
@opindex -P
@opindex --portability
@cindex one-line output format
@cindex POSIX output format
@cindex portable output format
@cindex output format, portable
Use the POSIX output format.  This is like the default format except
for the following:

@enumerate
@item
The information about each file system is always printed on exactly
one line; a mount device is never put on a line by itself.  This means
that if the mount device name is more than 20 characters long (e.g., for
some network mounts), the columns are misaligned.

@item
The labels in the header output line are changed to conform to POSIX.

@item
The default block size and output format are unaffected by the
@env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
variables.  However, the default block size is still affected by
@env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
otherwise.  @xref{Block size}.
@end enumerate

@optSi

@item --sync
@opindex --sync
@cindex file system space, retrieving current data more slowly
Invoke the @code{sync} system call before getting any usage data.  On
some systems (notably SunOS), doing this yields more up to date results,
but in general this option makes @command{df} much slower, especially when
there are many or very busy file systems.

@item --total
@opindex --total
@cindex grand total of disk size, usage and available space
Print a grand total of all arguments after all arguments have
been processed.  This can be used to find out the total disk size, usage
and available space of all listed devices.  If no arguments are specified
df will try harder to elide file systems insignificant to the total
available space, by suppressing duplicate remote file systems.

For the grand total line, @command{df} prints @samp{"total"} into the
@var{source} column, and @samp{"-"} into the @var{target} column.
If there is no @var{source} column (see @option{--output}), then
@command{df} prints @samp{"total"} into the @var{target} column,
if present.

@item -t @var{fstype}
@itemx --type=@var{fstype}
@opindex -t
@opindex --type
@cindex file system types, limiting output to certain
Limit the listing to file systems of type @var{fstype}.  Multiple
file system types can be specified by giving multiple @option{-t} options.
By default, nothing is omitted.

@item -T
@itemx --print-type
@opindex -T
@opindex --print-type
@cindex file system types, printing
Print each file system's type.  The types printed here are the same ones
you can include or exclude with @option{-t} and @option{-x}.  The particular
types printed are whatever is supported by the system.  Here are some of
the common names (this list is certainly not exhaustive):

@table @samp

@item nfs
@cindex NFS file system type
An NFS file system, i.e., one mounted over a network from another
machine.  This is the one type name which seems to be used uniformly by
all systems.

@item ext2@r{, }ext3@r{, }ext4@r{, }xfs@r{, }btrfs@dots{}
@cindex Linux file system types
@cindex local file system types
@opindex ext2 @r{file system type}
@opindex ext3 @r{file system type}
@opindex ext4 @r{file system type}
@opindex xfs @r{file system type}
@opindex btrfs @r{file system type}
A file system on a locally-mounted hard disk.  (The system might even
support more than one type here; Linux does.)

@item iso9660@r{, }cdfs
@cindex CD-ROM file system type
@cindex DVD file system type
@cindex ISO9660 file system type
@opindex iso9660 @r{file system type}
@opindex cdfs @r{file system type}
A file system on a CD or DVD drive.  HP-UX uses @samp{cdfs}, most other
systems use @samp{iso9660}.

@item ntfs@r{,}fat
@cindex NTFS file system
@cindex DOS file system
@cindex MS-DOS file system
@cindex MS-Windows file system
@opindex ntfs @r{file system file}
@opindex fat @r{file system file}
File systems used by MS-Windows / MS-DOS.

@end table

@item -x @var{fstype}
@itemx --exclude-type=@var{fstype}
@opindex -x
@opindex --exclude-type
Limit the listing to file systems not of type @var{fstype}.
Multiple file system types can be eliminated by giving multiple
@option{-x} options.  By default, no file system types are omitted.

@item -v
Ignored; for compatibility with System V versions of @command{df}.

@end table

@command{df} is installed only on systems that have usable mount tables,
so portable scripts should not rely on its existence.

@exitstatus
Failure includes the case where no output is generated, so you can
inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
@var{dir}} to test whether @var{dir} is on a file system of type
@samp{ext3} or @samp{reiserfs}.

Since the list of file systems (@var{mtab}) is needed to determine the
file system type, failure includes the cases when that list cannot
be read and one or more of the options @option{-a}, @option{-l}, @option{-t}
or @option{-x} is used together with a file name argument.


@node du invocation
@section @command{du}: Estimate file space usage

@pindex du
@cindex file space usage
@cindex disk usage for files

@command{du} reports the amount of disk space used by the set of specified files
and for each subdirectory (of directory arguments).  Synopsis:

@example
du [@var{option}]@dots{} [@var{file}]@dots{}
@end example

With no arguments, @command{du} reports the disk space for the current
directory.  Normally the disk space is printed in units of
1024 bytes, but this can be overridden (@pxref{Block size}).
Non-integer quantities are rounded up to the next higher unit.

If two or more hard links point to the same file, only one of the hard
links is counted.  The @var{file} argument order affects which links
are counted, and changing the argument order may change the numbers
and entries that @command{du} outputs.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@optNull

@item -a
@itemx --all
@opindex -a
@opindex --all
Show counts for all files, not just directories.

@item --apparent-size
@opindex --apparent-size
Print apparent sizes, rather than disk usage.  The apparent size of a
file is the number of bytes reported by @code{wc -c} on regular files,
or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
For example, a file containing the word @samp{zoo} with no newline would,
of course, have an apparent size of 3.  Such a small file may require
anywhere from 0 to 16 KiB or more of disk space, depending on
the type and configuration of the file system on which the file resides.
However, a sparse file created with this command:

@example
dd bs=1 seek=2GiB if=/dev/null of=big
@end example

@noindent
has an apparent size of 2 GiB, yet on most modern
systems, it actually uses almost no disk space.

@item -B @var{size}
@itemx --block-size=@var{size}
@opindex -B
@opindex --block-size
@cindex file sizes
Scale sizes by @var{size} before printing them (@pxref{Block size}).
For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.

@item -b
@itemx --bytes
@opindex -b
@opindex --bytes
Equivalent to @code{--apparent-size --block-size=1}.

@item -c
@itemx --total
@opindex -c
@opindex --total
@cindex grand total of disk space
Print a grand total of all arguments after all arguments have
been processed.  This can be used to find out the total disk usage of
a given set of files or directories.

@item -D
@itemx --dereference-args
@opindex -D
@opindex --dereference-args
Dereference symbolic links that are command line arguments.
Does not affect other symbolic links.  This is helpful for finding
out the disk usage of directories, such as @file{/usr/tmp}, which
are often symbolic links.

@item -d @var{depth}
@itemx --max-depth=@var{depth}
@opindex -d @var{depth}
@opindex --max-depth=@var{depth}
@cindex limiting output of @command{du}
Show the total for each directory (and file if --all) that is at
most MAX_DEPTH levels down from the root of the hierarchy.  The root
is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.

@c --files0-from=FILE
@filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}

@item -H
@opindex -H
Equivalent to @option{--dereference-args} (@option{-D}).

@optHumanReadable

@item --inodes
@opindex --inodes
@cindex inode usage, dereferencing in @command{du}
List inode usage information instead of block usage.
This option is useful for finding directories which contain many files, and
therefore eat up most of the inodes space of a file system (see @command{df},
option @option{--inodes}).
It can well be combined with the options @option{-a}, @option{-c},
@option{-h}, @option{-l}, @option{-s}, @option{-S}, @option{-t} and
@option{-x}; however, passing other options regarding the block size, for
example @option{-b}, @option{-m} and @option{--apparent-size}, is ignored.

@item -k
@opindex -k
@cindex kibibytes for file sizes
Print sizes in 1024-byte blocks, overriding the default block size
(@pxref{Block size}).
This option is equivalent to @option{--block-size=1K}.

@item -L
@itemx --dereference
@opindex -L
@opindex --dereference
@cindex symbolic links, dereferencing in @command{du}
Dereference symbolic links (show the disk space used by the file
or directory that the link points to instead of the space used by
the link).

@item -l
@itemx --count-links
@opindex -l
@opindex --count-links
@cindex hard links, counting in @command{du}
Count the size of all files, even if they have appeared already (as a
hard link).

@item -m
@opindex -m
@cindex mebibytes for file sizes
Print sizes in 1,048,576-byte blocks, overriding the default block size
(@pxref{Block size}).
This option is equivalent to @option{--block-size=1M}.

@item -P
@itemx --no-dereference
@opindex -P
@opindex --no-dereference
@cindex symbolic links, dereferencing in @command{du}
For each symbolic links encountered by @command{du},
consider the disk space used by the symbolic link.

@item -S
@itemx --separate-dirs
@opindex -S
@opindex --separate-dirs
Normally, in the output of @command{du} (when not using @option{--summarize}),
the size listed next to a directory name, @var{d}, represents the sum
of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
With @option{--separate-dirs}, the size reported for a directory name,
@var{d}, will exclude the size of any subdirectories.

@optSi

@item -s
@itemx --summarize
@opindex -s
@opindex --summarize
Display only a total for each argument.

@item -t @var{size}
@itemx --threshold=@var{size}
@opindex -t
@opindex --threshold
Exclude entries based on a given @var{size}.  The @var{size} refers to used
blocks in normal mode (@pxref{Block size}), or inodes count in conjunction
with the @option{--inodes} option.

If @var{size} is positive, then @command{du} will only print entries with a size
greater than or equal to that.

If @var{size} is negative, then @command{du} will only print entries with a size
smaller than or equal to that.

Although GNU @command{find} can be used to find files of a certain size,
@command{du}'s @option{--threshold} option can be used to also filter
directories based on a given size.

Please note that the @option{--threshold} option can be combined with the
@option{--apparent-size} option, and in this case would elide entries based on
its apparent size.

Please note that the @option{--threshold} option can be combined with the
@option{--inodes} option, and in this case would elide entries based on
its inodes count.

Here's how you would use @option{--threshold} to find directories with a size
greater than or equal to 200 megabytes:

@example
du --threshold=200MB
@end example

Here's how you would use @option{--threshold} to find directories and files -
note the @option{-a} - with an apparent size smaller than or equal to 500 bytes:

@example
du -a -t -500 --apparent-size
@end example

Here's how you would use @option{--threshold} to find directories on the root
file system with more than 20000 inodes used in the directory tree below:

@example
du --inodes -x --threshold=20000 /
@end example


@item --time
@opindex --time
@cindex last modified dates, displaying in @command{du}
Show time of the most recent modification of any file in the directory,
or any of its subdirectories.

@item --time=ctime
@itemx --time=status
@itemx --time=use
@opindex --time
@opindex ctime@r{, show the most recent}
@opindex status time@r{, show the most recent}
@opindex use time@r{, show the most recent}
Show the most recent status change time (the @samp{ctime} in the inode) of
any file in the directory, instead of the modification time.

@item --time=atime
@itemx --time=access
@opindex --time
@opindex atime@r{, show the most recent}
@opindex access time@r{, show the most recent}
Show the most recent access time (the @samp{atime} in the inode) of
any file in the directory, instead of the modification time.

@item --time-style=@var{style}
@opindex --time-style
@cindex time style
List timestamps in style @var{style}.  This option has an effect only if
the @option{--time} option is also specified.  The @var{style} should
be one of the following:

@table @samp
@item +@var{format}
@vindex LC_TIME
List timestamps using @var{format}, where @var{format} is interpreted
like the format argument of @command{date} (@pxref{date invocation}).
For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
@command{du} to list timestamps like @samp{2002-03-30 23:45:56}.  As
with @command{date}, @var{format}'s interpretation is affected by the
@env{LC_TIME} locale category.

@item full-iso
List timestamps in full using ISO 8601 date, time, and time zone
components with nanosecond precision, e.g., @samp{2002-03-30
23:45:56.477817180 -0700}.  This style is equivalent to
@samp{+%Y-%m-%d %H:%M:%S.%N %z}.

@item long-iso
List ISO 8601 date and time components with minute precision, e.g.,
@samp{2002-03-30 23:45}.  These timestamps are shorter than
@samp{full-iso} timestamps, and are usually good enough for everyday
work.  This style is equivalent to @samp{+%Y-%m-%d %H:%M}.

@item iso
List ISO 8601 dates for timestamps, e.g., @samp{2002-03-30}.
This style is equivalent to @samp{+%Y-%m-%d}.
@end table

@vindex TIME_STYLE
You can specify the default value of the @option{--time-style} option
with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
the default style is @samp{long-iso}.  For compatibility with @command{ls},
if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
the newline and any later characters are ignored; if @env{TIME_STYLE}
begins with @samp{posix-} the @samp{posix-} is ignored; and if
@env{TIME_STYLE} is @samp{locale} it is ignored.

@item -X @var{file}
@itemx --exclude-from=@var{file}
@opindex -X @var{file}
@opindex --exclude-from=@var{file}
@cindex excluding files from @command{du}
Like @option{--exclude}, except take the patterns to exclude from @var{file},
one per line.  If @var{file} is @samp{-}, take the patterns from standard
input.

@item --exclude=@var{pattern}
@opindex --exclude=@var{pattern}
@cindex excluding files from @command{du}
When recursing, skip subdirectories or files matching @var{pattern}.
For example, @code{du --exclude='*.o'} excludes files whose names
end in @samp{.o}.

@item -x
@itemx --one-file-system
@opindex -x
@opindex --one-file-system
@cindex one file system, restricting @command{du} to
Skip directories that are on different file systems from the one that
the argument being processed is on.

@end table

@cindex NFS mounts from BSD to HP-UX
On BSD systems, @command{du} reports sizes that are half the correct
values for files that are NFS-mounted from HP-UX systems.  On HP-UX
systems, it reports sizes that are twice the correct values for
files that are NFS-mounted from BSD systems.  This is due to a flaw
in HP-UX; it also affects the HP-UX @command{du} program.

@exitstatus


@node stat invocation
@section @command{stat}: Report file or file system status

@pindex stat
@cindex file status
@cindex file system status

@command{stat} displays information about the specified file(s).  Synopsis:

@example
stat [@var{option}]@dots{} [@var{file}]@dots{}
@end example

With no option, @command{stat} reports all information about the given files.
But it also can be used to report the information of the file systems the
given files are located on.  If the files are links, @command{stat} can
also give information about the files the links point to.

@mayConflictWithShellBuiltIn{stat}

@table @samp

@item -L
@itemx --dereference
@opindex -L
@opindex --dereference
@cindex symbolic links, dereferencing in @command{stat}
Change how @command{stat} treats symbolic links.
With this option, @command{stat} acts on the file referenced
by each symbolic link argument.
Without it, @command{stat} acts on any symbolic link argument directly.

@item -f
@itemx --file-system
@opindex -f
@opindex --file-system
@cindex file systems
Report information about the file systems where the given files are located
instead of information about the files themselves.
This option implies the @option{-L} option.

@item -c
@itemx --format=@var{format}
@opindex -c
@opindex --format=@var{format}
@cindex output format
Use @var{format} rather than the default format.
@var{format} is automatically newline-terminated, so
running a command like the following with two or more @var{file}
operands produces a line of output for each operand:
@example
$ stat --format=%d:%i / /usr
2050:2
2057:2
@end example

@item --printf=@var{format}
@opindex --printf=@var{format}
@cindex output format
Use @var{format} rather than the default format.
Like @option{--format}, but interpret backslash escapes,
and do not output a mandatory trailing newline.
If you want a newline, include @samp{\n} in the @var{format}.
Here's how you would use @option{--printf} to print the device
and inode numbers of @file{/} and @file{/usr}:
@example
$ stat --printf='%d:%i\n' / /usr
2050:2
2057:2
@end example

@item -t
@itemx --terse
@opindex -t
@opindex --terse
@cindex terse output
Print the information in terse form, suitable for parsing by other programs.

The output of the following commands are identical and the @option{--format}
also identifies the items printed (in fuller form) in the default format.
Note the format string would include another @samp{%C} at the end with an
active SELinux security context.
@example
$ stat --format="%n %s %b %f %u %g %D %i %h %t %T %X %Y %Z %W %o" ...
$ stat --terse ...
@end example

The same illustrating terse output in @option{--file-system} mode:
@example
$ stat -f --format="%n %i %l %t %s %S %b %f %a %c %d" ...
$ stat -f --terse ...
@end example
@end table

The valid @var{format} directives for files with @option{--format} and
@option{--printf} are:

@itemize @bullet
@item %a - Access rights in octal (note @samp{#} and @samp{0} printf flags)
@item %A - Access rights in human readable form
@item %b - Number of blocks allocated (see @samp{%B})
@item %B - The size in bytes of each block reported by @samp{%b}
@item %C - The SELinux security context of a file, if available
@item %d - Device number in decimal
@item %D - Device number in hex
@item %f - Raw mode in hex
@item %F - File type
@item %g - Group ID of owner
@item %G - Group name of owner
@item %h - Number of hard links
@item %i - Inode number
@item %m - Mount point (See note below)
@item %n - File name
@item %N - Quoted file name with dereference if symbolic link
@item %o - Optimal I/O transfer size hint
@item %s - Total size, in bytes
@item %t - Major device type in hex (see below)
@item %T - Minor device type in hex (see below)
@item %u - User ID of owner
@item %U - User name of owner
@item %w - Time of file birth, or @samp{-} if unknown
@item %W - Time of file birth as seconds since Epoch, or @samp{0}
@item %x - Time of last access
@item %X - Time of last access as seconds since Epoch
@item %y - Time of last data modification
@item %Y - Time of last data modification as seconds since Epoch
@item %z - Time of last status change
@item %Z - Time of last status change as seconds since Epoch
@end itemize

The @samp{%a} format prints the octal mode, and so it is useful
to control the zero padding of the output with the @samp{#} and @samp{0}
printf flags. For example to pad to at least 3 wide while making larger
numbers unambiguously octal, you can use @samp{%#03a}.

The @samp{%t} and @samp{%T} formats operate on the st_rdev member of
the stat(2) structure, and are only defined for character and block
special files.  On some systems or file types, st_rdev may be used to
represent other quantities.

The @samp{%W}, @samp{%X}, @samp{%Y}, and @samp{%Z} formats accept a
precision preceded by a period to specify the number of digits to
print after the decimal point.  For example, @samp{%.3X} outputs the
last access time to millisecond precision.  If a period is given but no
precision, @command{stat} uses 9 digits, so @samp{%.X} is equivalent to
@samp{%.9X}@.  When discarding excess precision, time stamps are truncated
toward minus infinity.

@example
zero pad:
  $ stat -c '[%015Y]' /usr
  [000001288929712]
space align:
  $ stat -c '[%15Y]' /usr
  [     1288929712]
  $ stat -c '[%-15Y]' /usr
  [1288929712     ]
precision:
  $ stat -c '[%.3Y]' /usr
  [1288929712.114]
  $ stat -c '[%.Y]' /usr
  [1288929712.114951834]
@end example

The mount point printed by @samp{%m} is similar to that output
by @command{df}, except that:
@itemize @bullet
@item
stat does not dereference symlinks by default
(unless @option{-L} is specified)
@item
stat does not search for specified device nodes in the
file system list, instead operating on them directly
@item
@cindex bind mount
stat outputs the alias for a bind mounted file, rather than
the initial mount point of its backing device.
One can recursively call stat until there is no change in output,
to get the current base mount point
@end itemize

When listing file system information (@option{--file-system} (@option{-f})),
you must use a different set of @var{format} directives:

@itemize @bullet
@item %a - Free blocks available to non-super-user
@item %b - Total data blocks in file system
@item %c - Total file nodes in file system
@item %d - Free file nodes in file system
@item %f - Free blocks in file system
@item %i - File System ID in hex
@item %l - Maximum length of file names
@item %n - File name
@item %s - Block size (for faster transfers)
@item %S - Fundamental block size (for block counts)
@item %t - Type in hex
@item %T - Type in human readable form
@end itemize

@vindex TZ
Time stamps are listed according to the time zone rules specified by
the @env{TZ} environment variable, or by the system default rules if
@env{TZ} is not set.  @xref{TZ Variable,, Specifying the Time Zone
with @env{TZ}, libc, The GNU C Library Reference Manual}.

@exitstatus


@node sync invocation
@section @command{sync}: Synchronize cached writes to persistent storage

@pindex sync
@cindex synchronize disk and memory
@cindex Synchronize cached writes to persistent storage

@command{sync} synchronizes in memory files or file systems to persistent
storage.  Synopsis:

@example
sync [@var{option}] [@var{file}]@dots{}
@end example

@cindex superblock, writing
@cindex inodes, written buffered
@command{sync} writes any data buffered in memory out to disk.  This can
include (but is not limited to) modified superblocks, modified inodes,
and delayed reads and writes.  This must be implemented by the kernel;
The @command{sync} program does nothing but exercise the @code{sync},
@code{syncfs}, @code{fsync}, and @code{fdatasync} system calls.

@cindex crashes and corruption
The kernel keeps data in memory to avoid doing (relatively slow) disk
reads and writes.  This improves performance, but if the computer
crashes, data may be lost or the file system corrupted as a
result.  The @command{sync} command instructs the kernel to write
data in memory to persistent storage.

If any argument is specified then only those files will be
synchronized using the fsync(2) syscall by default.

If at least one file is specified, it is possible to change the
synchronization method with the following options.  Also see
@ref{Common options}.

@table @samp
@item -d
@itemx --data
@opindex --data
Use fdatasync(2) to sync only the data for the file,
and any metadata required to maintain file system consistency.

@item -f
@itemx --file-system
@opindex --file-system
Synchronize all the I/O waiting for the file systems that contain the file,
using the syscall syncfs(2).  Note you would usually @emph{not} specify
this option if passing a device node like @samp{/dev/sda} for example,
as that would sync the containing file system rather than the referenced one.
Note also that depending on the system, passing individual device nodes or files
may have different sync characteristics than using no arguments.
I.e., arguments passed to fsync(2) may provide greater guarantees through
write barriers, than a global sync(2) used when no arguments are provided.
@end table

@exitstatus


@node truncate invocation
@section @command{truncate}: Shrink or extend the size of a file

@pindex truncate
@cindex truncating, file sizes

@command{truncate} shrinks or extends the size of each @var{file} to the
specified size.  Synopsis:

@example
truncate @var{option}@dots{} @var{file}@dots{}
@end example

@cindex files, creating
Any @var{file} that does not exist is created.

@cindex sparse files, creating
@cindex holes, creating files with
If a @var{file} is larger than the specified size, the extra data is lost.
If a @var{file} is shorter, it is extended and the extended part (or hole)
reads as zero bytes.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -c
@itemx --no-create
@opindex -c
@opindex --no-create
Do not create files that do not exist.

@item -o
@itemx --io-blocks
@opindex -o
@opindex --io-blocks
Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.

@item -r @var{rfile}
@itemx --reference=@var{rfile}
@opindex -r
@opindex --reference
Base the size of each @var{file} on the size of @var{rfile}.

@item -s @var{size}
@itemx --size=@var{size}
@opindex -s
@opindex --size
Set or adjust the size of each @var{file} according to @var{size}.
@var{size} is in bytes unless @option{--io-blocks} is specified.
@multiplierSuffixesNoBlocks{size}

@var{size} may also be prefixed by one of the following to adjust
the size of each @var{file} based on its current size:
@example
@samp{+}  => extend by
@samp{-}  => reduce by
@samp{<}  => at most
@samp{>}  => at least
@samp{/}  => round down to multiple of
@samp{%}  => round up to multiple of
@end example

@end table

@exitstatus


@node Printing text
@chapter Printing text

@cindex printing text, commands for
@cindex commands for printing text

This section describes commands that display text strings.

@menu
* echo invocation::             Print a line of text.
* printf invocation::           Format and print data.
* yes invocation::              Print a string until interrupted.
@end menu


@node echo invocation
@section @command{echo}: Print a line of text

@pindex echo
@cindex displaying text
@cindex printing text
@cindex text, displaying
@cindex arbitrary text, displaying

@command{echo} writes each given @var{string} to standard output, with a
space between each and a newline after the last one.  Synopsis:

@example
echo [@var{option}]@dots{} [@var{string}]@dots{}
@end example

@mayConflictWithShellBuiltIn{echo}

The program accepts the following options.  Also see @ref{Common options}.
Options must precede operands, and the normally-special argument
@samp{--} has no special meaning and is treated like any other
@var{string}.

@table @samp
@item -n
@opindex -n
Do not output the trailing newline.

@item -e
@opindex -e
@cindex backslash escapes
Enable interpretation of the following backslash-escaped characters in
each @var{string}:

@table @samp
@item \a
alert (bell)
@item \b
backspace
@item \c
produce no further output
@item \e
escape
@item \f
form feed
@item \n
newline
@item \r
carriage return
@item \t
horizontal tab
@item \v
vertical tab
@item \\
backslash
@item \0@var{nnn}
the eight-bit value that is the octal number @var{nnn}
(zero to three octal digits), if @var{nnn} is
a nine-bit value, the ninth bit is ignored
@item \@var{nnn}
the eight-bit value that is the octal number @var{nnn}
(one to three octal digits), if @var{nnn} is
a nine-bit value, the ninth bit is ignored
@item \x@var{hh}
the eight-bit value that is the hexadecimal number @var{hh}
(one or two hexadecimal digits)
@end table

@item -E
@opindex -E
@cindex backslash escapes
Disable interpretation of backslash escapes in each @var{string}.
This is the default.  If @option{-e} and @option{-E} are both
specified, the last one given takes effect.

@end table

@vindex POSIXLY_CORRECT
If the @env{POSIXLY_CORRECT} environment variable is set, then when
@command{echo}'s first argument is not @option{-n} it outputs
option-like arguments instead of treating them as options.  For
example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
plain @samp{hello}.

POSIX does not require support for any options, and says
that the behavior of @command{echo} is implementation-defined if any
@var{string} contains a backslash or if the first argument is
@option{-n}.  Portable programs can use the @command{printf} command
if they need to omit trailing newlines or output control characters or
backslashes.  @xref{printf invocation}.

@exitstatus


@node printf invocation
@section @command{printf}: Format and print data

@pindex printf
@command{printf} does formatted printing of text.  Synopsis:

@example
printf @var{format} [@var{argument}]@dots{}
@end example

@command{printf} prints the @var{format} string, interpreting @samp{%}
directives and @samp{\} escapes to format numeric and string arguments
in a way that is mostly similar to the C @samp{printf} function.
@xref{Output Conversion Syntax,, @command{printf} format directives,
libc, The GNU C Library Reference Manual}, for details.
The differences are listed below.

@mayConflictWithShellBuiltIn{printf}

@itemize @bullet

@item
The @var{format} argument is reused as necessary to convert all the
given @var{argument}s.  For example, the command @samp{printf %s a b}
outputs @samp{ab}.

@item
Missing @var{argument}s are treated as null strings or as zeros,
depending on whether the context expects a string or a number.  For
example, the command @samp{printf %sx%d} prints @samp{x0}.

@item
@kindex \c
An additional escape, @samp{\c}, causes @command{printf} to produce no
further output.  For example, the command @samp{printf 'A%sC\cD%sF' B
E} prints @samp{ABC}.

@item
The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
digits, as opposed to C where it can have an unlimited number of
digits.  For example, the command @samp{printf '\x07e'} prints two
bytes, whereas the C statement @samp{printf ("\x07e")} prints just
one.

@item
@kindex %b
An additional directive @samp{%b}, prints its
argument string with @samp{\} escapes interpreted in the same way as in
the @var{format} string, except that octal escapes are of the form
@samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.  If
@samp{\@var{ooo}} is nine-bit value, ignore the ninth bit.
If a precision is also given, it limits the number of bytes printed
from the converted string.

@item
@kindex %q
An additional directive @samp{%q}, prints its argument string
in a format that can be reused as input by most shells.
Non-printable characters are escaped with the POSIX proposed @samp{$''} syntax,
and shell metacharacters are quoted appropriately.
This is an equivalent format to @command{ls --quoting=shell-escape} output.

@item
Numeric arguments must be single C constants, possibly with leading
@samp{+} or @samp{-}.  For example, @samp{printf %.4d -3} outputs
@samp{-0003}.

@item
@vindex POSIXLY_CORRECT
If the leading character of a numeric argument is @samp{"} or @samp{'}
then its value is the numeric value of the immediately following
character.  Any remaining characters are silently ignored if the
@env{POSIXLY_CORRECT} environment variable is set; otherwise, a
warning is printed.  For example, @samp{printf "%d" "'a"} outputs
@samp{97} on hosts that use the ASCII character set, since
@samp{a} has the numeric value 97 in ASCII.

@end itemize

@vindex LC_NUMERIC
A floating-point argument must use a period before any fractional
digits, but is printed according to the @env{LC_NUMERIC} category of the
current locale.  For example, in a locale whose radix character is a
comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
the command @samp{printf %g 3,14} is an error.
@xref{Floating point}.

@kindex \@var{ooo}
@kindex \x@var{hh}
@command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
(if @var{ooo} is 1 to 3 octal digits) specifying a byte to print,
and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
digits) specifying a character to print.
Note however that when @samp{\@var{ooo}} specifies a number larger than 255,
@command{printf} ignores the ninth bit.
For example, @samp{printf '\400'} is equivalent to @samp{printf '\0'}.

@kindex \uhhhh
@kindex \Uhhhhhhhh
@cindex Unicode
@cindex ISO/IEC 10646
@vindex LC_CTYPE
@command{printf} interprets two character syntaxes introduced in
ISO C 99:
@samp{\u} for 16-bit Unicode (ISO/IEC 10646)
characters, specified as
four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
@command{printf} outputs the Unicode characters
according to the @env{LC_CTYPE} locale.  Unicode characters in the ranges
U+0000@dots{}U+009F, U+D800@dots{}U+DFFF cannot be specified by this syntax,
except for U+0024 ($), U+0040 (@@), and U+0060 (@`).

The processing of @samp{\u} and @samp{\U} requires a full-featured
@code{iconv} facility.  It is activated on systems with glibc 2.2 (or newer),
or when @code{libiconv} is installed prior to this package.  Otherwise
@samp{\u} and @samp{\U} will print as-is.

The only options are a lone @option{--help} or
@option{--version}.  @xref{Common options}.
Options must precede operands.

The Unicode character syntaxes are useful for writing strings in a locale
independent way.  For example, a string containing the Euro currency symbol

@example
$ env printf '\u20AC 14.95'
@end example

@noindent
will be output correctly in all locales supporting the Euro symbol
(ISO-8859-15, UTF-8, and others).  Similarly, a Chinese string

@example
$ env printf '\u4e2d\u6587'
@end example

@noindent
will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).

Note that in these examples, the @command{printf} command has been
invoked via @command{env} to ensure that we run the program found via
your shell's search path, and not a shell alias or a built-in function.

For larger strings, you don't need to look up the hexadecimal code
values of each character one by one.  ASCII characters mixed with \u
escape sequences is also known as the JAVA source file encoding.  You can
use GNU recode 3.5c (or newer) to convert strings to this encoding.  Here
is how to convert a piece of text into a shell script which will output
this text in a locale-independent way:

@smallexample
$ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
    '\u4e2d\u6587\n' > sample.txt
$ recode BIG5..JAVA < sample.txt \
    | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
    > sample.sh
@end smallexample

@exitstatus


@node yes invocation
@section @command{yes}: Print a string until interrupted

@pindex yes
@cindex repeated output of a string

@command{yes} prints the command line arguments, separated by spaces and
followed by a newline, forever until it is killed.  If no arguments are
given, it prints @samp{y} followed by a newline forever until killed.

Upon a write error, @command{yes} exits with status @samp{1}.

The only options are a lone @option{--help} or @option{--version}.
To output an argument that begins with
@samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
@xref{Common options}.


@node Conditions
@chapter Conditions

@cindex conditions
@cindex commands for exit status
@cindex exit status commands

This section describes commands that are primarily useful for their exit
status, rather than their output.  Thus, they are often used as the
condition of shell @code{if} statements, or as the last command in a
pipeline.

@menu
* false invocation::            Do nothing, unsuccessfully.
* true invocation::             Do nothing, successfully.
* test invocation::             Check file types and compare values.
* expr invocation::             Evaluate expressions.
@end menu


@node false invocation
@section @command{false}: Do nothing, unsuccessfully

@pindex false
@cindex do nothing, unsuccessfully
@cindex failure exit status
@cindex exit status of @command{false}

@command{false} does nothing except return an exit status of 1, meaning
@dfn{failure}.  It can be used as a place holder in shell scripts
where an unsuccessful command is needed.
In most modern shells, @command{false} is a built-in command, so when
you use @samp{false} in a script, you're probably using the built-in
command, not the one documented here.

@command{false} honors the @option{--help} and @option{--version} options.

This version of @command{false} is implemented as a C program, and is thus
more secure and faster than a shell script implementation, and may safely
be used as a dummy shell for the purpose of disabling accounts.

Note that @command{false} (unlike all other programs documented herein)
exits unsuccessfully, even when invoked with
@option{--help} or @option{--version}.

Portable programs should not assume that the exit status of
@command{false} is 1, as it is greater than 1 on some
non-GNU hosts.


@node true invocation
@section @command{true}: Do nothing, successfully

@pindex true
@cindex do nothing, successfully
@cindex no-op
@cindex successful exit
@cindex exit status of @command{true}

@command{true} does nothing except return an exit status of 0, meaning
@dfn{success}.  It can be used as a place holder in shell scripts
where a successful command is needed, although the shell built-in
command @code{:} (colon) may do the same thing faster.
In most modern shells, @command{true} is a built-in command, so when
you use @samp{true} in a script, you're probably using the built-in
command, not the one documented here.

@command{true} honors the @option{--help} and @option{--version} options.

Note, however, that it is possible to cause @command{true}
to exit with nonzero status: with the @option{--help} or @option{--version}
option, and with standard
output already closed or redirected to a file that evokes an I/O error.
For example, using a Bourne-compatible shell:

@example
$ ./true --version >&-
./true: write error: Bad file number
$ ./true --version > /dev/full
./true: write error: No space left on device
@end example

This version of @command{true} is implemented as a C program, and is thus
more secure and faster than a shell script implementation, and may safely
be used as a dummy shell for the purpose of disabling accounts.

@node test invocation
@section @command{test}: Check file types and compare values

@pindex test
@cindex check file types
@cindex compare values
@cindex expression evaluation

@command{test} returns a status of 0 (true) or 1 (false) depending on the
evaluation of the conditional expression @var{expr}.  Each part of the
expression must be a separate argument.

@command{test} has file status checks, string operators, and numeric
comparison operators.

@command{test} has an alternate form that uses opening and closing
square brackets instead a leading @samp{test}.  For example, instead
of @samp{test -d /}, you can write @samp{[ -d / ]}.  The square
brackets must be separate arguments; for example, @samp{[-d /]} does
not have the desired effect.  Since @samp{test @var{expr}} and @samp{[
@var{expr} ]} have the same meaning, only the former form is discussed
below.

Synopses:

@example
test @var{expression}
test
[ @var{expression} ]
[ ]
[ @var{option}
@end example

@mayConflictWithShellBuiltIn{test}

If @var{expression} is omitted, @command{test} returns false.
If @var{expression} is a single argument,
@command{test} returns false if the argument is null and true
otherwise.  The argument
can be any string, including strings like @samp{-d}, @samp{-1},
@samp{--}, @samp{--help}, and @samp{--version} that most other
programs would treat as options.  To get help and version information,
invoke the commands @samp{[ --help} and @samp{[ --version}, without
the usual closing brackets.  @xref{Common options}.

@cindex exit status of @command{test}
Exit status:

@display
0 if the expression is true,
1 if the expression is false,
2 if an error occurred.
@end display

@menu
* File type tests::             -[bcdfhLpSt]
* Access permission tests::     -[gkruwxOG]
* File characteristic tests::   -e -s -nt -ot -ef
* String tests::                -z -n = == !=
* Numeric tests::               -eq -ne -lt -le -gt -ge
* Connectives for test::        ! -a -o
@end menu


@node File type tests
@subsection File type tests

@cindex file type tests

These options test for particular types of files.  (Everything's a file,
but not all files are the same!)

@table @samp

@item -b @var{file}
@opindex -b
@cindex block special check
True if @var{file} exists and is a block special device.

@item -c @var{file}
@opindex -c
@cindex character special check
True if @var{file} exists and is a character special device.

@item -d @var{file}
@opindex -d
@cindex directory check
True if @var{file} exists and is a directory.

@item -f @var{file}
@opindex -f
@cindex regular file check
True if @var{file} exists and is a regular file.

@item -h @var{file}
@itemx -L @var{file}
@opindex -L
@opindex -h
@cindex symbolic link check
True if @var{file} exists and is a symbolic link.
Unlike all other file-related tests, this test does not dereference
@var{file} if it is a symbolic link.

@item -p @var{file}
@opindex -p
@cindex named pipe check
True if @var{file} exists and is a named pipe.

@item -S @var{file}
@opindex -S
@cindex socket check
True if @var{file} exists and is a socket.

@item -t @var{fd}
@opindex -t
@cindex terminal check
True if @var{fd} is a file descriptor that is associated with a
terminal.

@end table


@node Access permission tests
@subsection Access permission tests

@cindex access permission tests
@cindex permission tests

These options test for particular access permissions.

@table @samp

@item -g @var{file}
@opindex -g
@cindex set-group-ID check
True if @var{file} exists and has its set-group-ID bit set.

@item -k @var{file}
@opindex -k
@cindex sticky bit check
True if @var{file} exists and has its @dfn{sticky} bit set.

@item -r @var{file}
@opindex -r
@cindex readable file check
True if @var{file} exists and read permission is granted.

@item -u @var{file}
@opindex -u
@cindex set-user-ID check
True if @var{file} exists and has its set-user-ID bit set.

@item -w @var{file}
@opindex -w
@cindex writable file check
True if @var{file} exists and write permission is granted.

@item -x @var{file}
@opindex -x
@cindex executable file check
True if @var{file} exists and execute permission is granted
(or search permission, if it is a directory).

@item -O @var{file}
@opindex -O
@cindex owned by effective user ID check
True if @var{file} exists and is owned by the current effective user ID.

@item -G @var{file}
@opindex -G
@cindex owned by effective group ID check
True if @var{file} exists and is owned by the current effective group ID.

@end table

@node File characteristic tests
@subsection File characteristic tests

@cindex file characteristic tests

These options test other file characteristics.

@table @samp

@item -e @var{file}
@opindex -e
@cindex existence-of-file check
True if @var{file} exists.

@item -s @var{file}
@opindex -s
@cindex nonempty file check
True if @var{file} exists and has a size greater than zero.

@item @var{file1} -nt @var{file2}
@opindex -nt
@cindex newer-than file check
True if @var{file1} is newer (according to modification date) than
@var{file2}, or if @var{file1} exists and @var{file2} does not.

@item @var{file1} -ot @var{file2}
@opindex -ot
@cindex older-than file check
True if @var{file1} is older (according to modification date) than
@var{file2}, or if @var{file2} exists and @var{file1} does not.

@item @var{file1} -ef @var{file2}
@opindex -ef
@cindex same file check
@cindex hard link check
True if @var{file1} and @var{file2} have the same device and inode
numbers, i.e., if they are hard links to each other.

@end table


@node String tests
@subsection String tests

@cindex string tests

These options test string characteristics.  You may need to quote
@var{string} arguments for the shell.  For example:

@example
test -n "$V"
@end example

The quotes here prevent the wrong arguments from being passed to
@command{test} if @samp{$V} is empty or contains special characters.

@table @samp

@item -z @var{string}
@opindex -z
@cindex zero-length string check
True if the length of @var{string} is zero.

@item -n @var{string}
@itemx @var{string}
@opindex -n
@cindex nonzero-length string check
True if the length of @var{string} is nonzero.

@item @var{string1} = @var{string2}
@opindex =
@cindex equal string check
True if the strings are equal.

@item @var{string1} == @var{string2}
@opindex ==
@cindex equal string check
True if the strings are equal (synonym for =).

@item @var{string1} != @var{string2}
@opindex !=
@cindex not-equal string check
True if the strings are not equal.

@end table


@node Numeric tests
@subsection Numeric tests

@cindex numeric tests
@cindex arithmetic tests

Numeric relational operators.  The arguments must be entirely numeric
(possibly negative), or the special expression @w{@code{-l @var{string}}},
which evaluates to the length of @var{string}.

@table @samp

@item @var{arg1} -eq @var{arg2}
@itemx @var{arg1} -ne @var{arg2}
@itemx @var{arg1} -lt @var{arg2}
@itemx @var{arg1} -le @var{arg2}
@itemx @var{arg1} -gt @var{arg2}
@itemx @var{arg1} -ge @var{arg2}
@opindex -eq
@opindex -ne
@opindex -lt
@opindex -le
@opindex -gt
@opindex -ge
These arithmetic binary operators return true if @var{arg1} is equal,
not-equal, less-than, less-than-or-equal, greater-than, or
greater-than-or-equal than @var{arg2}, respectively.

@end table

For example:

@example
test -1 -gt -2 && echo yes
@result{} yes
test -l abc -gt 1 && echo yes
@result{} yes
test 0x100 -eq 1
@error{} test: integer expression expected before -eq
@end example


@node Connectives for test
@subsection Connectives for @command{test}

@cindex logical connectives
@cindex connectives, logical

Note it's preferred to use shell logical primitives
rather than these logical connectives internal to @command{test},
because an expression may become ambiguous
depending on the expansion of its parameters.

For example, this becomes ambiguous when @samp{$1}
is set to @samp{'!'} and @samp{$2} to the empty string @samp{''}:

@example
test "$1" -a "$2"
@end example

and should be written as:

@example
test "$1" && test "$2"
@end example

Note the shell logical primitives also benefit from
short circuit operation, which can be significant
for file attribute tests.

@table @samp

@item ! @var{expr}
@opindex !
True if @var{expr} is false.
@samp{!} has lower precedence than all parts of @var{expr}.
Note @samp{!} needs to be specified to the left
of a binary expression, I.e., @samp{'!' 1 -gt 2}
rather than @samp{1 '!' -gt 2}.
Also @samp{!} is often a shell special character
and is best used quoted.


@item @var{expr1} -a @var{expr2}
@opindex -a
@cindex logical and operator
@cindex and operator
True if both @var{expr1} and @var{expr2} are true.
@samp{-a} is left associative,
and has a higher precedence than @samp{-o}.

@item @var{expr1} -o @var{expr2}
@opindex -o
@cindex logical or operator
@cindex or operator
True if either @var{expr1} or @var{expr2} is true.
@samp{-o} is left associative.

@end table


@node expr invocation
@section @command{expr}: Evaluate expressions

@pindex expr
@cindex expression evaluation
@cindex evaluation of expressions

@command{expr} evaluates an expression and writes the result on standard
output.  Each token of the expression must be a separate argument.

Operands are either integers or strings.  Integers consist of one or
more decimal digits, with an optional leading @samp{-}.
@command{expr} converts
anything appearing in an operand position to an integer or a string
depending on the operation being applied to it.

Strings are not quoted for @command{expr} itself, though you may need to
quote them to protect characters with special meaning to the shell,
e.g., spaces.  However, regardless of whether it is quoted, a string
operand should not be a parenthesis or any of @command{expr}'s
operators like @code{+}, so you cannot safely pass an arbitrary string
@code{$str} to expr merely by quoting it to the shell.  One way to
work around this is to use the GNU extension @code{+},
(e.g., @code{+ "$str" = foo}); a more portable way is to use
@code{@w{" $str"}} and to adjust the rest of the expression to take
the leading space into account (e.g., @code{@w{" $str" = " foo"}}).

You should not pass a negative integer or a string with leading
@samp{-} as @command{expr}'s first argument, as it might be
misinterpreted as an option; this can be avoided by parenthesization.
Also, portable scripts should not use a string operand that happens to
take the form of an integer; this can be worked around by inserting
leading spaces as mentioned above.

@cindex parentheses for grouping
Operators may be given as infix symbols or prefix keywords.  Parentheses
may be used for grouping in the usual manner.  You must quote
parentheses and many operators to avoid the shell evaluating them,
however.

When built with support for the GNU MP library, @command{expr} uses
arbitrary-precision arithmetic; otherwise, it uses native arithmetic
types and may fail due to arithmetic overflow.

The only options are @option{--help} and @option{--version}.  @xref{Common
options}.  Options must precede operands.

@cindex exit status of @command{expr}
Exit status:

@display
0 if the expression is neither null nor 0,
1 if the expression is null or 0,
2 if the expression is invalid,
3 if an internal error occurred (e.g., arithmetic overflow).
@end display

@menu
* String expressions::          + : match substr index length
* Numeric expressions::         + - * / %
* Relations for expr::          | & < <= = == != >= >
* Examples of expr::            Examples.
@end menu


@node String expressions
@subsection String expressions

@cindex string expressions
@cindex expressions, string

@command{expr} supports pattern matching and other string operators.  These
have higher precedence than both the numeric and relational operators (in
the next sections).

@table @samp

@item @var{string} : @var{regex}
@cindex pattern matching
@cindex regular expression matching
@cindex matching patterns
Perform pattern matching.  The arguments are converted to strings and the
second is considered to be a (basic, a la GNU @code{grep}) regular
expression, with a @code{^} implicitly prepended.  The first argument is
then matched against this regular expression.

If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
@code{:} expression returns the part of @var{string} that matched the
subexpression; otherwise, it returns the number of characters matched.

If the match fails, the @code{:} operator returns the null string if
@samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.

@kindex \( @r{regexp operator}
Only the first @samp{\( @dots{} \)} pair is relevant to the return
value; additional pairs are meaningful only for grouping the regular
expression operators.

@kindex \+ @r{regexp operator}
@kindex \? @r{regexp operator}
@kindex \| @r{regexp operator}
In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
operators which respectively match one or more, zero or one, or separate
alternatives.  SunOS and other @command{expr}'s treat these as regular
characters.  (POSIX allows either behavior.)
@xref{Top, , Regular Expression Library, regex, Regex}, for details of
regular expression syntax.  Some examples are in @ref{Examples of expr}.

@item match @var{string} @var{regex}
@findex match
An alternative way to do pattern matching.  This is the same as
@w{@samp{@var{string} : @var{regex}}}.

@item substr @var{string} @var{position} @var{length}
@findex substr
Returns the substring of @var{string} beginning at @var{position}
with length at most @var{length}.  If either @var{position} or
@var{length} is negative, zero, or non-numeric, returns the null string.

@item index @var{string} @var{charset}
@findex index
Returns the first position in @var{string} where the first character in
@var{charset} was found.  If no character in @var{charset} is found in
@var{string}, return 0.

@item length @var{string}
@findex length
Returns the length of @var{string}.

@item + @var{token}
@kindex +
Interpret @var{token} as a string, even if it is a keyword like @var{match}
or an operator like @code{/}.
This makes it possible to test @code{expr length + "$x"} or
@code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
This operator is a GNU extension.  Portable shell scripts should use
@code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.

@end table

To make @command{expr} interpret keywords as strings, you must use the
@code{quote} operator.


@node Numeric expressions
@subsection Numeric expressions

@cindex numeric expressions
@cindex expressions, numeric

@command{expr} supports the usual numeric operators, in order of increasing
precedence.  These numeric operators have lower precedence than the
string operators described in the previous section, and higher precedence
than the connectives (next section).

@table @samp

@item + -
@kindex +
@kindex -
@cindex addition
@cindex subtraction
Addition and subtraction.  Both arguments are converted to integers;
an error occurs if this cannot be done.

@item * / %
@kindex *
@kindex /
@kindex %
@cindex multiplication
@cindex division
@cindex remainder
Multiplication, division, remainder.  Both arguments are converted to
integers; an error occurs if this cannot be done.

@end table


@node Relations for expr
@subsection Relations for @command{expr}

@cindex connectives, logical
@cindex logical connectives
@cindex relations, numeric or string

@command{expr} supports the usual logical connectives and relations.  These
have lower precedence than the string and numeric operators
(previous sections).  Here is the list, lowest-precedence operator first.

@table @samp

@item |
@kindex |
@cindex logical or operator
@cindex or operator
Returns its first argument if that is neither null nor zero, otherwise
its second argument if it is neither null nor zero, otherwise 0.  It
does not evaluate its second argument if its first argument is neither
null nor zero.

@item &
@kindex &
@cindex logical and operator
@cindex and operator
Return its first argument if neither argument is null or zero, otherwise
0.  It does not evaluate its second argument if its first argument is
null or zero.

@item < <= = == != >= >
@kindex <
@kindex <=
@kindex =
@kindex ==
@kindex >
@kindex >=
@cindex comparison operators
@vindex LC_COLLATE
Compare the arguments and return 1 if the relation is true, 0 otherwise.
@code{==} is a synonym for @code{=}.  @command{expr} first tries to convert
both arguments to integers and do a numeric comparison; if either
conversion fails, it does a lexicographic comparison using the character
collating sequence specified by the @env{LC_COLLATE} locale.

@end table


@node Examples of expr
@subsection Examples of using @command{expr}

@cindex examples of @command{expr}
Here are a few examples, including quoting for shell metacharacters.

To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:

@example
foo=$(expr $foo + 1)
@end example

To print the non-directory part of the file name stored in
@code{$fname}, which need not contain a @code{/}:

@example
expr $fname : '.*/\(.*\)' '|' $fname
@end example

An example showing that @code{\+} is an operator:

@example
expr aaa : 'a\+'
@result{} 3
@end example

@example
expr abc : 'a\(.\)c'
@result{} b
expr index abcdef cz
@result{} 3
expr index index a
@error{} expr: syntax error
expr index + index a
@result{} 0
@end example


@node Redirection
@chapter Redirection

@cindex redirection
@cindex commands for redirection

Unix shells commonly provide several forms of @dfn{redirection}---ways
to change the input source or output destination of a command.  But one
useful redirection is performed by a separate command, not by the shell;
it's described here.

@menu
* tee invocation::              Redirect output to multiple files or processes.
@end menu


@node tee invocation
@section @command{tee}: Redirect output to multiple files or processes

@pindex tee
@cindex pipe fitting
@cindex destinations, multiple output
@cindex read from stdin and write to stdout and files

The @command{tee} command copies standard input to standard output and also
to any files given as arguments.  This is useful when you want not only
to send some data down a pipe, but also to save a copy.  Synopsis:

@example
tee [@var{option}]@dots{} [@var{file}]@dots{}
@end example

If a file being written to does not already exist, it is created.  If a
file being written to already exists, the data it previously contained
is overwritten unless the @option{-a} option is used.

In previous versions of GNU coreutils (v5.3.0 - v8.23), a @var{file} of @samp{-}
caused @command{tee} to send another copy of input to standard output.
However, as the interleaved output was not very useful, @command{tee} now
conforms to POSIX which explicitly mandates it to treat @samp{-} as a file
with such name.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp
@item -a
@itemx --append
@opindex -a
@opindex --append
Append standard input to the given files rather than overwriting
them.

@item -i
@itemx --ignore-interrupts
@opindex -i
@opindex --ignore-interrupts
Ignore interrupt signals.

@item -p
@itemx --output-error[=@var{mode}]
@opindex -p
@opindex --output-error
Adjust the behavior with errors on the outputs,
with the long form option supporting selection
between the following @var{mode}s:

@table @samp
@item warn
Warn on error opening or writing any output, including pipes.
Writing is continued to still open files/pipes.
Exit status indicates failure if any output has an error.

@item warn-nopipe
This is the default @var{mode} when not specified,
or when the short form @option{-p} is used.
Warn on error opening or writing any output, except pipes.
Writing is continued to still open files/pipes.
Exit status indicates failure if any non pipe output had an error.

@item exit
Exit on error opening or writing any output, including pipes.

@item exit-nopipe
Exit on error opening or writing any output, except pipes.
@end table

@end table

The @command{tee} command is useful when you happen to be transferring a large
amount of data and also want to summarize that data without reading
it a second time.  For example, when you are downloading a DVD image,
you often want to verify its signature or checksum right away.
The inefficient way to do it is simply:

@example
wget http://example.com/some.iso && sha1sum some.iso
@end example

One problem with the above is that it makes you wait for the
download to complete before starting the time-consuming SHA1 computation.
Perhaps even more importantly, the above requires reading
the DVD image a second time (the first was from the network).

The efficient way to do it is to interleave the download
and SHA1 computation.  Then, you'll get the checksum for
free, because the entire process parallelizes so well:

@example
# slightly contrived, to demonstrate process substitution
wget -O - http://example.com/dvd.iso \
  | tee >(sha1sum > dvd.sha1) > dvd.iso
@end example

That makes @command{tee} write not just to the expected output file,
but also to a pipe running @command{sha1sum} and saving the final
checksum in a file named @file{dvd.sha1}.

Note, however, that this example relies on a feature of modern shells
called @dfn{process substitution}
(the @samp{>(command)} syntax, above;
@xref{Process Substitution,,Process Substitution, bash,
The Bash Reference Manual}.),
so it works with @command{zsh}, @command{bash}, and @command{ksh},
but not with @command{/bin/sh}.  So if you write code like this
in a shell script, be sure to start the script with @samp{#!/bin/bash}.

Note also that if any of the process substitutions (or piped stdout)
might exit early without consuming all the data, the @option{-p} option
is needed to allow @command{tee} to continue to process the input
to any remaining outputs.

Since the above example writes to one file and one process,
a more conventional and portable use of @command{tee} is even better:

@example
wget -O - http://example.com/dvd.iso \
  | tee dvd.iso | sha1sum > dvd.sha1
@end example

You can extend this example to make @command{tee} write to two processes,
computing MD5 and SHA1 checksums in parallel.  In this case,
process substitution is required:

@example
wget -O - http://example.com/dvd.iso \
  | tee >(sha1sum > dvd.sha1) \
        >(md5sum > dvd.md5) \
  > dvd.iso
@end example

This technique is also useful when you want to make a @emph{compressed}
copy of the contents of a pipe.
Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
For a large hierarchy, @samp{du -ak} can run for a long time,
and can easily produce terabytes of data, so you won't want to
rerun the command unnecessarily.  Nor will you want to save
the uncompressed output.

Doing it the inefficient way, you can't even start the GUI
until after you've compressed all of the @command{du} output:

@example
du -ak | gzip -9 > /tmp/du.gz
gzip -d /tmp/du.gz | xdiskusage -a
@end example

With @command{tee} and process substitution, you start the GUI
right away and eliminate the decompression completely:

@example
du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
@end example

Finally, if you regularly create more than one type of
compressed tarball at once, for example when @code{make dist} creates
both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
there may be a better way.
Typical @command{automake}-generated @file{Makefile} rules create
the two compressed tar archives with commands in sequence, like this
(slightly simplified):

@example
tardir=your-pkg-M.N
tar chof - "$tardir" | gzip  -9 -c > your-pkg-M.N.tar.gz
tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
@end example

However, if the hierarchy you are archiving and compressing is larger
than a couple megabytes, and especially if you are using a multi-processor
system with plenty of memory, then you can do much better by reading the
directory contents only once and running the compression programs in parallel:

@example
tardir=your-pkg-M.N
tar chof - "$tardir" \
  | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
  | bzip2 -9 -c > your-pkg-M.N.tar.bz2
@end example

If you want to further process the output from process substitutions,
and those processes write atomically (i.e., write less than the system's
PIPE_BUF size at a time), that's possible with a construct like:

@example
tardir=your-pkg-M.N
tar chof - "$tardir" \
  | tee >(md5sum --tag) > >(sha256sum --tag) \
  | sort | gpg --clearsign > your-pkg-M.N.tar.sig
@end example

@exitstatus


@node File name manipulation
@chapter File name manipulation

@cindex file name manipulation
@cindex manipulation of file names
@cindex commands for file name manipulation

This section describes commands that manipulate file names.

@menu
* basename invocation::         Strip directory and suffix from a file name.
* dirname invocation::          Strip last file name component.
* pathchk invocation::          Check file name validity and portability.
* mktemp invocation::           Create temporary file or directory.
* realpath invocation::         Print resolved file names.
@end menu


@node basename invocation
@section @command{basename}: Strip directory and suffix from a file name

@pindex basename
@cindex strip directory and suffix from file names
@cindex directory, stripping from file names
@cindex suffix, stripping from file names
@cindex file names, stripping directory and suffix
@cindex leading directory components, stripping

@command{basename} removes any leading directory components from
@var{name}.  Synopsis:

@example
basename @var{name} [@var{suffix}]
basename @var{option}@dots{} @var{name}@dots{}
@end example

If @var{suffix} is specified and is identical to the end of @var{name},
it is removed from @var{name} as well.  Note that since trailing slashes
are removed prior to suffix matching, @var{suffix} will do nothing if it
contains slashes.  @command{basename} prints the result on standard
output.

@c This test is used both here and in the section on dirname.
@macro basenameAndDirname
Together, @command{basename} and @command{dirname} are designed such
that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
"$(dirname "$name")"; ls "$(basename "$name")"} will, too.  This works
for everything except file names containing a trailing newline.
@end macro
@basenameAndDirname

POSIX allows the implementation to define the results if
@var{name} is empty or @samp{//}.  In the former case, GNU
@command{basename} returns the empty string.  In the latter case, the
result is @samp{//} on platforms where @var{//} is distinct from
@var{/}, and @samp{/} on platforms where there is no difference.

The program accepts the following options.  Also see @ref{Common options}.
Options must precede operands.

@table @samp

@item -a
@itemx --multiple
@opindex -a
@opindex --multiple
Support more than one argument.  Treat every argument as a @var{name}.
With this, an optional @var{suffix} must be specified using the
@option{-s} option.

@item -s @var{suffix}
@itemx --suffix=@var{suffix}
@opindex -s
@opindex --suffix
Remove a trailing @var{suffix}.
This option implies the @option{-a} option.

@optZero

@end table

@exitstatus

Examples:

@smallexample
# Output "sort".
basename /usr/bin/sort

# Output "stdio".
basename include/stdio.h .h

# Output "stdio".
basename -s .h include/stdio.h

# Output "stdio" followed by "stdlib"
basename -a -s .h include/stdio.h include/stdlib.h
@end smallexample


@node dirname invocation
@section @command{dirname}: Strip last file name component

@pindex dirname
@cindex directory components, printing
@cindex stripping non-directory suffix
@cindex non-directory suffix, stripping

@command{dirname} prints all but the final slash-delimited component
of each @var{name}.  Slashes on either side of the final component are
also removed.  If the string contains no slash, @command{dirname}
prints @samp{.} (meaning the current directory).  Synopsis:

@example
dirname [@var{option}] @var{name}@dots{}
@end example

@var{name} need not be a file name, but if it is, this operation
effectively lists the directory that contains the final component,
including the case when the final component is itself a directory.

@basenameAndDirname

POSIX allows the implementation to define the results if
@var{name} is @samp{//}.  With GNU @command{dirname}, the
result is @samp{//} on platforms where @var{//} is distinct from
@var{/}, and @samp{/} on platforms where there is no difference.

The program accepts the following option.  Also see @ref{Common options}.

@table @samp

@optZero

@end table

@exitstatus

Examples:

@smallexample
# Output "/usr/bin".
dirname /usr/bin/sort
dirname /usr/bin//.//

# Output "dir1" followed by "dir2"
dirname dir1/str dir2/str

# Output ".".
dirname stdio.h
@end smallexample


@node pathchk invocation
@section @command{pathchk}: Check file name validity and portability

@pindex pathchk
@cindex file names, checking validity and portability
@cindex valid file names, checking for
@cindex portable file names, checking for

@command{pathchk} checks validity and portability of file names.  Synopsis:

@example
pathchk [@var{option}]@dots{} @var{name}@dots{}
@end example

For each @var{name}, @command{pathchk} prints an error message if any of
these conditions is true:

@enumerate
@item
One of the existing directories in @var{name} does not have search
(execute) permission,
@item
The length of @var{name} is larger than the maximum supported by the
operating system.
@item
The length of one component of @var{name} is longer than
its file system's maximum.
@end enumerate

A nonexistent @var{name} is not an error, so long a file with that
name could be created under the above conditions.

The program accepts the following options.  Also see @ref{Common options}.
Options must precede operands.

@table @samp

@item -p
@opindex -p
Instead of performing checks based on the underlying file system,
print an error message if any of these conditions is true:

@enumerate
@item
A file name is empty.

@item
A file name contains a character outside the POSIX portable file
name character set, namely, the ASCII letters and digits, @samp{.},
@samp{_}, @samp{-}, and @samp{/}.

@item
The length of a file name or one of its components exceeds the
POSIX minimum limits for portability.
@end enumerate

@item -P
@opindex -P
Print an error message if a file name is empty, or if it contains a component
that begins with @samp{-}.

@item --portability
@opindex --portability
Print an error message if a file name is not portable to all POSIX
hosts.  This option is equivalent to @samp{-p -P}.

@end table

@cindex exit status of @command{pathchk}
Exit status:

@display
0 if all specified file names passed all checks,
1 otherwise.
@end display

@node mktemp invocation
@section @command{mktemp}: Create temporary file or directory

@pindex mktemp
@cindex file names, creating temporary
@cindex directory, creating temporary
@cindex temporary files and directories

@command{mktemp} manages the creation of temporary files and
directories.  Synopsis:

@example
mktemp [@var{option}]@dots{} [@var{template}]
@end example

Safely create a temporary file or directory based on @var{template},
and print its name.  If given, @var{template} must include at least
three consecutive @samp{X}s in the last component.  If omitted, the template
@samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
implied.  The final run of @samp{X}s in the @var{template} will be replaced
by alpha-numeric characters; thus, on a case-sensitive file system,
and with a @var{template} including a run of @var{n} instances of @samp{X},
there are @samp{62**@var{n}} potential file names.

Older scripts used to create temporary files by simply joining the
name of the program with the process id (@samp{$$}) as a suffix.
However, that naming scheme is easily predictable, and suffers from a
race condition where the attacker can create an appropriately named
symbolic link, such that when the script then opens a handle to what
it thought was an unused file, it is instead modifying an existing
file.  Using the same scheme to create a directory is slightly safer,
since the @command{mkdir} will fail if the target already exists, but
it is still inferior because it allows for denial of service attacks.
Therefore, modern scripts should use the @command{mktemp} command to
guarantee that the generated name will be unpredictable, and that
knowledge of the temporary file name implies that the file was created
by the current script and cannot be modified by other users.

When creating a file, the resulting file has read and write
permissions for the current user, but no permissions for the group or
others; these permissions are reduced if the current umask is more
restrictive.

Here are some examples (although note that if you repeat them, you
will most likely get different file names):

@itemize @bullet

@item
Create a temporary file in the current directory.
@example
$ mktemp file.XXXX
file.H47c
@end example

@item
Create a temporary file with a known suffix.
@example
$ mktemp --suffix=.txt file-XXXX
file-H08W.txt
$ mktemp file-XXXX-XXXX.txt
file-XXXX-eI9L.txt
@end example

@item
Create a secure fifo relative to the user's choice of @env{TMPDIR},
but falling back to the current directory rather than @file{/tmp}.
Note that @command{mktemp} does not create fifos, but can create a
secure directory in which the fifo can live.  Exit the shell if the
directory or fifo could not be created.
@example
$ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
$ fifo=$dir/fifo
$ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @}
@end example

@item
Create and use a temporary file if possible, but ignore failure.  The
file will reside in the directory named by @env{TMPDIR}, if specified,
or else in @file{/tmp}.
@example
$ file=$(mktemp -q) && @{
>   # Safe to use $file only within this block.  Use quotes,
>   # since $TMPDIR, and thus $file, may contain whitespace.
>   echo ... > "$file"
>   rm "$file"
> @}
@end example

@item
Act as a semi-random character generator (it is not fully random,
since it is impacted by the contents of the current directory).  To
avoid security holes, do not use the resulting names to create a file.
@example
$ mktemp -u XXX
Gb9
$ mktemp -u XXX
nzC
@end example

@end itemize

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -d
@itemx --directory
@opindex -d
@opindex --directory
Create a directory rather than a file.  The directory will have read,
write, and search permissions for the current user, but no permissions
for the group or others; these permissions are reduced if the current
umask is more restrictive.

@item -q
@itemx --quiet
@opindex -q
@opindex --quiet
Suppress diagnostics about failure to create a file or directory.  The
exit status will still reflect whether a file was created.

@item -u
@itemx --dry-run
@opindex -u
@opindex --dry-run
Generate a temporary name that does not name an existing file, without
changing the file system contents.  Using the output of this command
to create a new file is inherently unsafe, as there is a window of
time between generating the name and using it where another process
can create an object by the same name.

@item -p @var{dir}
@itemx --tmpdir[=@var{dir}]
@opindex -p
@opindex --tmpdir
Treat @var{template} relative to the directory @var{dir}.  If
@var{dir} is not specified (only possible with the long option
@option{--tmpdir}) or is the empty string, use the value of
@env{TMPDIR} if available, otherwise use @samp{/tmp}.  If this is
specified, @var{template} must not be absolute.  However,
@var{template} can still contain slashes, although intermediate
directories must already exist.

@item --suffix=@var{suffix}
@opindex --suffix
Append @var{suffix} to the @var{template}.  @var{suffix} must not
contain slash.  If @option{--suffix} is specified, @var{template} must
end in @samp{X}; if it is not specified, then an appropriate
@option{--suffix} is inferred by finding the last @samp{X} in
@var{template}.  This option exists for use with the default
@var{template} and for the creation of a @var{suffix} that starts with
@samp{X}.

@item -t
@opindex -t
Treat @var{template} as a single file relative to the value of
@env{TMPDIR} if available, or to the directory specified by
@option{-p}, otherwise to @samp{/tmp}.  @var{template} must not
contain slashes.  This option is deprecated; the use of @option{-p}
without @option{-t} offers better defaults (by favoring the command
line over @env{TMPDIR}) and more flexibility (by allowing intermediate
directories).

@end table

@cindex exit status of @command{mktemp}
Exit status:

@display
0 if the file was created,
1 otherwise.
@end display


@node realpath invocation
@section @command{realpath}: Print the resolved file name.

@pindex realpath
@cindex file names, canonicalization
@cindex symlinks, resolution
@cindex canonical file name
@cindex canonicalize a file name
@pindex realpath
@findex realpath

@command{realpath} expands all symbolic links and resolves references to
@samp{/./}, @samp{/../} and extra @samp{/} characters.  By default,
all but the last component of the specified files must exist.  Synopsis:

@example
realpath [@var{option}]@dots{} @var{file}@dots{}
@end example

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -e
@itemx --canonicalize-existing
@opindex -e
@opindex --canonicalize-existing
Ensure that all components of the specified file names exist.
If any component is missing or unavailable, @command{realpath} will output
a diagnostic unless the @option{-q} option is specified, and exit with a
nonzero exit code.  A trailing slash requires that the name resolve to a
directory.

@item -m
@itemx --canonicalize-missing
@opindex -m
@opindex --canonicalize-missing
If any component of a specified file name is missing or unavailable,
treat it as a directory.

@item -L
@itemx --logical
@opindex -L
@opindex --logical
Symbolic links are resolved in the specified file names,
but they are resolved after any subsequent @samp{..} components are processed.

@item -P
@itemx --physical
@opindex -P
@opindex --physical
Symbolic links are resolved in the specified file names,
and they are resolved before any subsequent @samp{..} components are processed.
This is the default mode of operation.

@item -q
@itemx --quiet
@opindex -q
@opindex --quiet
Suppress diagnostic messages for specified file names.

@item --relative-to=@var{file}
@opindex --relative-to
@cindex relpath
Print the resolved file names relative to the specified file.
Note this option honors the @option{-m} and @option{-e} options
pertaining to file existence.

@item --relative-base=@var{base}
@opindex --relative-base
This option is valid when used with @option{--relative-to}, and will restrict
the output of @option{--relative-to} so that relative names are output,
only when @var{file}s are descendants of @var{base}.  Otherwise output the
absolute file name.  If @option{--relative-to} was not specified, then
the descendants of @var{base} are printed relative to @var{base}.  If
@option{--relative-to} is specified, then that directory must be a
descendant of @var{base} for this option to have an effect.
Note: this option honors the @option{-m} and @option{-e}
options pertaining to file existence.  For example:

@example
realpath --relative-to=/usr /tmp /usr/bin
@result{} ../tmp
@result{} bin
realpath --relative-base=/usr /tmp /usr/bin
@result{} /tmp
@result{} bin
@end example

@item -s
@itemx --strip
@itemx --no-symlinks
@opindex -s
@opindex --strip
@opindex --no-symlinks
Do not resolve symbolic links.  Only resolve references to
@samp{/./}, @samp{/../} and remove extra @samp{/} characters.
When combined with the @option{-m} option, realpath operates
only on the file name, and does not touch any actual file.

@optZero

@end table

@cindex exit status of @command{realpath}
Exit status:

@display
0 if all file names were printed without issue.
1 otherwise.
@end display


@node Working context
@chapter Working context

@cindex working context
@cindex commands for printing the working context

This section describes commands that display or alter the context in
which you are working: the current directory, the terminal settings, and
so forth.  See also the user-related commands in the next section.

@menu
* pwd invocation::              Print working directory.
* stty invocation::             Print or change terminal characteristics.
* printenv invocation::         Print environment variables.
* tty invocation::              Print file name of terminal on standard input.
@end menu


@node pwd invocation
@section @command{pwd}: Print working directory

@pindex pwd
@cindex print name of current directory
@cindex current working directory, printing
@cindex working directory, printing


@command{pwd} prints the name of the current directory.  Synopsis:

@example
pwd [@var{option}]@dots{}
@end example

The program accepts the following options.  Also see @ref{Common options}.

@table @samp
@item -L
@itemx --logical
@opindex -L
@opindex --logical
If the contents of the environment variable @env{PWD} provide an
absolute name of the current directory with no @samp{.} or @samp{..}
components, but possibly with symbolic links, then output those
contents.  Otherwise, fall back to default @option{-P} handling.

@item -P
@itemx --physical
@opindex -P
@opindex --physical
Print a fully resolved name for the current directory.  That is, all
components of the printed name will be actual directory names---none
will be symbolic links.
@end table

@cindex symbolic links and @command{pwd}
If @option{-L} and @option{-P} are both given, the last one takes
precedence.  If neither option is given, then this implementation uses
@option{-P} as the default unless the @env{POSIXLY_CORRECT}
environment variable is set.

@mayConflictWithShellBuiltIn{pwd}

@exitstatus


@node stty invocation
@section @command{stty}: Print or change terminal characteristics

@pindex stty
@cindex change or print terminal settings
@cindex terminal settings
@cindex line settings of terminal

@command{stty} prints or changes terminal characteristics, such as baud rate.
Synopses:

@example
stty [@var{option}] [@var{setting}]@dots{}
stty [@var{option}]
@end example

If given no line settings, @command{stty} prints the baud rate, line
discipline number (on systems that support it), and line settings
that have been changed from the values set by @samp{stty sane}.
By default, mode reading and setting are performed on the tty line
connected to standard input, although this can be modified by the
@option{--file} option.

@command{stty} accepts many non-option arguments that change aspects of
the terminal line operation, as described below.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp
@item -a
@itemx --all
@opindex -a
@opindex --all
Print all current settings in human-readable form.  This option may not
be used in combination with any line settings.

@item -F @var{device}
@itemx --file=@var{device}
@opindex -F
@opindex --file
Set the line opened by the file name specified in @var{device} instead of
the tty line connected to standard input.  This option is necessary
because opening a POSIX tty requires use of the
@code{O_NONDELAY} flag to prevent a POSIX tty from blocking
until the carrier detect line is high if
the @code{clocal} flag is not set.  Hence, it is not always possible
to allow the shell to open the device in the traditional manner.

@item -g
@itemx --save
@opindex -g
@opindex --save
@cindex machine-readable @command{stty} output
Print all current settings in a form that can be used as an argument to
another @command{stty} command to restore the current settings.  This option
may not be used in combination with any line settings.

@end table

Many settings can be turned off by preceding them with a @samp{-}.
Such arguments are marked below with ``May be negated'' in their
description.  The descriptions themselves refer to the positive
case, that is, when @emph{not} negated (unless stated otherwise,
of course).

Some settings are not available on all POSIX systems, since they use
extensions.  Such arguments are marked below with
``Non-POSIX'' in their description.  On non-POSIX
systems, those or other settings also may not
be available, but it's not feasible to document all the variations: just
try it and see.

@command{stty} is installed only on platforms with the POSIX terminal
interface, so portable scripts should not rely on its existence on
non-POSIX platforms.

@exitstatus

@menu
* Control::                     Control settings
* Input::                       Input settings
* Output::                      Output settings
* Local::                       Local settings
* Combination::                 Combination settings
* Characters::                  Special characters
* Special::                     Special settings
@end menu


@node Control
@subsection Control settings

@cindex control settings
Control settings:

@table @samp
@item parenb
@opindex parenb
@cindex two-way parity
Generate parity bit in output and expect parity bit in input.
May be negated.

@item parodd
@opindex parodd
@cindex odd parity
@cindex even parity
Set odd parity (even if negated).  May be negated.

@item cmspar
@opindex cmspar
@cindex constant parity
@cindex stick parity
@cindex mark parity
@cindex space parity
Use "stick" (mark/space) parity.  If parodd is set, the parity bit is
always 1; if parodd is not set, the parity bit is always zero.
Non-POSIX@.  May be negated.

@item cs5
@itemx cs6
@itemx cs7
@itemx cs8
@opindex cs@var{n}
@cindex character size
@cindex eight-bit characters
Set character size to 5, 6, 7, or 8 bits.

@item hup
@itemx hupcl
@opindex hup[cl]
Send a hangup signal when the last process closes the tty.  May be
negated.

@item cstopb
@opindex cstopb
@cindex stop bits
Use two stop bits per character (one if negated).  May be negated.

@item cread
@opindex cread
Allow input to be received.  May be negated.

@item clocal
@opindex clocal
@cindex modem control
Disable modem control signals.  May be negated.

@item crtscts
@opindex crtscts
@cindex hardware flow control
@cindex flow control, hardware
@cindex RTS/CTS flow control
Enable RTS/CTS flow control.  Non-POSIX@.  May be negated.

@item cdtrdsr
@opindex cdtrdsr
@cindex hardware flow control
@cindex flow control, hardware
@cindex DTR/DSR flow control
Enable DTR/DSR flow control. Non-POSIX@.  May be negated.
@end table


@node Input
@subsection Input settings

@cindex input settings
These settings control operations on data received from the terminal.

@table @samp
@item ignbrk
@opindex ignbrk
@cindex breaks, ignoring
Ignore break characters.  May be negated.

@item brkint
@opindex brkint
@cindex breaks, cause interrupts
Make breaks cause an interrupt signal.  May be negated.

@item ignpar
@opindex ignpar
@cindex parity, ignoring
Ignore characters with parity errors.  May be negated.

@item parmrk
@opindex parmrk
@cindex parity errors, marking
Mark parity errors (with a 255-0-character sequence).  May be negated.

@item inpck
@opindex inpck
Enable input parity checking.  May be negated.

@item istrip
@opindex istrip
@cindex eight-bit input
Clear high (8th) bit of input characters.  May be negated.

@item inlcr
@opindex inlcr
@cindex newline, translating to return
Translate newline to carriage return.  May be negated.

@item igncr
@opindex igncr
@cindex return, ignoring
Ignore carriage return.  May be negated.

@item icrnl
@opindex icrnl
@cindex return, translating to newline
Translate carriage return to newline.  May be negated.

@item iutf8
@opindex iutf8
@cindex input encoding, UTF-8
Assume input characters are UTF-8 encoded.  May be negated.

@item ixon
@opindex ixon
@kindex C-s/C-q flow control
@cindex XON/XOFF flow control
Enable XON/XOFF flow control (that is, @kbd{Ctrl-S}/@kbd{Ctrl-Q}).  May
be negated.

@item ixoff
@itemx tandem
@opindex ixoff
@opindex tandem
@cindex software flow control
@cindex flow control, software
Enable sending of @code{stop} character when the system input buffer
is almost full, and @code{start} character when it becomes almost
empty again.  May be negated.

@item iuclc
@opindex iuclc
@cindex uppercase, translating to lowercase
Translate uppercase characters to lowercase.  Non-POSIX@.  May be
negated.  Note ilcuc is not implemented, as one would not be able to issue
almost any (lowercase) Unix command, after invoking it.

@item ixany
@opindex ixany
Allow any character to restart output (only the start character
if negated).  Non-POSIX@.  May be negated.

@item imaxbel
@opindex imaxbel
@cindex beeping at input buffer full
Enable beeping and not flushing input buffer if a character arrives
when the input buffer is full.  Non-POSIX@.  May be negated.
@end table


@node Output
@subsection Output settings

@cindex output settings
These settings control operations on data sent to the terminal.

@table @samp
@item opost
@opindex opost
Postprocess output.  May be negated.

@item olcuc
@opindex olcuc
@cindex lowercase, translating to output
Translate lowercase characters to uppercase.  Non-POSIX@.  May be
negated.  (Note ouclc is not currently implemented.)

@item ocrnl
@opindex ocrnl
@cindex return, translating to newline
Translate carriage return to newline.  Non-POSIX@.  May be negated.

@item onlcr
@opindex onlcr
@cindex newline, translating to crlf
Translate newline to carriage return-newline.  Non-POSIX@.  May be
negated.

@item onocr
@opindex onocr
Do not print carriage returns in the first column.  Non-POSIX@.
May be negated.

@item onlret
@opindex onlret
Newline performs a carriage return.  Non-POSIX@.  May be negated.

@item ofill
@opindex ofill
@cindex pad instead of timing for delaying
Use fill (padding) characters instead of timing for delays.
Non-POSIX@.
May be negated.

@item ofdel
@opindex ofdel
@cindex pad character
Use ASCII DEL characters for fill instead of
ASCII NUL characters.  Non-POSIX@.
May be negated.

@item nl1
@itemx nl0
@opindex nl@var{n}
Newline delay style.  Non-POSIX.

@item cr3
@itemx cr2
@itemx cr1
@itemx cr0
@opindex cr@var{n}
Carriage return delay style.  Non-POSIX.

@item tab3
@itemx tab2
@itemx tab1
@itemx tab0
@opindex tab@var{n}
Horizontal tab delay style.  Non-POSIX.

@item bs1
@itemx bs0
@opindex bs@var{n}
Backspace delay style.  Non-POSIX.

@item vt1
@itemx vt0
@opindex vt@var{n}
Vertical tab delay style.  Non-POSIX.

@item ff1
@itemx ff0
@opindex ff@var{n}
Form feed delay style.  Non-POSIX.
@end table


@node Local
@subsection Local settings

@cindex local settings

@table @samp
@item isig
@opindex isig
Enable @code{interrupt}, @code{quit}, and @code{suspend} special
characters.  May be negated.

@item icanon
@opindex icanon
Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
special characters.  May be negated.

@item iexten
@opindex iexten
Enable non-POSIX special characters.  May be negated.

@item echo
@opindex echo
Echo input characters.  May be negated.

@item echoe
@itemx crterase
@opindex echoe
@opindex crterase
Echo @code{erase} characters as backspace-space-backspace.  May be
negated.

@item echok
@opindex echok
@cindex newline echoing after @code{kill}
Echo a newline after a @code{kill} character.  May be negated.

@item echonl
@opindex echonl
@cindex newline, echoing
Echo newline even if not echoing other characters.  May be negated.

@item noflsh
@opindex noflsh
@cindex flushing, disabling
Disable flushing after @code{interrupt} and @code{quit} special
characters.  May be negated.

@item xcase
@opindex xcase
@cindex case translation
Enable input and output of uppercase characters by preceding their
lowercase equivalents with @samp{\}, when @code{icanon} is set.
Non-POSIX@.  May be negated.

@item tostop
@opindex tostop
@cindex background jobs, stopping at terminal write
Stop background jobs that try to write to the terminal.  Non-POSIX@.
May be negated.

@item echoprt
@itemx prterase
@opindex echoprt
@opindex prterase
Echo erased characters backward, between @samp{\} and @samp{/}.
Non-POSIX@.  May be negated.

@item echoctl
@itemx ctlecho
@opindex echoctl
@opindex ctlecho
@cindex control characters, using @samp{^@var{c}}
@cindex hat notation for control characters
Echo control characters in hat notation (@samp{^@var{c}}) instead
of literally.  Non-POSIX@.  May be negated.

@item echoke
@itemx crtkill
@opindex echoke
@opindex crtkill
Echo the @code{kill} special character by erasing each character on
the line as indicated by the @code{echoprt} and @code{echoe} settings,
instead of by the @code{echoctl} and @code{echok} settings.
Non-POSIX@.
May be negated.

@item extproc
@opindex extproc
Enable @samp{LINEMODE}, which is used to avoid echoing
each character over high latency links.  See also
@uref{ftp://ftp.rfc-editor.org/in-notes/rfc1116.txt, Internet RFC 1116}.
Non-POSIX@.
May be negated.

@item flusho
@opindex flusho
Discard output.
Note this setting is currently ignored on GNU/Linux systems.
Non-POSIX@.
May be negated.
@end table


@node Combination
@subsection Combination settings

@cindex combination settings
Combination settings:

@table @samp
@item evenp
@opindex evenp
@itemx parity
@opindex parity
Same as @code{parenb -parodd cs7}.  May be negated.  If negated, same
as @code{-parenb cs8}.

@item oddp
@opindex oddp
Same as @code{parenb parodd cs7}.  May be negated.  If negated, same
as @code{-parenb cs8}.

@item nl
@opindex nl
Same as @code{-icrnl -onlcr}.  May be negated.  If negated, same as
@code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.

@item ek
@opindex ek
Reset the @code{erase} and @code{kill} special characters to their default
values.

@item sane
@opindex sane
Same as:

@c This is too long to write inline.
@example
cread -ignbrk brkint -inlcr -igncr icrnl
icanon iexten echo echoe echok -echonl -noflsh
-ixoff -iutf8 -iuclc -ixany imaxbel -xcase -olcuc -ocrnl
opost -ofill onlcr -onocr -onlret nl0 cr0 tab0 bs0 vt0 ff0
isig -tostop -ofdel -echoprt echoctl echoke -extproc
@end example

@noindent
and also sets all special characters to their default values.

@item cooked
@opindex cooked
Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
sets the @code{eof} and @code{eol} characters to their default values
if they are the same as the @code{min} and @code{time} characters.
May be negated.  If negated, same as @code{raw}.

@item raw
@opindex raw
Same as:

@example
-ignbrk -brkint -ignpar -parmrk -inpck -istrip
-inlcr -igncr -icrnl -ixon -ixoff -icanon -opost
-isig -iuclc -ixany -imaxbel -xcase min 1 time 0
@end example

@noindent
May be negated.  If negated, same as @code{cooked}.

@item cbreak
@opindex cbreak
Same as @option{-icanon}.  May be negated.  If negated, same as
@code{icanon}.

@item pass8
@opindex pass8
@cindex eight-bit characters
Same as @code{-parenb -istrip cs8}.  May be negated.  If negated,
same as @code{parenb istrip cs7}.

@item litout
@opindex litout
Same as @option{-parenb -istrip -opost cs8}.  May be negated.
If negated, same as @code{parenb istrip opost cs7}.

@item decctlq
@opindex decctlq
Same as @option{-ixany}.  Non-POSIX@.  May be negated.

@item tabs
@opindex tabs
Same as @code{tab0}.  Non-POSIX@.  May be negated.  If negated, same
as @code{tab3}.

@item lcase
@itemx LCASE
@opindex lcase
@opindex LCASE
Same as @code{xcase iuclc olcuc}.  Non-POSIX@.  May be negated.
(Used for terminals with uppercase characters only.)

@item crt
@opindex crt
Same as @code{echoe echoctl echoke}.

@item dec
@opindex dec
Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
@end table


@node Characters
@subsection Special characters

@cindex special characters
@cindex characters, special

The special characters' default values vary from system to system.
They are set with the syntax @samp{name value}, where the names are
listed below and the value can be given either literally, in hat
notation (@samp{^@var{c}}), or as an integer which may start with
@samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
any other digit to indicate decimal.

@cindex disabling special characters
@kindex u@r{, and disabling special characters}
For GNU stty, giving a value of @code{^-} or @code{undef} disables that
special character.  (This is incompatible with Ultrix @command{stty},
which uses  a value of @samp{u} to disable a special character.  GNU
@command{stty} treats a value @samp{u} like any other, namely to set that
special character to @key{U}.)

@table @samp

@item intr
@opindex intr
Send an interrupt signal.

@item quit
@opindex quit
Send a quit signal.

@item erase
@opindex erase
Erase the last character typed.

@item kill
@opindex kill
Erase the current line.

@item eof
@opindex eof
Send an end of file (terminate the input).

@item eol
@opindex eol
End the line.

@item eol2
@opindex eol2
Alternate character to end the line.  Non-POSIX.

@item discard
@opindex discard
@opindex flush
Alternate character to toggle discarding of output.  Non-POSIX.

@item swtch
@opindex swtch
Switch to a different shell layer.  Non-POSIX.

@item status
@opindex status
Send an info signal.  Not currently supported on Linux.  Non-POSIX.

@item start
@opindex start
Restart the output after stopping it.

@item stop
@opindex stop
Stop the output.

@item susp
@opindex susp
Send a terminal stop signal.

@item dsusp
@opindex dsusp
Send a terminal stop signal after flushing the input.  Non-POSIX.

@item rprnt
@opindex rprnt
Redraw the current line.  Non-POSIX.

@item werase
@opindex werase
Erase the last word typed.  Non-POSIX.

@item lnext
@opindex lnext
Enter the next character typed literally, even if it is a special
character.  Non-POSIX.
@end table


@node Special
@subsection Special settings

@cindex special settings

@table @samp
@item min @var{n}
@opindex min
Set the minimum number of characters that will satisfy a read until
the time value has expired, when @option{-icanon} is set.

@item time @var{n}
@opindex time
Set the number of tenths of a second before reads time out if the minimum
number of characters have not been read, when @option{-icanon} is set.

@item ispeed @var{n}
@opindex ispeed
Set the input speed to @var{n}.

@item ospeed @var{n}
@opindex ospeed
Set the output speed to @var{n}.

@item rows @var{n}
@opindex rows
Tell the tty kernel driver that the terminal has @var{n} rows.
Non-POSIX.

@item cols @var{n}
@itemx columns @var{n}
@opindex cols
@opindex columns
Tell the kernel that the terminal has @var{n} columns.  Non-POSIX.

@item drain
@opindex drain
@cindex nonblocking @command{stty} setting
Apply settings after first waiting for pending output to be transmitted.
This is enabled by default for GNU @command{stty}.
It is useful to disable this option
in cases where the system may be in a state where serial transmission
is not possible.
For example, if the system has received the @samp{DC3} character
with @code{ixon} (software flow control) enabled, then @command{stty} would
block without @code{-drain} being specified.
May be negated. Non-POSIX.

@item size
@opindex size
@vindex LINES
@vindex COLUMNS
Print the number of rows and columns that the kernel thinks the
terminal has.  (Systems that don't support rows and columns in the kernel
typically use the environment variables @env{LINES} and @env{COLUMNS}
instead; however, GNU @command{stty} does not know anything about them.)
Non-POSIX.

@item line @var{n}
@opindex line
Use line discipline @var{n}.  Non-POSIX.

@item speed
@opindex speed
Print the terminal speed.

@item @var{n}
@cindex baud rate, setting
Set the input and output speeds to @var{n}.  @var{n} can be one of: 0
50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
38400 @code{exta} @code{extb}.  @code{exta} is the same as 19200;
@code{extb} is the same as 38400.  Many systems, including GNU/Linux,
support higher speeds.  The @command{stty} command includes support
for speeds of
57600,
115200,
230400,
460800,
500000,
576000,
921600,
1000000,
1152000,
1500000,
2000000,
2500000,
3000000,
3500000,
or
4000000 where the system supports these.
0 hangs up the line if @option{-clocal} is set.
@end table


@node printenv invocation
@section @command{printenv}: Print all or some environment variables

@pindex printenv
@cindex printing all or some environment variables
@cindex environment variables, printing

@command{printenv} prints environment variable values.  Synopsis:

@example
printenv [@var{option}] [@var{variable}]@dots{}
@end example

If no @var{variable}s are specified, @command{printenv} prints the value of
every environment variable.  Otherwise, it prints the value of each
@var{variable} that is set, and nothing for those that are not set.

The program accepts the following option.  Also see @ref{Common options}.

@table @samp

@optNull

@end table

@cindex exit status of @command{printenv}
Exit status:

@display
0 if all variables specified were found
1 if at least one specified variable was not found
2 if a write error occurred
@end display


@node tty invocation
@section @command{tty}: Print file name of terminal on standard input

@pindex tty
@cindex print terminal file name
@cindex terminal file name, printing

@command{tty} prints the file name of the terminal connected to its standard
input.  It prints @samp{not a tty} if standard input is not a terminal.
Synopsis:

@example
tty [@var{option}]@dots{}
@end example

The program accepts the following option.  Also see @ref{Common options}.

@table @samp

@item -s
@itemx --silent
@itemx --quiet
@opindex -s
@opindex --silent
@opindex --quiet
Print nothing; only return an exit status.

@end table

@cindex exit status of @command{tty}
Exit status:

@display
0 if standard input is a terminal
1 if standard input is not a terminal
2 if given incorrect arguments
3 if a write error occurs
@end display


@node User information
@chapter User information

@cindex user information, commands for
@cindex commands for printing user information

This section describes commands that print user-related information:
logins, groups, and so forth.

@menu
* id invocation::               Print user identity.
* logname invocation::          Print current login name.
* whoami invocation::           Print effective user ID.
* groups invocation::           Print group names a user is in.
* users invocation::            Print login names of users currently logged in.
* who invocation::              Print who is currently logged in.
@end menu


@node id invocation
@section @command{id}: Print user identity

@pindex id
@cindex real user and group IDs, printing
@cindex effective user and group IDs, printing
@cindex printing real and effective user and group IDs

@command{id} prints information about the given user, or the process
running it if no user is specified.  Synopsis:

@example
id [@var{option}]@dots{} [@var{user}]
@end example

@var{user} can be either a user ID or a name, with name look-up
taking precedence unless the ID is specified with a leading @samp{+}.
@xref{Disambiguating names and IDs}.

@vindex POSIXLY_CORRECT
By default, it prints the real user ID, real group ID, effective user ID
if different from the real user ID, effective group ID if different from
the real group ID, and supplemental group IDs.
In addition, if SELinux
is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
then print @samp{context=@var{c}}, where @var{c} is the security context.

Each of these numeric values is preceded by an identifying string and
followed by the corresponding user or group name in parentheses.

The options cause @command{id} to print only part of the above information.
Also see @ref{Common options}.

@table @samp
@item -g
@itemx --group
@opindex -g
@opindex --group
Print only the group ID.

@item -G
@itemx --groups
@opindex -G
@opindex --groups
Print only the group ID and the supplementary groups.

@item -n
@itemx --name
@opindex -n
@opindex --name
Print the user or group name instead of the ID number.  Requires
@option{-u}, @option{-g}, or @option{-G}.

@item -r
@itemx --real
@opindex -r
@opindex --real
Print the real, instead of effective, user or group ID@.  Requires
@option{-u}, @option{-g}, or @option{-G}.

@item -u
@itemx --user
@opindex -u
@opindex --user
Print only the user ID.

@item -Z
@itemx --context
@opindex -Z
@opindex --context
@cindex SELinux
@cindex security context
Print only the security context of the process, which is generally
the user's security context inherited from the parent process.
If neither SELinux or SMACK is enabled then print a warning and
set the exit status to 1.

@item -z
@itemx --zero
@opindex -z
@opindex --zero
Delimit output items with NUL characters.
This option is not permitted when using the default format.

Example:
@example
$ id -Gn --zero
users <NUL> devs <NUL>
@end example

@end table

@macro primaryAndSupplementaryGroups{cmd,arg}
Primary and supplementary groups for a process are normally inherited
from its parent and are usually unchanged since login.  This means
that if you change the group database after logging in, @command{\cmd\}
will not reflect your changes within your existing login session.
Running @command{\cmd\} with a \arg\ causes the user and group
database to be consulted afresh, and so will give a different result.
@end macro
@primaryAndSupplementaryGroups{id,user argument}

@exitstatus

@node logname invocation
@section @command{logname}: Print current login name

@pindex logname
@cindex printing user's login name
@cindex login name, printing
@cindex user name, printing

@flindex utmp
@command{logname} prints the calling user's name, as found in a
system-maintained file (often @file{/var/run/utmp} or
@file{/etc/utmp}), and exits with a status of 0.  If there is no entry
for the calling process, @command{logname} prints
an error message and exits with a status of 1.

The only options are @option{--help} and @option{--version}.  @xref{Common
options}.

@exitstatus


@node whoami invocation
@section @command{whoami}: Print effective user ID

@pindex whoami
@cindex effective user ID, printing
@cindex printing the effective user ID

@command{whoami} prints the user name associated with the current
effective user ID@.  It is equivalent to the command @samp{id -un}.

The only options are @option{--help} and @option{--version}.  @xref{Common
options}.

@exitstatus


@node groups invocation
@section @command{groups}: Print group names a user is in

@pindex groups
@cindex printing groups a user is in
@cindex supplementary groups, printing

@command{groups} prints the names of the primary and any supplementary
groups for each given @var{username}, or the current process if no names
are given.  If more than one name is given, the name of each user is
printed before
the list of that user's groups and the user name is separated from the
group list by a colon.  Synopsis:

@example
groups [@var{username}]@dots{}
@end example

The group lists are equivalent to the output of the command @samp{id -Gn}.

The only options are @option{--help} and @option{--version}.  @xref{Common
options}.

@primaryAndSupplementaryGroups{groups,list of users}

@exitstatus

@node users invocation
@section @command{users}: Print login names of users currently logged in

@pindex users
@cindex printing current usernames
@cindex usernames, printing current

@cindex login sessions, printing users with
@command{users} prints on a single line a blank-separated list of user
names of users currently logged in to the current host.  Each user name
corresponds to a login session, so if a user has more than one login
session, that user's name will appear the same number of times in the
output.  Synopsis:

@example
users [@var{file}]
@end example

@flindex utmp
@flindex wtmp
With no @var{file} argument, @command{users} extracts its information from
a system-maintained file (often @file{/var/run/utmp} or
@file{/etc/utmp}).  If a file argument is given, @command{users} uses
that file instead.  A common choice is @file{/var/log/wtmp}.

The only options are @option{--help} and @option{--version}.  @xref{Common
options}.

The @command{users} command is installed only on platforms with the
POSIX @code{<utmpx.h>} include file or equivalent, so portable scripts
should not rely on its existence on non-POSIX platforms.

@exitstatus


@node who invocation
@section @command{who}: Print who is currently logged in

@pindex who
@cindex printing current user information
@cindex information, about current users

@command{who} prints information about users who are currently logged on.
Synopsis:

@example
@command{who} [@var{option}] [@var{file}] [am i]
@end example

@cindex terminal lines, currently used
@cindex login time
@cindex remote hostname
If given no non-option arguments, @command{who} prints the following
information for each user currently logged on: login name, terminal
line, login time, and remote hostname or X display.

@flindex utmp
@flindex wtmp
If given one non-option argument, @command{who} uses that instead of
a default system-maintained file (often @file{/var/run/utmp} or
@file{/etc/utmp}) as the name of the file containing the record of
users logged on.  @file{/var/log/wtmp} is commonly given as an argument
to @command{who} to look at who has previously logged on.

@opindex am i
@opindex who am i
If given two non-option arguments, @command{who} prints only the entry
for the user running it (determined from its standard input), preceded
by the hostname.  Traditionally, the two arguments given are @samp{am
i}, as in @samp{who am i}.

@vindex TZ
Time stamps are listed according to the time zone rules specified by
the @env{TZ} environment variable, or by the system default rules if
@env{TZ} is not set.  @xref{TZ Variable,, Specifying the Time Zone
with @env{TZ}, libc, The GNU C Library Reference Manual}.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -a
@itemx --all
@opindex -a
@opindex --all
Same as @samp{-b -d --login -p -r -t -T -u}.

@item -b
@itemx --boot
@opindex -b
@opindex --boot
Print the date and time of last system boot.

@item -d
@itemx --dead
@opindex -d
@opindex --dead
Print information corresponding to dead processes.

@item -H
@itemx --heading
@opindex -H
@opindex --heading
Print a line of column headings.

@item -l
@itemx --login
@opindex -l
@opindex --login
List only the entries that correspond to processes via which the
system is waiting for a user to login.  The user name is always @samp{LOGIN}.

@item --lookup
@opindex --lookup
Attempt to canonicalize hostnames found in utmp through a DNS lookup.  This
is not the default because it can cause significant delays on systems with
automatic dial-up internet access.

@item -m
@opindex -m
Same as @samp{who am i}.

@item -p
@itemx --process
@opindex -p
@opindex --process
List active processes spawned by init.

@item -q
@itemx --count
@opindex -q
@opindex --count
Print only the login names and the number of users logged on.
Overrides all other options.

@item -r
@itemx --runlevel
@opindex -r
@opindex --runlevel
Print the current (and maybe previous) run-level of the init process.

@item -s
@opindex -s
Ignored; for compatibility with other versions of @command{who}.

@item -t
@itemx --time
@opindex -t
@opindex --time
Print last system clock change.

@item -u
@opindex -u
@cindex idle time
After the login time, print the number of hours and minutes that the
user has been idle.  @samp{.} means the user was active in the last minute.
@samp{old} means the user has been idle for more than 24 hours.

@item -w
@itemx -T
@itemx --mesg
@itemx --message
@itemx --writable
@opindex -w
@opindex -T
@opindex --mesg
@opindex --message
@opindex --writable
@cindex message status
@pindex write@r{, allowed}
After each login name print a character indicating the user's message status:

@display
@samp{+} allowing @code{write} messages
@samp{-} disallowing @code{write} messages
@samp{?} cannot find terminal device
@end display

@end table

The @command{who} command is installed only on platforms with the
POSIX @code{<utmpx.h>} include file or equivalent, so portable scripts
should not rely on its existence on non-POSIX platforms.

@exitstatus


@node System context
@chapter System context

@cindex system context
@cindex context, system
@cindex commands for system context

This section describes commands that print or change system-wide
information.

@menu
* date invocation::             Print or set system date and time.
* arch invocation::             Print machine hardware name.
* nproc invocation::            Print the number of processors.
* uname invocation::            Print system information.
* hostname invocation::         Print or set system name.
* hostid invocation::           Print numeric host identifier.
* uptime invocation::           Print system uptime and load.
@end menu

@node date invocation
@section @command{date}: Print or set system date and time

@pindex date
@cindex time, printing or setting
@cindex printing the current time

Synopses:

@example
date [@var{option}]@dots{} [+@var{format}]
date [-u|--utc|--universal] @c this avoids a newline in the output
[ mmddHHMM[[CC]yy][.SS] ]
@end example

@vindex LC_TIME
Invoking @command{date} with no @var{format} argument is equivalent to invoking
it with a default format that depends on the @env{LC_TIME} locale category.
In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.

@vindex TZ
Normally, @command{date} uses the time zone rules indicated by the
@env{TZ} environment variable, or the system default rules if @env{TZ}
is not set.  @xref{TZ Variable,, Specifying the Time Zone with
@env{TZ}, libc, The GNU C Library Reference Manual}.

@findex strftime @r{and @command{date}}
@cindex time formats
@cindex formatting times
If given an argument that starts with a @samp{+}, @command{date} prints the
current date and time (or the date and time specified by the
@option{--date} option, see below) in the format defined by that argument,
which is similar to that of the @code{strftime} function.  Except for
conversion specifiers, which start with @samp{%}, characters in the
format string are printed unchanged.  The conversion specifiers are
described below.

@exitstatus

@menu
* Time conversion specifiers::     %[HIklMNpPrRsSTXzZ]
* Date conversion specifiers::     %[aAbBcCdDeFgGhjmuUVwWxyY]
* Literal conversion specifiers::  %[%nt]
* Padding and other flags::        Pad with zeros, spaces, etc.
* Setting the time::               Changing the system clock.
* Options for date::               Instead of the current time.
@detailmenu
* Date input formats::             Specifying date strings.
@end detailmenu
* Examples of date::               Examples.
@end menu

@node Time conversion specifiers
@subsection Time conversion specifiers

@cindex time conversion specifiers
@cindex conversion specifiers, time

@command{date} conversion specifiers related to times.

@table @samp
@item %H
hour (@samp{00}@dots{}@samp{23})
@item %I
hour (@samp{01}@dots{}@samp{12})
@item %k
hour, space padded (@samp{ 0}@dots{}@samp{23}); equivalent to @samp{%_H}@.
This is a GNU extension.
@item %l
hour, space padded (@samp{ 1}@dots{}@samp{12}); equivalent to @samp{%_I}@.
This is a GNU extension.
@item %M
minute (@samp{00}@dots{}@samp{59})
@item %N
nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
This is a GNU extension.
@item %p
locale's equivalent of either @samp{AM} or @samp{PM};
blank in many locales.
Noon is treated as @samp{PM} and midnight as @samp{AM}.
@item %P
like @samp{%p}, except lower case.
This is a GNU extension.
@item %r
locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
@item %R
24-hour hour and minute.  Same as @samp{%H:%M}.
@item %s
@cindex epoch, seconds since
@cindex seconds since the epoch
@cindex beginning of time
@cindex leap seconds
seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC@.
Leap seconds are not counted unless leap second support is available.
@xref{%s-examples}, for examples.
This is a GNU extension.
@item %S
@cindex leap seconds
second (@samp{00}@dots{}@samp{60}).
This may be @samp{60} if leap seconds are supported.
@item %T
24-hour hour, minute, and second.  Same as @samp{%H:%M:%S}.
@item %X
locale's time representation (e.g., @samp{23:13:48})
@item %z
@w{RFC 2822/ISO 8601} style numeric time zone
(e.g., @samp{-0600} or @samp{+0530}), or nothing if no
time zone is determinable.  This value reflects the numeric time zone
appropriate for the current time, using the time zone rules specified
by the @env{TZ} environment variable.
The time (and optionally, the time zone rules) can be overridden
by the @option{--date} option.
@item %:z
@w{RFC 3339/ISO 8601} style numeric time zone with
@samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
zone is determinable.
This is a GNU extension.
@item %::z
Numeric time zone to the nearest second with @samp{:} (e.g.,
@samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
determinable.
This is a GNU extension.
@item %:::z
Numeric time zone with @samp{:} using the minimum necessary precision
(e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
no time zone is determinable.
This is a GNU extension.
@item %Z
alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
time zone is determinable.  See @samp{%z} for how it is determined.
@end table


@node Date conversion specifiers
@subsection Date conversion specifiers

@cindex date conversion specifiers
@cindex conversion specifiers, date

@command{date} conversion specifiers related to dates.

@table @samp
@item %a
locale's abbreviated weekday name (e.g., @samp{Sun})
@item %A
locale's full weekday name, variable length (e.g., @samp{Sunday})
@item %b
locale's abbreviated month name (e.g., @samp{Jan})
@item %B
locale's full month name, variable length (e.g., @samp{January})
@item %c
locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
@item %C
century.  This is like @samp{%Y}, except the last two digits are omitted.
For example, it is @samp{20} if @samp{%Y} is @samp{2000},
and is @samp{-0} if @samp{%Y} is @samp{-001}.
It is normally at least two characters, but it may be more.
@item %d
day of month (e.g., @samp{01})
@item %D
date; same as @samp{%m/%d/%y}
@item %e
day of month, space padded; same as @samp{%_d}
@item %F
full date in ISO 8601 format; same as @samp{%Y-%m-%d}.
This is a good choice for a date format, as it is standard and
is easy to sort in the usual case where years are in the range
0000@dots{}9999.
@item %g
year corresponding to the ISO week number, but without the century
(range @samp{00} through @samp{99}).  This has the same format and value
as @samp{%y}, except that if the ISO week number (see
@samp{%V}) belongs
to the previous or next year, that year is used instead.
@item %G
year corresponding to the ISO week number.  This has the
same format and value as @samp{%Y}, except that if the ISO
week number (see
@samp{%V}) belongs to the previous or next year, that year is used
instead.
It is normally useful only if @samp{%V} is also used;
for example, the format @samp{%G-%m-%d} is probably a mistake,
since it combines the ISO week number year with the conventional month and day.
@item %h
same as @samp{%b}
@item %j
day of year (@samp{001}@dots{}@samp{366})
@item %m
month (@samp{01}@dots{}@samp{12})
@item %u
day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
@item %U
week number of year, with Sunday as the first day of the week
(@samp{00}@dots{}@samp{53}).
Days in a new year preceding the first Sunday are in week zero.
@item %V
ISO week number, that is, the
week number of year, with Monday as the first day of the week
(@samp{01}@dots{}@samp{53}).
If the week containing January 1 has four or more days in
the new year, then it is considered week 1; otherwise, it is week 53 of
the previous year, and the next week is week 1.  (See the ISO 8601
standard.)
@item %w
day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
@item %W
week number of year, with Monday as first day of week
(@samp{00}@dots{}@samp{53}).
Days in a new year preceding the first Monday are in week zero.
@item %x
locale's date representation (e.g., @samp{12/31/99})
@item %y
last two digits of year (@samp{00}@dots{}@samp{99})
@item %Y
year.  This is normally at least four characters, but it may be more.
Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
precedes year @samp{0000}.
@end table


@node Literal conversion specifiers
@subsection Literal conversion specifiers

@cindex literal conversion specifiers
@cindex conversion specifiers, literal

@command{date} conversion specifiers that produce literal strings.

@table @samp
@item %%
a literal %
@item %n
a newline
@item %t
a horizontal tab
@end table


@node Padding and other flags
@subsection Padding and other flags

@cindex numeric field padding
@cindex padding of numeric fields
@cindex fields, padding numeric

Unless otherwise specified, @command{date} normally pads numeric fields
with zeros, so that, for
example, numeric months are always output as two digits.
Seconds since the epoch are not padded, though,
since there is no natural width for them.

As a GNU extension, @command{date} recognizes any of the
following optional flags after the @samp{%}:

@table @samp
@item -
(hyphen) Do not pad the field; useful if the output is intended for
human consumption.
@item _
(underscore) Pad with spaces; useful if you need a fixed
number of characters in the output, but zeros are too distracting.
@item 0
(zero) Pad with zeros even if the conversion specifier
would normally pad with spaces.
@item ^
Use upper case characters if possible.
@item #
Use opposite case characters if possible.
A field that is normally upper case becomes lower case, and vice versa.
@end table

@noindent
Here are some examples of padding:

@example
date +%d/%m -d "Feb 1"
@result{} 01/02
date +%-d/%-m -d "Feb 1"
@result{} 1/2
date +%_d/%_m -d "Feb 1"
@result{}  1/ 2
@end example

As a GNU extension, you can specify the field width
(after any flag, if present) as a decimal number.  If the natural size of the
output of the field has less than the specified number of characters,
the result is written right adjusted and padded to the given
size.  For example, @samp{%9B} prints the right adjusted month name in
a field of width 9.

An optional modifier can follow the optional flag and width
specification.  The modifiers are:

@table @samp
@item E
Use the locale's alternate representation for date and time.  This
modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
@samp{%y} and @samp{%Y} conversion specifiers.  In a Japanese locale, for
example, @samp{%Ex} might yield a date format based on the Japanese
Emperors' reigns.

@item O
Use the locale's alternate numeric symbols for numbers.  This modifier
applies only to numeric conversion specifiers.
@end table

If the format supports the modifier but no alternate representation
is available, it is ignored.


@node Setting the time
@subsection Setting the time

@cindex setting the time
@cindex time setting
@cindex appropriate privileges

If given an argument that does not start with @samp{+}, @command{date} sets
the system clock to the date and time specified by that argument (as
described below).  You must have appropriate privileges to set the
system clock.  Note for changes to persist across a reboot, the
hardware clock may need to be updated from the system clock, which
might not happen automatically on your system.

The argument must consist entirely of digits, which have the following
meaning:

@table @samp
@item MM
month
@item DD
day within month
@item hh
hour
@item mm
minute
@item CC
first two digits of year (optional)
@item YY
last two digits of year (optional)
@item ss
second (optional)
@end table

Note, the @option{--date} and @option{--set} options may not be used with an
argument in the above format.  The @option{--universal} option may be used
with such an argument to indicate that the specified date and time are
relative to Coordinated Universal Time rather than to the local time zone.


@node Options for date
@subsection Options for @command{date}

@cindex @command{date} options
@cindex options for @command{date}

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -d @var{datestr}
@itemx --date=@var{datestr}
@opindex -d
@opindex --date
@cindex parsing date strings
@cindex date strings, parsing
@cindex arbitrary date strings, parsing
@opindex yesterday
@opindex tomorrow
@opindex next @var{day}
@opindex last @var{day}
Display the date and time specified in @var{datestr} instead of the
current date and time.  @var{datestr} can be in almost any common
format.  It can contain month names, time zones, @samp{am} and @samp{pm},
@samp{yesterday}, etc.  For example, @option{--date="2004-02-27
14:19:13.489392193 +0530"} specifies the instant of time that is
489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
time zone that is 5 hours and 30 minutes east of UTC.@*
Note: input currently must be in locale independent format.  E.g., the
LC_TIME=C below is needed to print back the correct date in many locales:
@example
date -d "$(LC_TIME=C date)"
@end example
@xref{Date input formats}.

@item -f @var{datefile}
@itemx --file=@var{datefile}
@opindex -f
@opindex --file
Parse each line in @var{datefile} as with @option{-d} and display the
resulting date and time.  If @var{datefile} is @samp{-}, use standard
input.  This is useful when you have many dates to process, because the
system overhead of starting up the @command{date} executable many times can
be considerable.

@item -I[@var{timespec}]
@itemx --iso-8601[=@var{timespec}]
@opindex -I[@var{timespec}]
@opindex --iso-8601[=@var{timespec}]
Display the date using the ISO 8601 format, @samp{%Y-%m-%d}.

The argument @var{timespec} specifies the number of additional
terms of the time to include.  It can be one of the following:
@table @samp
@item auto
Print just the date.  This is the default if @var{timespec} is omitted.

@item hours
Append the hour of the day to the date.

@item minutes
Append the hours and minutes.

@item seconds
Append the hours, minutes and seconds.

@item ns
Append the hours, minutes, seconds and nanoseconds.
@end table

If showing any time terms, then include the time zone using the format
@samp{%:z}.
@macro dateParseNote
This format is always suitable as input
for the @option{--date} (@option{-d}) and @option{--file}
(@option{-f}) options, regardless of the current locale.
@end macro
@dateParseNote

@item -r @var{file}
@itemx --reference=@var{file}
@opindex -r
@opindex --reference
Display the date and time of the last modification of @var{file},
instead of the current date and time.

@item -R
@itemx --rfc-822
@itemx --rfc-2822
@opindex -R
@opindex --rfc-822
@opindex --rfc-2822
Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
%z}, evaluated in the C locale so abbreviations are always in English.
For example:

@example
Fri, 09 Sep 2005 13:51:39 -0700
@end example

This format conforms to
@uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
RFCs 2822} and
@uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
current and previous standards for Internet email.

@item --rfc-3339=@var{timespec}
@opindex --rfc-3339=@var{timespec}
Display the date using a format specified by
@uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
RFC 3339}.  This is a subset of the ISO 8601
format, except that it also permits applications to use a space rather
than a @samp{T} to separate dates from times.
@dateParseNote

The argument @var{timespec} specifies how much of the time to include.
It can be one of the following:

@table @samp
@item date
Print just the full-date, e.g., @samp{2005-09-14}.
This is equivalent to the format @samp{%Y-%m-%d}.

@item seconds
Print the full-date and full-time separated by a space, e.g.,
@samp{2005-09-14 00:56:06+05:30}.  The output ends with a numeric
time-offset; here the @samp{+05:30} means that local time is five
hours and thirty minutes east of UTC@.  This is equivalent to
the format @samp{%Y-%m-%d %H:%M:%S%:z}.

@item ns
Like @samp{seconds}, but also print nanoseconds, e.g.,
@samp{2005-09-14 00:56:06.998458565+05:30}.
This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.

@end table

@item -s @var{datestr}
@itemx --set=@var{datestr}
@opindex -s
@opindex --set
Set the date and time to @var{datestr}.  See @option{-d} above.
See also @ref{Setting the time}.

@item -u
@itemx --utc
@itemx --universal
@opindex -u
@opindex --utc
@opindex --universal
@cindex Coordinated Universal Time
@cindex UTC
@cindex Greenwich Mean Time
@cindex GMT
@cindex leap seconds
@vindex TZ
Use Coordinated Universal Time (UTC) by operating as if the
@env{TZ} environment variable were set to the string @samp{UTC0}.
Coordinated
Universal Time is often called ``Greenwich Mean Time'' (GMT) for
historical reasons.
Typically, systems ignore leap seconds and thus implement an
approximation to UTC rather than true UTC.
@end table


@node Examples of date
@subsection Examples of @command{date}

@cindex examples of @command{date}

Here are a few examples.  Also see the documentation for the @option{-d}
option in the previous section.

@itemize @bullet

@item
To print the date of the day before yesterday:

@example
date --date='2 days ago'
@end example

@item
To print the date of the day three months and one day hence:

@example
date --date='3 months 1 day'
@end example

@item
To print the day of year of Christmas in the current year:

@example
date --date='25 Dec' +%j
@end example

@item
To print the current full month name and the day of the month:

@example
date '+%B %d'
@end example

But this may not be what you want because for the first nine days of
the month, the @samp{%d} expands to a zero-padded two-digit field,
for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.

@item
To print a date without the leading zero for one-digit days
of the month, you can use the (GNU extension)
@samp{-} flag to suppress
the padding altogether:

@example
date -d 1may '+%B %-d
@end example

@item
To print the current date and time in the format required by many
non-GNU versions of @command{date} when setting the system clock:

@example
date +%m%d%H%M%Y.%S
@end example

@item
To set the system clock forward by two minutes:

@example
date --set='+2 minutes'
@end example

@item
To print the date in RFC 2822 format,
use @samp{date --rfc-2822}.  Here is some example output:

@example
Fri, 09 Sep 2005 13:51:39 -0700
@end example

@anchor{%s-examples}
@item
To convert a date string to the number of seconds since the epoch
(which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
the @samp{%s} format.  That can be useful in sorting and/or graphing
and/or comparing data by date.  The following command outputs the
number of the seconds since the epoch for the time two minutes after the
epoch:

@example
date --date='1970-01-01 00:02:00 +0000' +%s
120
@end example

If you do not specify time zone information in the date string,
@command{date} uses your computer's idea of the time zone when
interpreting the string.  For example, if your computer's time zone is
that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
seconds) behind UTC:

@example
# local time zone used
date --date='1970-01-01 00:02:00' +%s
18120
@end example

@item
If you're sorting or graphing dated data, your raw date values may be
represented as seconds since the epoch.  But few people can look at
the date @samp{946684800} and casually note ``Oh, that's the first second
of the year 2000 in Greenwich, England.''

@example
date --date='2000-01-01 UTC' +%s
946684800
@end example

An alternative is to use the @option{--utc} (@option{-u}) option.
Then you may omit @samp{UTC} from the date string.  Although this
produces the same result for @samp{%s} and many other format sequences,
with a time zone offset different from zero, it would give a different
result for zone-dependent formats like @samp{%z}.

@example
date -u --date=2000-01-01 +%s
946684800
@end example

To convert such an unwieldy number of seconds back to
a more readable form, use a command like this:

@smallexample
# local time zone used
date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
1999-12-31 19:00:00 -0500
@end smallexample

Or if you do not mind depending on the @samp{@@} feature present since
coreutils 5.3.0, you could shorten this to:

@smallexample
date -d @@946684800 +"%F %T %z"
1999-12-31 19:00:00 -0500
@end smallexample

Often it is better to output UTC-relative date and time:

@smallexample
date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
2000-01-01 00:00:00 +0000
@end smallexample

@item
@cindex leap seconds
Typically the seconds count omits leap seconds, but some systems are
exceptions.  Because leap seconds are not predictable, the mapping
between the seconds count and a future timestamp is not reliable on
the atypical systems that include leap seconds in their counts.

Here is how the two kinds of systems handle the leap second at
2012-06-30 23:59:60 UTC:

@example
# Typical systems ignore leap seconds:
date --date='2012-06-30 23:59:59 +0000' +%s
1341100799
date --date='2012-06-30 23:59:60 +0000' +%s
date: invalid date '2012-06-30 23:59:60 +0000'
date --date='2012-07-01 00:00:00 +0000' +%s
1341100800
@end example

@example
# Atypical systems count leap seconds:
date --date='2012-06-30 23:59:59 +0000' +%s
1341100823
date --date='2012-06-30 23:59:60 +0000' +%s
1341100824
date --date='2012-07-01 00:00:00 +0000' +%s
1341100825
@end example

@end itemize


@node arch invocation
@section @command{arch}: Print machine hardware name

@pindex arch
@cindex print machine hardware name
@cindex system information, printing

@command{arch} prints the machine hardware name,
and is equivalent to @samp{uname -m}.
Synopsis:

@example
arch [@var{option}]
@end example

The program accepts the @ref{Common options} only.

@command{arch} is not installed by default, so portable scripts should
not rely on its existence.

@exitstatus


@node nproc invocation
@section @command{nproc}: Print the number of available processors

@pindex nproc
@cindex Print the number of processors
@cindex system information, printing

Print the number of processing units available to the current process,
which may be less than the number of online processors.
If this information is not accessible, then print the number of
processors installed.  If the @env{OMP_NUM_THREADS} environment variable is
set, then it will determine the returned value.  The result is guaranteed to be
greater than zero.  Synopsis:

@example
nproc [@var{option}]
@end example

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item --all
@opindex --all
Print the number of installed processors on the system, which may
be greater than the number online or available to the current process.
The @env{OMP_NUM_THREADS} environment variable is not honored in this case.

@item --ignore=@var{number}
@opindex --ignore
If possible, exclude this @var{number} of processing units.

@end table

@exitstatus


@node uname invocation
@section @command{uname}: Print system information

@pindex uname
@cindex print system information
@cindex system information, printing

@command{uname} prints information about the machine and operating system
it is run on.  If no options are given, @command{uname} acts as if the
@option{-s} option were given.  Synopsis:

@example
uname [@var{option}]@dots{}
@end example

If multiple options or @option{-a} are given, the selected information is
printed in this order:

@example
@var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
@var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
@end example

The information may contain internal spaces, so such output cannot be
parsed reliably.  In the following example, @var{release} is
@samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:

@smallexample
uname -a
@result{} Linux dumdum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686@c
 unknown unknown GNU/Linux
@end smallexample


The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -a
@itemx --all
@opindex -a
@opindex --all
Print all of the below information, except omit the processor type
and the hardware platform name if they are unknown.

@item -i
@itemx --hardware-platform
@opindex -i
@opindex --hardware-platform
@cindex implementation, hardware
@cindex hardware platform
@cindex platform, hardware
Print the hardware platform name
(sometimes called the hardware implementation).
Print @samp{unknown} if this information is not available.
Note this is non-portable (even across GNU/Linux distributions).

@item -m
@itemx --machine
@opindex -m
@opindex --machine
@cindex machine type
@cindex hardware class
@cindex hardware type
Print the machine hardware name (sometimes called the hardware class
or hardware type).

@item -n
@itemx --nodename
@opindex -n
@opindex --nodename
@cindex hostname
@cindex node name
@cindex network node name
Print the network node hostname.

@item -p
@itemx --processor
@opindex -p
@opindex --processor
@cindex host processor type
Print the processor type (sometimes called the instruction set
architecture or ISA).
Print @samp{unknown} if this information is not available.
Note this is non-portable (even across GNU/Linux distributions).

@item -o
@itemx --operating-system
@opindex -o
@opindex --operating-system
@cindex operating system name
Print the name of the operating system.

@item -r
@itemx --kernel-release
@opindex -r
@opindex --kernel-release
@cindex kernel release
@cindex release of kernel
Print the kernel release.

@item -s
@itemx --kernel-name
@opindex -s
@opindex --kernel-name
@cindex kernel name
@cindex name of kernel
Print the kernel name.
POSIX 1003.1-2001 (@pxref{Standards conformance}) calls this
``the implementation of the operating system'', because the
POSIX specification itself has no notion of ``kernel''.
The kernel name might be the same as the operating system name printed
by the @option{-o} or @option{--operating-system} option, but it might
differ.  Some operating systems (e.g., FreeBSD, HP-UX) have the same
name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
do not.

@item -v
@itemx --kernel-version
@opindex -v
@opindex --kernel-version
@cindex kernel version
@cindex version of kernel
Print the kernel version.

@end table

@exitstatus


@node hostname invocation
@section @command{hostname}: Print or set system name

@pindex hostname
@cindex setting the hostname
@cindex printing the hostname
@cindex system name, printing
@cindex appropriate privileges

With no arguments, @command{hostname} prints the name of the current host
system.  With one argument, it sets the current host name to the
specified string.  You must have appropriate privileges to set the host
name.  Synopsis:

@example
hostname [@var{name}]
@end example

The only options are @option{--help} and @option{--version}.  @xref{Common
options}.

@command{hostname} is not installed by default, and other packages
also supply a @command{hostname} command, so portable scripts should
not rely on its existence or on the exact behavior documented above.

@exitstatus


@node hostid invocation
@section @command{hostid}: Print numeric host identifier

@pindex hostid
@cindex printing the host identifier

@command{hostid} prints the numeric identifier of the current host
in hexadecimal.  This command accepts no arguments.
The only options are @option{--help} and @option{--version}.
@xref{Common options}.

For example, here's what it prints on one system I use:

@example
$ hostid
1bac013d
@end example

On that system, the 32-bit quantity happens to be closely
related to the system's Internet address, but that isn't always
the case.

@command{hostid} is installed only on systems that have the
@code{gethostid} function, so portable scripts should not rely on its
existence.

@exitstatus

@node uptime invocation
@section @command{uptime}: Print system uptime and load

@pindex uptime
@cindex printing the system uptime and load

@command{uptime} prints the current time, the system's uptime, the
number of logged-in users and the current load average.

If an argument is specified, it is used as the file to be read
to discover how many users are logged in.  If no argument is
specified, a system default is used (@command{uptime --help} indicates
the default setting).

The only options are @option{--help} and @option{--version}.
@xref{Common options}.

For example, here's what it prints right now on one system I use:

@example
$ uptime
 14:07  up   3:35,  3 users,  load average: 1.39, 1.15, 1.04
@end example

The precise method of calculation of load average varies somewhat
between systems.  Some systems calculate it as the average number of
runnable processes over the last 1, 5 and 15 minutes, but some systems
also include processes in the uninterruptible sleep state (that is,
those processes which are waiting for disk I/O).  The Linux kernel
includes uninterruptible processes.

@command{uptime} is installed only on platforms with infrastructure
for obtaining the boot time, and other packages also supply an
@command{uptime} command, so portable scripts should not rely on its
existence or on the exact behavior documented above.

@exitstatus

@node SELinux context
@chapter SELinux context

@cindex SELinux context
@cindex SELinux, context
@cindex commands for SELinux context

This section describes commands for operations with SELinux
contexts.

@menu
* chcon invocation::            Change SELinux context of file
* runcon invocation::           Run a command in specified SELinux context
@end menu

@node chcon invocation
@section @command{chcon}: Change SELinux context of file

@pindex chcon
@cindex changing security context
@cindex change SELinux context

@command{chcon} changes the SELinux security context of the selected files.
Synopses:

@smallexample
chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}]@c
 [-t @var{type}] @var{file}@dots{}
chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
@end smallexample

Change the SELinux security context of each @var{file} to @var{context}.
With @option{--reference}, change the security context of each @var{file}
to that of @var{rfile}.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item --dereference
@opindex --dereference
Do not affect symbolic links but what they refer to; this is the default.

@item -h
@itemx --no-dereference
@opindex -h
@opindex --no-dereference
@cindex no dereference
Affect the symbolic links themselves instead of any referenced file.

@item --reference=@var{rfile}
@opindex --reference
@cindex reference file
Use @var{rfile}'s security context rather than specifying a @var{context} value.

@item -R
@itemx --recursive
@opindex -R
@opindex --recursive
Operate on files and directories recursively.

@item --preserve-root
@opindex --preserve-root
Refuse to operate recursively on the root directory, @file{/},
when used together with the @option{--recursive} option.
@xref{Treating / specially}.

@item --no-preserve-root
@opindex --no-preserve-root
Do not treat the root directory, @file{/}, specially when operating
recursively; this is the default.
@xref{Treating / specially}.

@choptH
@xref{Traversing symlinks}.

@choptL
@xref{Traversing symlinks}.

@choptP
@xref{Traversing symlinks}.

@item -v
@itemx --verbose
@opindex -v
@opindex --verbose
@cindex diagnostic
Output a diagnostic for every file processed.

@item -u @var{user}
@itemx --user=@var{user}
@opindex -u
@opindex --user
Set user @var{user} in the target security context.

@item -r @var{role}
@itemx --role=@var{role}
@opindex -r
@opindex --role
Set role @var{role} in the target security context.

@item -t @var{type}
@itemx --type=@var{type}
@opindex -t
@opindex --type
Set type @var{type} in the target security context.

@item -l @var{range}
@itemx --range=@var{range}
@opindex -l
@opindex --range
Set range @var{range} in the target security context.

@end table

@exitstatus

@node runcon invocation
@section @command{runcon}: Run a command in specified SELinux context

@pindex runcon
@cindex run with security context


@command{runcon} runs file in specified SELinux security context.

Synopses:
@smallexample
runcon @var{context} @var{command} [@var{args}]
runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}]@c
 [-l @var{range}] @var{command} [@var{args}]
@end smallexample

Run @var{command} with completely-specified @var{context}, or with
current or transitioned security context modified by one or more of @var{level},
@var{role}, @var{type} and @var{user}.

If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
is specified, the first argument is used as the complete context.
Any additional arguments after @var{command}
are interpreted as arguments to the command.

With neither @var{context} nor @var{command}, print the current
security context.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -c
@itemx --compute
@opindex -c
@opindex --compute
Compute process transition context before modifying.

@item -u @var{user}
@itemx --user=@var{user}
@opindex -u
@opindex --user
Set user @var{user} in the target security context.

@item -r @var{role}
@itemx --role=@var{role}
@opindex -r
@opindex --role
Set role @var{role} in the target security context.

@item -t @var{type}
@itemx --type=@var{type}
@opindex -t
@opindex --type
Set type @var{type} in the target security context.

@item -l @var{range}
@itemx --range=@var{range}
@opindex -l
@opindex --range
Set range @var{range} in the target security context.

@end table

@cindex exit status of @command{runcon}
Exit status:

@display
126 if @var{command} is found but cannot be invoked
127 if @command{runcon} itself fails or if @var{command} cannot be found
the exit status of @var{command} otherwise
@end display

@node Modified command invocation
@chapter Modified command invocation

@cindex modified command invocation
@cindex invocation of commands, modified
@cindex commands for invoking other commands

This section describes commands that run other commands in some context
different than the current one: a modified environment, as a different
user, etc.

@menu
* chroot invocation::           Modify the root directory.
* env invocation::              Modify environment variables.
* nice invocation::             Modify niceness.
* nohup invocation::            Immunize to hangups.
* stdbuf invocation::           Modify buffering of standard streams.
* timeout invocation::          Run with time limit.
@end menu


@node chroot invocation
@section @command{chroot}: Run a command with a different root directory

@pindex chroot
@cindex running a program in a specified root directory
@cindex root directory, running a program in a specified

@command{chroot} runs a command with a specified root directory.
On many systems, only the super-user can do this.@footnote{However,
some systems (e.g., FreeBSD) can be configured to allow certain regular
users to use the @code{chroot} system call, and hence to run this program.
Also, on Cygwin, anyone can run the @command{chroot} command, because the
underlying function is non-privileged due to lack of support in MS-Windows.
Furthermore, the @command{chroot} command avoids the @code{chroot} system call
when @var{newroot} is identical to the old @file{/} directory for consistency
with systems where this is allowed for non-privileged users.}.
Synopses:

@example
chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
chroot @var{option}
@end example

Ordinarily, file names are looked up starting at the root of the
directory structure, i.e., @file{/}.  @command{chroot} changes the root to
the directory @var{newroot} (which must exist), then changes the working
directory to @file{/}, and finally runs @var{command} with optional @var{args}.
If @var{command} is not specified, the default is the value of the @env{SHELL}
environment variable or @command{/bin/sh} if not set, invoked with the
@option{-i} option.
@var{command} must not be a special built-in utility
(@pxref{Special built-in utilities}).

The program accepts the following options.  Also see @ref{Common options}.
Options must precede operands.

@table @samp

@item --groups=@var{groups}
@opindex --groups
Use this option to override the supplementary @var{groups} to be
used by the new process.
The items in the list (names or numeric IDs) must be separated by commas.
Use @samp{--groups=''} to disable the supplementary group look-up
implicit in the @option{--userspec} option.

@item --userspec=@var{user}[:@var{group}]
@opindex --userspec
By default, @var{command} is run with the same credentials
as the invoking process.
Use this option to run it as a different @var{user} and/or with a
different primary @var{group}.
If a @var{user} is specified then the supplementary groups
are set according to the system defined list for that user,
unless overridden with the @option{--groups} option.

@item --skip-chdir
@opindex --skip-chdir
Use this option to not change the working directory to @file{/} after changing
the root directory to @var{newroot}, i.e., inside the chroot.
This option is only permitted when @var{newroot} is the old @file{/} directory,
and therefore is mostly useful together with the @option{--groups} and
@option{--userspec} options to retain the previous working directory.

@end table

The user and group name look-up performed by the @option{--userspec}
and @option{--groups} options, is done both outside and inside
the chroot, with successful look-ups inside the chroot taking precedence.
If the specified user or group items are intended to represent a numeric ID,
then a name to ID resolving step is avoided by specifying a leading @samp{+}.
@xref{Disambiguating names and IDs}.

Here are a few tips to help avoid common problems in using chroot.
To start with a simple example, make @var{command} refer to a statically
linked binary.  If you were to use a dynamically linked executable, then
you'd have to arrange to have the shared libraries in the right place under
your new root directory.

For example, if you create a statically linked @command{ls} executable,
and put it in @file{/tmp/empty}, you can run this command as root:

@example
$ chroot /tmp/empty /ls -Rl /
@end example

Then you'll see output like this:

@example
/:
total 1023
-rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
@end example

If you want to use a dynamically linked executable, say @command{bash},
then first run @samp{ldd bash} to see what shared objects it needs.
Then, in addition to copying the actual binary, also copy the listed
files to the required positions under your intended new root directory.
Finally, if the executable requires any other files (e.g., data, state,
device files), copy them into place, too.

@command{chroot} is installed only on systems that have the
@code{chroot} function, so portable scripts should not rely on its
existence.

@cindex exit status of @command{chroot}
Exit status:

@display
125 if @command{chroot} itself fails
126 if @var{command} is found but cannot be invoked
127 if @var{command} cannot be found
the exit status of @var{command} otherwise
@end display


@node env invocation
@section @command{env}: Run a command in a modified environment

@pindex env
@cindex environment, running a program in a modified
@cindex modified environment, running a program in a
@cindex running a program in a modified environment

@command{env} runs a command with a modified environment.  Synopses:

@example
env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
[@var{command} [@var{args}]@dots{}]
env
@end example

Operands of the form @samp{@var{variable}=@var{value}} set
the environment variable @var{variable} to value @var{value}.
@var{value} may be empty (@samp{@var{variable}=}).  Setting a variable
to an empty value is different from unsetting it.
These operands are evaluated left-to-right, so if two operands
mention the same variable the earlier is ignored.

Environment variable names can be empty, and can contain any
characters other than @samp{=} and ASCII NUL.
However, it is wise to limit yourself to names that
consist solely of underscores, digits, and ASCII letters,
and that begin with a non-digit, as applications like the shell do not
work well with other names.

@vindex PATH
The first operand that does not contain the character @samp{=}
specifies the program to invoke; it is
searched for according to the @env{PATH} environment variable.  Any
remaining arguments are passed as arguments to that program.
The program should not be a special built-in utility
(@pxref{Special built-in utilities}).

Modifications to @env{PATH} take effect prior to searching for
@var{command}.  Use caution when reducing @env{PATH}; behavior is
not portable when @env{PATH} is undefined or omits key directories
such as @file{/bin}.

In the rare case that a utility contains a @samp{=} in the name, the
only way to disambiguate it from a variable assignment is to use an
intermediate command for @var{command}, and pass the problematic
program name via @var{args}.  For example, if @file{./prog=} is an
executable in the current @env{PATH}:

@example
env prog= true # runs 'true', with prog= in environment
env ./prog= true # runs 'true', with ./prog= in environment
env -- prog= true # runs 'true', with prog= in environment
env sh -c '\prog= true' # runs 'prog=' with argument 'true'
env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
@end example

@cindex environment, printing

If no command name is specified following the environment
specifications, the resulting environment is printed.  This is like
specifying the @command{printenv} program.

For some examples, suppose the environment passed to @command{env}
contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
@samp{PATH=.:/gnubin:/hacks}:

@itemize @bullet

@item
Output the current environment.
@example
$ env | LC_ALL=C sort
EDITOR=emacs
LOGNAME=rms
PATH=.:/gnubin:/hacks
@end example

@item
Run @command{foo} with a reduced environment, preserving only the
original @env{PATH} to avoid problems in locating @command{foo}.
@example
env - PATH="$PATH" foo
@end example

@item
Run @command{foo} with the environment containing @samp{LOGNAME=rms},
@samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
that @command{foo} was found in the file system rather than as a shell
built-in.
@example
env foo
@end example

@item
Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
@samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
@samp{DISPLAY=gnu:0}.
@example
env DISPLAY=gnu:0 LOGNAME=foo nemacs
@end example

@item
Attempt to run the program @command{/energy/--} (as that is the only
possible path search result); if the command exists, the environment
will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
@example
env -u EDITOR PATH=/energy -- e=mc2 bar baz
@end example

@end itemize


The program accepts the following options.  Also see @ref{Common options}.
Options must precede operands.

@table @samp

@optNull

@item -u @var{name}
@itemx --unset=@var{name}
@opindex -u
@opindex --unset
Remove variable @var{name} from the environment, if it was in the
environment.

@item -
@itemx -i
@itemx --ignore-environment
@opindex -
@opindex -i
@opindex --ignore-environment
Start with an empty environment, ignoring the inherited environment.

@end table

@cindex exit status of @command{env}
Exit status:

@display
0   if no @var{command} is specified and the environment is output
125 if @command{env} itself fails
126 if @var{command} is found but cannot be invoked
127 if @var{command} cannot be found
the exit status of @var{command} otherwise
@end display


@node nice invocation
@section @command{nice}: Run a command with modified niceness

@pindex nice
@cindex niceness
@cindex scheduling, affecting
@cindex appropriate privileges

@command{nice} prints a process's @dfn{niceness}, or runs
a command with modified niceness.  @dfn{niceness} affects how
favorably the process is scheduled in the system.
Synopsis:

@example
nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
@end example

If no arguments are given, @command{nice} prints the current niceness.
Otherwise, @command{nice} runs the given @var{command} with its
niceness adjusted.  By default, its niceness is incremented by 10.

Niceness values range at least from @minus{}20 (process has high priority
and gets more resources, thus slowing down other processes) through 19
(process has lower priority and runs slowly itself, but has less impact
on the speed of other running processes).  Some systems
may have a wider range of niceness values; conversely, other systems may
enforce more restrictive limits.  An attempt to set the niceness
outside the supported range is treated as an attempt to use the
minimum or maximum supported value.

A niceness should not be confused with a scheduling priority, which
lets applications determine the order in which threads are scheduled
to run.  Unlike a priority, a niceness is merely advice to the
scheduler, which the scheduler is free to ignore.  Also, as a point of
terminology, POSIX defines the behavior of @command{nice} in
terms of a @dfn{nice value}, which is the non-negative difference
between a niceness and the minimum niceness.  Though @command{nice}
conforms to POSIX, its documentation and diagnostics use the
term ``niceness'' for compatibility with historical practice.

@var{command} must not be a special built-in utility (@pxref{Special
built-in utilities}).

@mayConflictWithShellBuiltIn{nice}

Note to change the @dfn{niceness} of an existing process,
one needs to use the @command{renice} command.

The program accepts the following option.  Also see @ref{Common options}.
Options must precede operands.

@table @samp
@item -n @var{adjustment}
@itemx --adjustment=@var{adjustment}
@opindex -n
@opindex --adjustment
Add @var{adjustment} instead of 10 to the command's niceness.  If
@var{adjustment} is negative and you lack appropriate privileges,
@command{nice} issues a warning but otherwise acts as if you specified
a zero adjustment.

For compatibility @command{nice} also supports an obsolete
option syntax @option{-@var{adjustment}}.  New scripts should use
@option{-n @var{adjustment}} instead.

@end table

@command{nice} is installed only on systems that have the POSIX
@code{setpriority} function, so portable scripts should not rely on
its existence on non-POSIX platforms.

@cindex exit status of @command{nice}
Exit status:

@display
0   if no @var{command} is specified and the niceness is output
125 if @command{nice} itself fails
126 if @var{command} is found but cannot be invoked
127 if @var{command} cannot be found
the exit status of @var{command} otherwise
@end display

It is sometimes useful to run a non-interactive program with reduced niceness.

@example
$ nice factor 4611686018427387903
@end example

Since @command{nice} prints the current niceness,
you can invoke it through itself to demonstrate how it works.

The default behavior is to increase the niceness by @samp{10}:

@example
$ nice
0
$ nice nice
10
$ nice -n 10 nice
10
@end example

The @var{adjustment} is relative to the current niceness.  In the
next example, the first @command{nice} invocation runs the second one
with niceness 10, and it in turn runs the final one with a niceness
that is 3 more:

@example
$ nice nice -n 3 nice
13
@end example

Specifying a niceness larger than the supported range
is the same as specifying the maximum supported value:

@example
$ nice -n 10000000000 nice
19
@end example

Only a privileged user may run a process with lower niceness:

@example
$ nice -n -1 nice
nice: cannot set niceness: Permission denied
0
$ sudo nice -n -1 nice
-1
@end example


@node nohup invocation
@section @command{nohup}: Run a command immune to hangups

@pindex nohup
@cindex hangups, immunity to
@cindex immunity to hangups
@cindex logging out and continuing to run

@flindex nohup.out
@command{nohup} runs the given @var{command} with hangup signals ignored,
so that the command can continue running in the background after you log
out.  Synopsis:

@example
nohup @var{command} [@var{arg}]@dots{}
@end example

If standard input is a terminal, redirect it so that terminal sessions
do not mistakenly consider the terminal to be used by the command.
Make the substitute file descriptor unreadable, so that commands that
mistakenly attempt to read from standard input can report an error.
This redirection is a GNU extension; programs intended to be portable
to non-GNU hosts can use @samp{nohup @var{command} [@var{arg}]@dots{}
0>/dev/null} instead.

@flindex nohup.out
If standard output is a terminal, the command's standard output is appended
to the file @file{nohup.out}; if that cannot be written to, it is appended
to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
command is not run.
Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
@command{nohup} is made readable and writable only to the user,
regardless of the current umask settings.

If standard error is a terminal, it is normally redirected to the same file
descriptor as the (possibly-redirected) standard output.
However, if standard output is closed, standard error terminal output
is instead appended to the file @file{nohup.out} or
@file{$HOME/nohup.out} as above.

To capture the command's output to a file other than @file{nohup.out}
you can redirect it.  For example, to capture the output of
@command{make}:

@example
nohup make > make.log
@end example

@command{nohup} does not automatically put the command it runs in the
background; you must do that explicitly, by ending the command line
with an @samp{&}.  Also, @command{nohup} does not alter the
niceness of @var{command}; use @command{nice} for that,
e.g., @samp{nohup nice @var{command}}.

@var{command} must not be a special built-in utility (@pxref{Special
built-in utilities}).

The only options are @option{--help} and @option{--version}.  @xref{Common
options}.  Options must precede operands.

@cindex exit status of @command{nohup}
Exit status:

@display
125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
126 if @var{command} is found but cannot be invoked
127 if @var{command} cannot be found
the exit status of @var{command} otherwise
@end display

If @env{POSIXLY_CORRECT} is set, internal failures give status 127
instead of 125.


@node stdbuf invocation
@section @command{stdbuf}: Run a command with modified I/O stream buffering

@pindex stdbuf
@cindex standard streams, buffering
@cindex line buffered

@command{stdbuf} allows one to modify the buffering operations of the
three standard I/O streams associated with a program.  Synopsis:

@example
stdbuf @var{option}@dots{} @var{command}
@end example

@var{command} must start with the name of a program that
@enumerate
@item
uses the ISO C @code{FILE} streams for input/output (note the
programs @command{dd} and @command{cat} don't do that),

@item
does not adjust the buffering of its standard streams (note the
program @command{tee} is not in this category).
@end enumerate

Any additional @var{arg}s are passed as additional arguments to the
@var{command}.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -i @var{mode}
@itemx --input=@var{mode}
@opindex -i
@opindex --input
Adjust the standard input stream buffering.

@item -o @var{mode}
@itemx --output=@var{mode}
@opindex -o
@opindex --output
Adjust the standard output stream buffering.

@item -e @var{mode}
@itemx --error=@var{mode}
@opindex -e
@opindex --error
Adjust the standard error stream buffering.

@end table

The @var{mode} can be specified as follows:

@table @samp

@item L
Set the stream to line buffered mode.
In this mode data is coalesced until a newline is output or
input is read from any stream attached to a terminal device.
This option is invalid with standard input.

@item 0
Disable buffering of the selected stream.
In this mode, data is output immediately and only the
amount of data requested is read from input.
Note the difference in function for input and output.
Disabling buffering for input will not influence the responsiveness
or blocking behavior of the stream input functions.
For example @code{fread} will still block until @code{EOF} or error,
even if the underlying @code{read} returns less data than requested.

@item @var{size}
Specify the size of the buffer to use in fully buffered mode.
@multiplierSuffixesNoBlocks{size}

@end table

@command{stdbuf} is installed only on platforms that use the
Executable and Linkable Format (ELF) and support the
@code{constructor} attribute, so portable scripts should not rely on
its existence.

@cindex exit status of @command{stdbuf}
Exit status:

@display
125 if @command{stdbuf} itself fails
126 if @var{command} is found but cannot be invoked
127 if @var{command} cannot be found
the exit status of @var{command} otherwise
@end display


@node timeout invocation
@section @command{timeout}: Run a command with a time limit

@pindex timeout
@cindex time limit
@cindex run commands with bounded time

@command{timeout} runs the given @var{command} and kills it if it is
still running after the specified time interval.  Synopsis:

@example
timeout [@var{option}] @var{duration} @var{command} [@var{arg}]@dots{}
@end example

@var{command} must not be a special built-in utility (@pxref{Special
built-in utilities}).

The program accepts the following options.  Also see @ref{Common options}.
Options must precede operands.

@table @samp
@item --preserve-status
@opindex --preserve-status
Return the exit status of the managed @var{command} on timeout, rather than
a specific exit status indicating a timeout.  This is useful if the
managed @var{command} supports running for an indeterminate amount of time.

@item --foreground
@opindex --foreground
Don't create a separate background program group, so that
the managed @var{command} can use the foreground TTY normally.
This is needed to support timing out commands not started
directly from an interactive shell, in two situations.
@enumerate
@item
@var{command} is interactive and needs to read from the terminal for example
@item
the user wants to support sending signals directly to @var{command}
from the terminal (like Ctrl-C for example)
@end enumerate

Note in this mode of operation, any children of @var{command}
will not be timed out.  Also SIGCONT will not be sent to @var{command},
as it's generally not needed with foreground processes, and can
cause intermittent signal delivery issues with programs that are monitors
themselves (like GDB for example).

@item -k @var{duration}
@itemx --kill-after=@var{duration}
@opindex -k
@opindex --kill-after
Ensure the monitored @var{command} is killed by also sending a @samp{KILL}
signal, after the specified @var{duration}.  Without this option, if the
selected signal proves not to be fatal, @command{timeout} does not kill
the @var{command}.

@item -s @var{signal}
@itemx --signal=@var{signal}
@opindex -s
@opindex --signal
Send this @var{signal} to @var{command} on timeout, rather than the
default @samp{TERM} signal.  @var{signal} may be a name like @samp{HUP}
or a number.  @xref{Signal specifications}.
@end table

@cindex time units
@var{duration} is a floating point number followed by an optional unit:
@display
@samp{s} for seconds (the default)
@samp{m} for minutes
@samp{h} for hours
@samp{d} for days
@end display
A duration of 0 disables the associated timeout.
Note that the actual timeout duration is dependent on system conditions,
which should be especially considered when specifying sub-second timeouts.

@cindex exit status of @command{timeout}
Exit status:

@display
124 if @var{command} times out
125 if @command{timeout} itself fails
126 if @var{command} is found but cannot be invoked
127 if @var{command} cannot be found
137 if @var{command} is sent the KILL(9) signal (128+9)
the exit status of @var{command} otherwise
@end display


@node Process control
@chapter Process control

@cindex processes, commands for controlling
@cindex commands for controlling processes

@menu
* kill invocation::             Sending a signal to processes.
@end menu


@node kill invocation
@section @command{kill}: Send a signal to processes

@pindex kill
@cindex send a signal to processes

The @command{kill} command sends a signal to processes, causing them
to terminate or otherwise act upon receiving the signal in some way.
Alternatively, it lists information about signals.  Synopses:

@example
kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
kill [-l | --list | -t | --table] [@var{signal}]@dots{}
@end example

@mayConflictWithShellBuiltIn{kill}

The first form of the @command{kill} command sends a signal to all
@var{pid} arguments.  The default signal to send if none is specified
is @samp{TERM}@.  The special signal number @samp{0} does not denote a
valid signal, but can be used to test whether the @var{pid} arguments
specify processes to which a signal could be sent.

If @var{pid} is positive, the signal is sent to the process with the
process ID @var{pid}.  If @var{pid} is zero, the signal is sent to all
processes in the process group of the current process.  If @var{pid}
is @minus{}1, the signal is sent to all processes for which the user has
permission to send a signal.  If @var{pid} is less than @minus{}1, the signal
is sent to all processes in the process group that equals the absolute
value of @var{pid}.

If @var{pid} is not positive, a system-dependent set of system
processes is excluded from the list of processes to which the signal
is sent.

If a negative @var{pid} argument is desired as the first one, it
should be preceded by @option{--}.  However, as a common extension to
POSIX, @option{--} is not required with @samp{kill
-@var{signal} -@var{pid}}.  The following commands are equivalent:

@example
kill -15 -1
kill -TERM -1
kill -s TERM -- -1
kill -- -1
@end example

The first form of the @command{kill} command succeeds if every @var{pid}
argument specifies at least one process that the signal was sent to.

The second form of the @command{kill} command lists signal information.
Either the @option{-l} or @option{--list} option, or the @option{-t}
or @option{--table} option must be specified.  Without any
@var{signal} argument, all supported signals are listed.  The output
of @option{-l} or @option{--list} is a list of the signal names, one
per line; if @var{signal} is already a name, the signal number is
printed instead.  The output of @option{-t} or @option{--table} is a
table of signal numbers, names, and descriptions.  This form of the
@command{kill} command succeeds if all @var{signal} arguments are valid
and if there is no output error.

The @command{kill} command also supports the @option{--help} and
@option{--version} options.  @xref{Common options}.

A @var{signal} may be a signal name like @samp{HUP}, or a signal
number like @samp{1}, or an exit status of a process terminated by the
signal.  A signal name can be given in canonical form or prefixed by
@samp{SIG}@.  The case of the letters is ignored, except for the
@option{-@var{signal}} option which must use upper case to avoid
ambiguity with lower case option letters.
@xref{Signal specifications}, for a list of supported
signal names and numbers.

@node Delaying
@chapter Delaying

@cindex delaying commands
@cindex commands for delaying

@c Perhaps @command{wait} or other commands should be described here also?

@menu
* sleep invocation::            Delay for a specified time.
@end menu


@node sleep invocation
@section @command{sleep}: Delay for a specified time

@pindex sleep
@cindex delay for a specified time

@command{sleep} pauses for an amount of time specified by the sum of
the values of the command line arguments.
Synopsis:

@example
sleep @var{number}[smhd]@dots{}
@end example

@cindex time units
Each argument is a number followed by an optional unit; the default
is seconds.  The units are:

@table @samp
@item s
seconds
@item m
minutes
@item h
hours
@item d
days
@end table

Historical implementations of @command{sleep} have required that
@var{number} be an integer, and only accepted a single argument
without a suffix.  However, GNU @command{sleep} accepts
arbitrary floating point numbers.  @xref{Floating point}.

The only options are @option{--help} and @option{--version}.  @xref{Common
options}.

@c sleep is a shell built-in at least with Solaris 11's /bin/sh
@mayConflictWithShellBuiltIn{sleep}

@exitstatus


@node Numeric operations
@chapter Numeric operations

@cindex numeric operations
These programs do numerically-related operations.

@menu
* factor invocation::              Show factors of numbers.
* numfmt invocation::              Reformat numbers.
* seq invocation::                 Print sequences of numbers.
@end menu


@node factor invocation
@section @command{factor}: Print prime factors

@pindex factor
@cindex prime factors

@command{factor} prints prime factors.  Synopses:

@example
factor [@var{number}]@dots{}
factor @var{option}
@end example

If no @var{number} is specified on the command line, @command{factor} reads
numbers from standard input, delimited by newlines, tabs, or spaces.

The @command{factor} command supports only a small number of options:

@table @samp
@item --help
Print a short help on standard output, then exit without further
processing.

@item --version
Print the program version on standard output, then exit without further
processing.
@end table

Factoring the product of the eighth and ninth Mersenne primes
takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.

@example
M8=$(echo 2^31-1|bc)
M9=$(echo 2^61-1|bc)
n=$(echo "$M8 * $M9" | bc)
/usr/bin/time -f %U factor $n
4951760154835678088235319297: 2147483647 2305843009213693951
0.03
@end example

Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
about 20 seconds on the same machine.

Factoring large numbers is, in general, hard.  The Pollard-Brent rho
algorithm used by @command{factor} is particularly effective for
numbers with relatively small factors.  If you wish to factor large
numbers which do not have small factors (for example, numbers which
are the product of two large primes), other methods are far better.

If @command{factor} is built without using GNU MP, only
single-precision arithmetic is available, and so large numbers
(typically @math{2^{128}} and above) will not be supported.
The single-precision code uses an algorithm which is designed
for factoring smaller numbers.

@exitstatus


@node numfmt invocation
@section @command{numfmt}: Reformat numbers

@pindex numfmt

@command{numfmt} reads numbers in various representations and reformats them
as requested.  The most common usage is converting numbers to/from @emph{human}
representation (e.g. @samp{4G} @expansion{} @samp{4,000,000,000}).

@example
numfmt [@var{option}]@dots{} [@var{number}]
@end example

@command{numfmt} converts each @var{number} on the command-line according to the
specified options (see below).  If no @var{number}s are given, it reads numbers
from standard input.  @command{numfmt} can optionally extract numbers from
specific columns, maintaining proper line padding and alignment.

@exitstatus

See @option{--invalid} for additional information regarding exit status.

@subsection General options

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item --debug
@opindex --debug
Print (to standard error) warning messages about possible erroneous usage.

@item -d @var{d}
@itemx --delimiter=@var{d}
@opindex -d
@opindex --delimiter
Use the character @var{d} as input field separator (default: whitespace).
@emph{Note}: Using non-default delimiter turns off automatic padding.

@item --field=@var{fields}
@opindex --field
Convert the number in input field @var{fields} (default: 1).
@var{fields} supports @command{cut} style field ranges:

@example
N    N'th field, counted from 1
N-   from N'th field, to end of line
N-M  from N'th to M'th field (inclusive)
-M   from first to M'th field (inclusive)
-    all fields
@end example


@item --format=@var{format}
@opindex --format
Use printf-style floating FORMAT string.  The @var{format} string must contain
one @samp{%f} directive, optionally with @samp{'}, @samp{-}, @samp{0}, width
or precision modifiers.  The @samp{'} modifier will enable @option{--grouping},
the @samp{-} modifier will enable left-aligned @option{--padding} and the width
modifier will enable right-aligned @option{--padding}.  The @samp{0} width
modifier (without the @samp{-} modifier) will generate leading zeros on the
number, up to the specified width.  A precision specification like @samp{%.1f}
will override the precision determined from the input data or set due to
@option{--to} option auto scaling.

@item --from=@var{unit}
@opindex --from
Auto-scales input numbers according to @var{unit}.  See UNITS below.
The default is no scaling, meaning suffixes (e.g. @samp{M}, @samp{G}) will
trigger an error.

@item --from-unit=@var{n}
@opindex --from-unit
Specify the input unit size (instead of the default 1).  Use this option when
the input numbers represent other units (e.g. if the input number @samp{10}
represents 10 units of 512 bytes, use @samp{--from-unit=512}).
Suffixes are handled as with @samp{--from=auto}.

@item --grouping
@opindex --grouping
Group digits in output numbers according to the current locale's grouping rules
(e.g @emph{Thousands Separator} character, commonly @samp{.} (dot) or @samp{,}
comma).  This option has no effect in @samp{POSIX/C} locale.

@item --header[=@var{n}]
@opindex --header
@opindex --header=N
Print the first @var{n} (default: 1) lines without any conversion.

@item --invalid=@var{mode}
@opindex --invalid
The default action on input errors is to exit immediately with status code 2.
@option{--invalid=@samp{abort}} explicitly specifies this default mode.
With a @var{mode} of @samp{fail}, print a warning for @emph{each} conversion
error, and exit with status 2.  With a @var{mode} of @samp{warn}, exit with
status 0, even in the presence of conversion errors, and with a @var{mode} of
@samp{ignore} do not even print diagnostics.

@item --padding=@var{n}
@opindex --padding
Pad the output numbers to @var{n} characters, by adding spaces.  If @var{n} is
a positive number, numbers will be right-aligned.  If @var{n} is a negative
number, numbers will be left-aligned.  By default, numbers are automatically
aligned based on the input line's width (only with the default delimiter).

@item --round=@var{method}
@opindex --round
@opindex --round=up
@opindex --round=down
@opindex --round=from-zero
@opindex --round=towards-zero
@opindex --round=nearest
When converting number representations, round the number according to
@var{method}, which can be @samp{up}, @samp{down},
@samp{from-zero} (the default), @samp{towards-zero}, @samp{nearest}.

@item --suffix=@var{suffix}
@opindex --suffix
Add @samp{SUFFIX} to the output numbers, and accept optional @samp{SUFFIX} in
input numbers.

@item --to=@var{unit}
@opindex --to
Auto-scales output numbers according to @var{unit}.  See @emph{Units} below.
The default is no scaling, meaning all the digits of the number are printed.

@item --to-unit=@var{n}
@opindex --to-unit
Specify the output unit size (instead of the default 1).  Use this option when
the output numbers represent other units (e.g. to represent @samp{4,000,000}
bytes in blocks of 1KB, use @samp{--to=si --to-unit=1000}).
Suffixes are handled as with @samp{--from=auto}.

@optZeroTerminated
@newlineFieldSeparator

@end table

@subsection Possible @var{unit}s:

The following are the possible @var{unit} options with @option{--from=UNITS} and
@option{--to=UNITS}:

@table @var

@item none
No scaling is performed.  For input numbers, no suffixes are accepted, and any
trailing characters following the number will trigger an error.  For output
numbers, all digits of the numbers will be printed.

@item si
Auto-scale numbers according to the @emph{International System of Units (SI)}
standard.
For input numbers, accept one of the following suffixes.
For output numbers, values larger than 1000 will be rounded, and printed with
one of the following suffixes:

@example
@samp{K}  =>  @math{1000^1 = 10^3} (Kilo)
@samp{M}  =>  @math{1000^2 = 10^6} (Mega)
@samp{G}  =>  @math{1000^3 = 10^9} (Giga)
@samp{T}  =>  @math{1000^4 = 10^{12}} (Tera)
@samp{P}  =>  @math{1000^5 = 10^{15}} (Peta)
@samp{E}  =>  @math{1000^6 = 10^{18}} (Exa)
@samp{Z}  =>  @math{1000^7 = 10^{21}} (Zetta)
@samp{Y}  =>  @math{1000^8 = 10^{24}} (Yotta)
@end example

@item iec
Auto-scale numbers according to the @emph{International Electrotechnical
Commission (IEC)} standard.
For input numbers, accept one of the following suffixes.
For output numbers, values larger than 1024 will be rounded, and printed with
one of the following suffixes:

@example
@samp{K}  =>  @math{1024^1 = 2^{10}} (Kibi)
@samp{M}  =>  @math{1024^2 = 2^{20}} (Mebi)
@samp{G}  =>  @math{1024^3 = 2^{30}} (Gibi)
@samp{T}  =>  @math{1024^4 = 2^{40}} (Tebi)
@samp{P}  =>  @math{1024^5 = 2^{50}} (Pebi)
@samp{E}  =>  @math{1024^6 = 2^{60}} (Exbi)
@samp{Z}  =>  @math{1024^7 = 2^{70}} (Zebi)
@samp{Y}  =>  @math{1024^8 = 2^{80}} (Yobi)
@end example

The @option{iec} option uses a single letter suffix (e.g. @samp{G}), which is
not fully standard, as the @emph{iec} standard recommends a two-letter symbol
(e.g @samp{Gi}) - but in practice, this method common.  Compare with
the @option{iec-i} option.

@item iec-i
Auto-scale numbers according to the @emph{International Electrotechnical
Commission (IEC)} standard.
For input numbers, accept one of the following suffixes.
For output numbers, values larger than 1024 will be rounded, and printed with
one of the following suffixes:

@example
@samp{Ki}  =>  @math{1024^1 = 2^{10}} (Kibi)
@samp{Mi}  =>  @math{1024^2 = 2^{20}} (Mebi)
@samp{Gi}  =>  @math{1024^3 = 2^{30}} (Gibi)
@samp{Ti}  =>  @math{1024^4 = 2^{40}} (Tebi)
@samp{Pi}  =>  @math{1024^5 = 2^{50}} (Pebi)
@samp{Ei}  =>  @math{1024^6 = 2^{60}} (Exbi)
@samp{Zi}  =>  @math{1024^7 = 2^{70}} (Zebi)
@samp{Yi}  =>  @math{1024^8 = 2^{80}} (Yobi)
@end example

The @option{iec-i} option uses a two-letter suffix symbol (e.g. @samp{Gi}),
as the @emph{iec} standard recommends, but this is not always common in
practice.  Compare with the @option{iec} option.

@item auto
@samp{auto} can only be used with @option{--from}.  With this method, numbers
with @samp{K},@samp{M},@samp{G},@samp{T},@samp{P},@samp{E},@samp{Z},@samp{Y}
suffixes are interpreted as @emph{SI} values, and numbers with @samp{Ki},
@samp{Mi},@samp{Gi},@samp{Ti},@samp{Pi},@samp{Ei},@samp{Zi},@samp{Yi} suffixes
are interpreted as @emph{IEC} values.

@end table

@subsection Examples of using @command{numfmt}

Converting a single number from/to @emph{human} representation:
@example
$ numfmt --to=si 500000
500K

$ numfmt --to=iec 500000
489K

$ numfmt --to=iec-i 500000
489Ki

$ numfmt --from=si 1M
1000000

$ numfmt --from=iec 1M
1048576

# with '--from=auto', M=Mega, Mi=Mebi
$ numfmt --from=auto 1M
1000000
$ numfmt --from=auto 1Mi
1048576
@end example

Converting from @samp{SI} to @samp{IEC} scales (e.g. when a harddisk capacity is
advertised as @samp{1TB}, while checking the drive's capacity gives lower
values):

@example
$ numfmt --from=si --to=iec 1T
932G
@end example


Converting a single field from an input file / piped input (these contrived
examples are for demonstration purposes only, as both @command{ls} and
@command{df} support the @option{--human-readable} option to
output sizes in human-readable format):

@example
# Third field (file size) will be shown in SI representation
$ ls -log | numfmt --field 3 --header --to=si | head -n4
-rw-r--r--  1     94K Aug 23  2011 ABOUT-NLS
-rw-r--r--  1    3.7K Jan  7 16:15 AUTHORS
-rw-r--r--  1     36K Jun  1  2011 COPYING
-rw-r--r--  1       0 Jan  7 15:15 ChangeLog

# Second field (size) will be shown in IEC representation
$ df --block-size=1 | numfmt --field 2 --header --to=iec | head -n4
File system   1B-blocks        Used  Available Use% Mounted on
rootfs             132G   104741408   26554036  80% /
tmpfs              794M        7580     804960   1% /run/shm
/dev/sdb1          694G   651424756   46074696  94% /home
@end example


Output can be tweaked using @option{--padding} or @option{--format}:

@example
# Pad to 10 characters, right-aligned
$ du -s * | numfmt --to=si --padding=10
      2.5K config.log
       108 config.status
      1.7K configure
        20 configure.ac

# Pad to 10 characters, left-aligned
$ du -s * | numfmt --to=si --padding=-10
2.5K       config.log
108        config.status
1.7K       configure
20         configure.ac

# Pad to 10 characters, left-aligned, using 'format'
$ du -s * | numfmt --to=si --format="%10f"
      2.5K config.log
       108 config.status
      1.7K configure
        20 configure.ac

# Pad to 10 characters, left-aligned, using 'format'
$ du -s * | numfmt --to=si --padding="%-10f"
2.5K       config.log
108        config.status
1.7K       configure
20         configure.ac
@end example

With locales that support grouping digits, using @option{--grouping} or
@option{--format} enables grouping.  In @samp{POSIX} locale, grouping is
silently ignored:

@example
$ LC_ALL=C numfmt --from=iec --grouping 2G
2147483648

$ LC_ALL=en_US.utf8 numfmt --from=iec --grouping 2G
2,147,483,648

$ LC_ALL=ta_IN numfmt --from=iec --grouping 2G
2,14,74,83,648

$ LC_ALL=C ./src/numfmt --from=iec --format="==%'15f==" 2G
==     2147483648==

$ LC_ALL=en_US.utf8 ./src/numfmt --from=iec --format="==%'15f==" 2G
==  2,147,483,648==

$ LC_ALL=en_US.utf8 ./src/numfmt --from=iec --format="==%'-15f==" 2G
==2,147,483,648  ==

$ LC_ALL=ta_IN ./src/numfmt --from=iec --format="==%'15f==" 2G
== 2,14,74,83,648==
@end example


@node seq invocation
@section @command{seq}: Print numeric sequences

@pindex seq
@cindex numeric sequences
@cindex sequence of numbers

@command{seq} prints a sequence of numbers to standard output.  Synopses:

@example
seq [@var{option}]@dots{} @var{last}
seq [@var{option}]@dots{} @var{first} @var{last}
seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
@end example

@command{seq} prints the numbers from @var{first} to @var{last} by
@var{increment}.  By default, each number is printed on a separate line.
When @var{increment} is not specified, it defaults to @samp{1},
even when @var{first} is larger than @var{last}.
@var{first} also defaults to @samp{1}.  So @code{seq 1} prints
@samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
The sequence of numbers ends when the sum of the current number and
@var{increment} would become greater than @var{last},
so @code{seq 1 10 10} only produces @samp{1}.
@var{increment} must not be @samp{0}; use @command{yes} to get
repeated output of a constant number.
@var{first}, @var{increment} and @var{last} must not be @code{NaN}.
Floating-point numbers may be specified.  @xref{Floating point}.

The program accepts the following options.  Also see @ref{Common options}.
Options must precede operands.

@table @samp
@item -f @var{format}
@itemx --format=@var{format}
@opindex -f
@opindex --format
@cindex formatting of numbers in @command{seq}
Print all numbers using @var{format}.
@var{format} must contain exactly one of the @samp{printf}-style
floating point conversion specifications @samp{%a}, @samp{%e},
@samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}@.
The @samp{%} may be followed by zero or more flags taken from the set
@samp{-+#0 '}, then an optional width containing one or more digits,
then an optional precision consisting of a @samp{.} followed by zero
or more digits.  @var{format} may also contain any number of @samp{%%}
conversion specifications.  All conversion specifications have the
same meaning as with @samp{printf}.

The default format is derived from @var{first}, @var{step}, and
@var{last}.  If these all use a fixed point decimal representation,
the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
precision that can represent the output numbers exactly.  Otherwise,
the default format is @samp{%g}.

@item -s @var{string}
@itemx --separator=@var{string}
@opindex -s
@opindex --separator
@cindex separator for numbers in @command{seq}
Separate numbers with @var{string}; default is a newline.
The output always terminates with a newline.

@item -w
@itemx --equal-width
@opindex -w
@opindex --equal-width
Print all numbers with the same width, by padding with leading zeros.
@var{first}, @var{step}, and @var{last} should all use a fixed point
decimal representation.
(To have other kinds of padding, use @option{--format}).

@end table

You can get finer-grained control over output with @option{-f}:

@example
$ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
(-9.00E+05)
( 2.00E+05)
( 1.30E+06)
@end example

If you want hexadecimal integer output, you can use @command{printf}
to perform the conversion:

@example
$ printf '%x\n' $(seq 1048575 1024 1050623)
fffff
1003ff
1007ff
@end example

For very long lists of numbers, use xargs to avoid
system limitations on the length of an argument list:

@example
$ seq 1000000 | xargs printf '%x\n' | tail -n 3
f423e
f423f
f4240
@end example

To generate octal output, use the printf @code{%o} format instead
of @code{%x}.

On most systems, seq can produce whole-number output for values up to
at least @math{2^{53}}.  Larger integers are approximated.  The details
differ depending on your floating-point implementation.
@xref{Floating point}.  A common
case is that @command{seq} works with integers through @math{2^{64}},
and larger integers may not be numerically correct:

@example
$ seq 50000000000000000000 2 50000000000000000004
50000000000000000000
50000000000000000000
50000000000000000004
@end example

However, note that when limited to non-negative whole numbers,
an increment of 1 and no format-specifying option, seq can print
arbitrarily large numbers.

Be careful when using @command{seq} with outlandish values: otherwise
you may see surprising results, as @command{seq} uses floating point
internally.  For example, on the x86 platform, where the internal
representation uses a 64-bit fraction, the command:

@example
seq 1 0.0000000000000000001 1.0000000000000000009
@end example

outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.

@exitstatus


@node File permissions
@chapter File permissions
@include perm.texi

@include parse-datetime.texi

@c              What's GNU?
@c              Arnold Robbins
@node Opening the software toolbox
@chapter Opening the Software Toolbox

An earlier version of this chapter appeared in
@uref{http://www.linuxjournal.com/article.php?sid=2762, the
@cite{What's GNU@?} column of the June 1994 @cite{Linux Journal}}.
It was written by Arnold Robbins.

@menu
* Toolbox introduction::        Toolbox introduction
* I/O redirection::             I/O redirection
* The who command::             The @command{who} command
* The cut command::             The @command{cut} command
* The sort command::            The @command{sort} command
* The uniq command::            The @command{uniq} command
* Putting the tools together::  Putting the tools together
@end menu


@node Toolbox introduction
@unnumberedsec Toolbox Introduction

This month's column is only peripherally related to the GNU Project, in
that it describes a number of the GNU tools on your GNU/Linux system
and how they
might be used.  What it's really about is the ``Software Tools'' philosophy
of program development and usage.

The software tools philosophy was an important and integral concept
in the initial design and development of Unix (of which Linux and GNU are
essentially clones).  Unfortunately, in the modern day press of
Internetworking and flashy GUIs, it seems to have fallen by the
wayside.  This is a shame, since it provides a powerful mental model
for solving many kinds of problems.

Many people carry a Swiss Army knife around in their pants pockets (or
purse).  A Swiss Army knife is a handy tool to have: it has several knife
blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
a number of other things on it.  For the everyday, small miscellaneous jobs
where you need a simple, general purpose tool, it's just the thing.

On the other hand, an experienced carpenter doesn't build a house using
a Swiss Army knife.  Instead, he has a toolbox chock full of specialized
tools---a saw, a hammer, a screwdriver, a plane, and so on.  And he knows
exactly when and where to use each tool; you won't catch him hammering nails
with the handle of his screwdriver.

The Unix developers at Bell Labs were all professional programmers and trained
computer scientists.  They had found that while a one-size-fits-all program
might appeal to a user because there's only one program to use, in practice
such programs are

@enumerate a
@item
difficult to write,

@item
difficult to maintain and
debug, and

@item
difficult to extend to meet new situations.
@end enumerate

Instead, they felt that programs should be specialized tools.  In short, each
program ``should do one thing well.''  No more and no less.  Such programs are
simpler to design, write, and get right---they only do one thing.

Furthermore, they found that with the right machinery for hooking programs
together, that the whole was greater than the sum of the parts.  By combining
several special purpose programs, you could accomplish a specific task
that none of the programs was designed for, and accomplish it much more
quickly and easily than if you had to write a special purpose program.
We will see some (classic) examples of this further on in the column.
(An important additional point was that, if necessary, take a detour
and build any software tools you may need first, if you don't already
have something appropriate in the toolbox.)

@node I/O redirection
@unnumberedsec I/O Redirection

Hopefully, you are familiar with the basics of I/O redirection in the
shell, in particular the concepts of ``standard input,'' ``standard output,''
and ``standard error''.  Briefly, ``standard input'' is a data source, where
data comes from.  A program should not need to either know or care if the
data source is a disk file, a keyboard, a magnetic tape, or even a punched
card reader.  Similarly, ``standard output'' is a data sink, where data goes
to.  The program should neither know nor care where this might be.
Programs that only read their standard input, do something to the data,
and then send it on, are called @dfn{filters}, by analogy to filters in a
water pipeline.

With the Unix shell, it's very easy to set up data pipelines:

@smallexample
program_to_create_data | filter1 | ... | filterN > final.pretty.data
@end smallexample

We start out by creating the raw data; each filter applies some successive
transformation to the data, until by the time it comes out of the pipeline,
it is in the desired form.

This is fine and good for standard input and standard output.  Where does the
standard error come in to play?  Well, think about @command{filter1} in
the pipeline above.  What happens if it encounters an error in the data it
sees?  If it writes an error message to standard output, it will just
disappear down the pipeline into @command{filter2}'s input, and the
user will probably never see it.  So programs need a place where they can send
error messages so that the user will notice them.  This is standard error,
and it is usually connected to your console or window, even if you have
redirected standard output of your program away from your screen.

For filter programs to work together, the format of the data has to be
agreed upon.  The most straightforward and easiest format to use is simply
lines of text.  Unix data files are generally just streams of bytes, with
lines delimited by the ASCII LF (Line Feed) character,
conventionally called a ``newline'' in the Unix literature.  (This is
@code{'\n'} if you're a C programmer.)  This is the format used by all
the traditional filtering programs.  (Many earlier operating systems
had elaborate facilities and special purpose programs for managing
binary data.  Unix has always shied away from such things, under the
philosophy that it's easiest to simply be able to view and edit your
data with a text editor.)

OK, enough introduction.  Let's take a look at some of the tools, and then
we'll see how to hook them together in interesting ways.   In the following
discussion, we will only present those command line options that interest
us.  As you should always do, double check your system documentation
for the full story.

@node The who command
@unnumberedsec The @command{who} Command

The first program is the @command{who} command.  By itself, it generates a
list of the users who are currently logged in.  Although I'm writing
this on a single-user system, we'll pretend that several people are
logged in:

@example
$ who
@print{} arnold   console Jan 22 19:57
@print{} miriam   ttyp0   Jan 23 14:19(:0.0)
@print{} bill     ttyp1   Jan 21 09:32(:0.0)
@print{} arnold   ttyp2   Jan 23 20:48(:0.0)
@end example

Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
There are three people logged in, and I am logged in twice.  On traditional
Unix systems, user names are never more than eight characters long.  This
little bit of trivia will be useful later.  The output of @command{who} is nice,
but the data is not all that exciting.

@node The cut command
@unnumberedsec The @command{cut} Command

The next program we'll look at is the @command{cut} command.  This program
cuts out columns or fields of input data.  For example, we can tell it
to print just the login name and full name from the @file{/etc/passwd}
file.  The @file{/etc/passwd} file has seven fields, separated by
colons:

@example
arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
@end example

To get the first and fifth fields, we would use @command{cut} like this:

@example
$ cut -d: -f1,5 /etc/passwd
@print{} root:Operator
@dots{}
@print{} arnold:Arnold D. Robbins
@print{} miriam:Miriam A. Robbins
@dots{}
@end example

With the @option{-c} option, @command{cut} will cut out specific characters
(i.e., columns) in the input lines.  This is useful for input data
that has fixed width fields, and does not have a field separator.  For
example, list the Monday dates for the current month:

@c Is using cal ok?  Looked at gcal, but I don't like it.
@example
$ cal | cut -c 3-5
@print{}Mo
@print{}
@print{}  6
@print{} 13
@print{} 20
@print{} 27
@end example

@node The sort command
@unnumberedsec The @command{sort} Command

Next we'll look at the @command{sort} command.  This is one of the most
powerful commands on a Unix-style system; one that you will often find
yourself using when setting up fancy data plumbing.

The @command{sort}
command reads and sorts each file named on the command line.  It then
merges the sorted data and writes it to standard output.  It will read
standard input if no files are given on the command line (thus
making it into a filter).  The sort is based on the character collating
sequence or based on user-supplied ordering criteria.


@node The uniq command
@unnumberedsec The @command{uniq} Command

Finally (at least for now), we'll look at the @command{uniq} program.  When
sorting data, you will often end up with duplicate lines, lines that
are identical.  Usually, all you need is one instance of each line.
This is where @command{uniq} comes in.  The @command{uniq} program reads its
standard input.  It prints only one
copy of each repeated line.  It does have several options.  Later on,
we'll use the @option{-c} option, which prints each unique line, preceded
by a count of the number of times that line occurred in the input.


@node Putting the tools together
@unnumberedsec Putting the Tools Together

Now, let's suppose this is a large ISP server system with dozens of users
logged in.  The management wants the system administrator to write a
program that will
generate a sorted list of logged in users.  Furthermore, even if a user
is logged in multiple times, his or her name should only show up in the
output once.

The administrator could sit down with the system documentation and write a C
program that did this.  It would take perhaps a couple of hundred lines
of code and about two hours to write it, test it, and debug it.
However, knowing the software toolbox, the administrator can instead start out
by generating just a list of logged on users:

@example
$ who | cut -c1-8
@print{} arnold
@print{} miriam
@print{} bill
@print{} arnold
@end example

Next, sort the list:

@example
$ who | cut -c1-8 | sort
@print{} arnold
@print{} arnold
@print{} bill
@print{} miriam
@end example

Finally, run the sorted list through @command{uniq}, to weed out duplicates:

@example
$ who | cut -c1-8 | sort | uniq
@print{} arnold
@print{} bill
@print{} miriam
@end example

The @command{sort} command actually has a @option{-u} option that does what
@command{uniq} does.  However, @command{uniq} has other uses for which one
cannot substitute @samp{sort -u}.

The administrator puts this pipeline into a shell script, and makes it
available for
all the users on the system (@samp{#} is the system administrator,
or @code{root}, prompt):

@example
# cat > /usr/local/bin/listusers
who | cut -c1-8 | sort | uniq
^D
# chmod +x /usr/local/bin/listusers
@end example

There are four major points to note here.  First, with just four
programs, on one command line, the administrator was able to save about two
hours worth of work.  Furthermore, the shell pipeline is just about as
efficient as the C program would be, and it is much more efficient in
terms of programmer time.  People time is much more expensive than
computer time, and in our modern ``there's never enough time to do
everything'' society, saving two hours of programmer time is no mean
feat.

Second, it is also important to emphasize that with the
@emph{combination} of the tools, it is possible to do a special
purpose job never imagined by the authors of the individual programs.

Third, it is also valuable to build up your pipeline in stages, as we did here.
This allows you to view the data at each stage in the pipeline, which helps
you acquire the confidence that you are indeed using these tools correctly.

Finally, by bundling the pipeline in a shell script, other users can use
your command, without having to remember the fancy plumbing you set up for
them.  In terms of how you run them, shell scripts and compiled programs are
indistinguishable.

After the previous warm-up exercise, we'll look at two additional, more
complicated pipelines.  For them, we need to introduce two more tools.

The first is the @command{tr} command, which stands for ``transliterate.''
The @command{tr} command works on a character-by-character basis, changing
characters.  Normally it is used for things like mapping upper case to
lower case:

@example
$ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
@print{} this example has mixed case!
@end example

There are several options of interest:

@table @code
@item -c
work on the complement of the listed characters, i.e.,
operations apply to characters not in the given set

@item -d
delete characters in the first set from the output

@item -s
squeeze repeated characters in the output into just one character.
@end table

We will be using all three options in a moment.

The other command we'll look at is @command{comm}.  The @command{comm}
command takes two sorted input files as input data, and prints out the
files' lines in three columns.  The output columns are the data lines
unique to the first file, the data lines unique to the second file, and
the data lines that are common to both.  The @option{-1}, @option{-2}, and
@option{-3} command line options @emph{omit} the respective columns.  (This is
non-intuitive and takes a little getting used to.)  For example:

@example
$ cat f1
@print{} 11111
@print{} 22222
@print{} 33333
@print{} 44444
$ cat f2
@print{} 00000
@print{} 22222
@print{} 33333
@print{} 55555
$ comm f1 f2
@print{}         00000
@print{} 11111
@print{}                 22222
@print{}                 33333
@print{} 44444
@print{}         55555
@end example

The file name @file{-} tells @command{comm} to read standard input
instead of a regular file.

Now we're ready to build a fancy pipeline.  The first application is a word
frequency counter.  This helps an author determine if he or she is over-using
certain words.

The first step is to change the case of all the letters in our input file
to one case.  ``The'' and ``the'' are the same word when doing counting.

@example
$ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
@end example

The next step is to get rid of punctuation.  Quoted words and unquoted words
should be treated identically; it's easiest to just get the punctuation out of
the way.

@smallexample
$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
@end smallexample

The second @command{tr} command operates on the complement of the listed
characters, which are all the letters, the digits, the underscore, and
the blank.  The @samp{\n} represents the newline character; it has to
be left alone.  (The ASCII tab character should also be included for
good measure in a production script.)

At this point, we have data consisting of words separated by blank space.
The words only contain alphanumeric characters (and the underscore).  The
next step is break the data apart so that we have one word per line.  This
makes the counting operation much easier, as we will see shortly.

@smallexample
$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
> tr -s ' ' '\n' | ...
@end smallexample

This command turns blanks into newlines.  The @option{-s} option squeezes
multiple newline characters in the output into just one, removing
blank lines.  (The @samp{>} is the shell's ``secondary prompt.''
This is what the shell prints when it notices you haven't finished
typing in all of a command.)

We now have data consisting of one word per line, no punctuation, all one
case.  We're ready to count each word:

@smallexample
$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
> tr -s ' ' '\n' | sort | uniq -c | ...
@end smallexample

At this point, the data might look something like this:

@example
     60 a
      2 able
      6 about
      1 above
      2 accomplish
      1 acquire
      1 actually
      2 additional
@end example

The output is sorted by word, not by count!  What we want is the most
frequently used words first.  Fortunately, this is easy to accomplish,
with the help of two more @command{sort} options:

@table @code
@item -n
do a numeric sort, not a textual one

@item -r
reverse the order of the sort
@end table

The final pipeline looks like this:

@smallexample
$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
> tr -s ' ' '\n' | sort | uniq -c | sort -n -r
@print{}    156 the
@print{}     60 a
@print{}     58 to
@print{}     51 of
@print{}     51 and
@dots{}
@end smallexample

Whew!  That's a lot to digest.  Yet, the same principles apply.  With six
commands, on two lines (really one long one split for convenience), we've
created a program that does something interesting and useful, in much
less time than we could have written a C program to do the same thing.

A minor modification to the above pipeline can give us a simple spelling
checker!  To determine if you've spelled a word correctly, all you have to
do is look it up in a dictionary.  If it is not there, then chances are
that your spelling is incorrect.  So, we need a dictionary.
The conventional location for a dictionary is @file{/usr/dict/words}.
On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
revision of this article.}
this is a sorted, 45,402 word dictionary.

Now, how to compare our file with the dictionary?  As before, we generate
a sorted list of words, one per line:

@smallexample
$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
> tr -s ' ' '\n' | sort -u | ...
@end smallexample

Now, all we need is a list of words that are @emph{not} in the
dictionary.  Here is where the @command{comm} command comes in.

@smallexample
$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
> tr -s ' ' '\n' | sort -u |
> comm -23 - /usr/dict/words
@end smallexample

The @option{-2} and @option{-3} options eliminate lines that are only in the
dictionary (the second file), and lines that are in both files.  Lines
only in the first file (standard input, our stream of words), are
words that are not in the dictionary.  These are likely candidates for
spelling errors.  This pipeline was the first cut at a production
spelling checker on Unix.

There are some other tools that deserve brief mention.

@table @command
@item grep
search files for text that matches a regular expression

@item wc
count lines, words, characters

@item tee
a T-fitting for data pipes, copies data to files and to standard output

@item sed
the stream editor, an advanced tool

@item awk
a data manipulation language, another advanced tool
@end table

The software tools philosophy also espoused the following bit of
advice: ``Let someone else do the hard part.''  This means, take
something that gives you most of what you need, and then massage it the
rest of the way until it's in the form that you want.

To summarize:

@enumerate 1
@item
Each program should do one thing well.  No more, no less.

@item
Combining programs with appropriate plumbing leads to results where
the whole is greater than the sum of the parts.  It also leads to novel
uses of programs that the authors might never have imagined.

@item
Programs should never print extraneous header or trailer data, since these
could get sent on down a pipeline.  (A point we didn't mention earlier.)

@item
Let someone else do the hard part.

@item
Know your toolbox!  Use each program appropriately.  If you don't have an
appropriate tool, build one.
@end enumerate

As of this writing, all the programs discussed are available from
@uref{http://ftp.gnu.org/old-gnu/textutils/textutils-1.22.tar.gz},
with more recent versions available from
@uref{http://ftp.gnu.org/gnu/coreutils}.

None of what I have presented in this column is new.  The Software Tools
philosophy was first introduced in the book @cite{Software Tools}, by
Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
This book showed how to write and use software tools.  It was written in
1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
FORtran).  At the time, C was not as ubiquitous as it is now; FORTRAN
was.  The last chapter presented a @command{ratfor} to FORTRAN
processor, written in @command{ratfor}.  @command{ratfor} looks an awful
lot like C; if you know C, you won't have any problem following the
code.

In 1981, the book was updated and made available as @cite{Software Tools
in Pascal} (Addison-Wesley, ISBN 0-201-10342-7).  Both books are
still in print and are well worth
reading if you're a programmer.  They certainly made a major change in
how I view programming.

The programs in both books are available from
@uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
For a number of years, there was an active
Software Tools Users Group, whose members had ported the original
@command{ratfor} programs to essentially every computer system with a
FORTRAN compiler.  The popularity of the group waned in the middle 1980s
as Unix began to spread beyond universities.

With the current proliferation of GNU code and other clones of Unix programs,
these programs now receive little attention; modern C versions are
much more efficient and do more than these programs do.  Nevertheless, as
exposition of good programming style, and evangelism for a still-valuable
philosophy, these books are unparalleled, and I recommend them highly.

Acknowledgment: I would like to express my gratitude to Brian Kernighan
of Bell Labs, the original Software Toolsmith, for reviewing this column.

@node GNU Free Documentation License
@appendix GNU Free Documentation License

@include fdl.texi

@node Concept index
@unnumbered Index

@printindex cp

@bye

@c Local variables:
@c texinfo-column-for-description: 32
@c End: