summaryrefslogtreecommitdiff
path: root/src/tac.c
blob: 7b06de71585ae6ba571087f5cfeee5640de083b8 (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
/* tac - concatenate and print files in reverse
   Copyright (C) 1988-1991, 1995-2001 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/* Written by Jay Lepreau (lepreau@cs.utah.edu).
   GNU enhancements by David MacKenzie (djm@gnu.ai.mit.edu). */

/* Copy each FILE, or the standard input if none are given or when a
   FILE name of "-" is encountered, to the standard output with the
   order of the records reversed.  The records are separated by
   instances of a string, or a newline if none is given.  By default, the
   separator string is attached to the end of the record that it
   follows in the file.

   Options:
   -b, --before			The separator is attached to the beginning
				of the record that it precedes in the file.
   -r, --regex			The separator is a regular expression.
   -s, --separator=separator	Use SEPARATOR as the record separator.

   To reverse a file byte by byte, use (in bash, ksh, or sh):
tac -r -s '.\|
' file */

#include <config.h>

#include <stdio.h>
#include <getopt.h>
#include <sys/types.h>
#include "system.h"
#include "closeout.h"

#include <regex.h>

#include "error.h"
#include "safe-read.h"

/* The official name of this program (e.g., no `g' prefix).  */
#define PROGRAM_NAME "tac"

#define AUTHORS N_ ("Jay Lepreau and David MacKenzie")

#if defined __MSDOS__ || defined _WIN32
/* Define this to non-zero on systems for which the regular mechanism
   (of unlinking an open file and expecting to be able to write, seek
   back to the beginning, then reread it) doesn't work.  E.g., on Windows
   and DOS systems.  */
# define DONT_UNLINK_WHILE_OPEN 1
#endif


#ifndef DEFAULT_TMPDIR
# define DEFAULT_TMPDIR "/tmp"
#endif

/* The number of bytes per atomic read. */
#define INITIAL_READSIZE 8192

/* The number of bytes per atomic write. */
#define WRITESIZE 8192

/* The name this program was run with. */
char *program_name;

/* The string that separates the records of the file. */
static char *separator;

/* If nonzero, print `separator' along with the record preceding it
   in the file; otherwise with the record following it. */
static int separator_ends_record;

/* 0 if `separator' is to be matched as a regular expression;
   otherwise, the length of `separator', used as a sentinel to
   stop the search. */
static int sentinel_length;

/* The length of a match with `separator'.  If `sentinel_length' is 0,
   `match_length' is computed every time a match succeeds;
   otherwise, it is simply the length of `separator'. */
static int match_length;

/* The input buffer. */
static char *G_buffer;

/* The number of bytes to read at once into `buffer'. */
static size_t read_size;

/* The size of `buffer'.  This is read_size * 2 + sentinel_length + 2.
   The extra 2 bytes allow `past_end' to have a value beyond the
   end of `G_buffer' and `match_start' to run off the front of `G_buffer'. */
static unsigned G_buffer_size;

/* The compiled regular expression representing `separator'. */
static struct re_pattern_buffer compiled_separator;

static struct option const longopts[] =
{
  {"before", no_argument, NULL, 'b'},
  {"regex", no_argument, NULL, 'r'},
  {"separator", required_argument, NULL, 's'},
  {GETOPT_HELP_OPTION_DECL},
  {GETOPT_VERSION_OPTION_DECL},
  {NULL, 0, NULL, 0}
};

void
usage (int status)
{
  if (status != 0)
    fprintf (stderr, _("Try `%s --help' for more information.\n"),
	     program_name);
  else
    {
      printf (_("\
Usage: %s [OPTION]... [FILE]...\n\
"),
	      program_name);
      printf (_("\
Write each FILE to standard output, last line first.\n\
With no FILE, or when FILE is -, read standard input.\n\
\n\
  -b, --before             attach the separator before instead of after\n\
  -r, --regex              interpret the separator as a regular expression\n\
  -s, --separator=STRING   use STRING as the separator instead of newline\n\
      --help               display this help and exit\n\
      --version            output version information and exit\n\
"));
      puts (_("\nReport bugs to <bug-textutils@gnu.org>."));
    }
  exit (status == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
}

/* Print the characters from START to PAST_END - 1.
   If START is NULL, just flush the buffer. */

static void
output (const char *start, const char *past_end)
{
  static char buffer[WRITESIZE];
  static int bytes_in_buffer = 0;
  int bytes_to_add = past_end - start;
  int bytes_available = WRITESIZE - bytes_in_buffer;

  if (start == 0)
    {
      fwrite (buffer, 1, bytes_in_buffer, stdout);
      bytes_in_buffer = 0;
      return;
    }

  /* Write out as many full buffers as possible. */
  while (bytes_to_add >= bytes_available)
    {
      memcpy (buffer + bytes_in_buffer, start, bytes_available);
      bytes_to_add -= bytes_available;
      start += bytes_available;
      fwrite (buffer, 1, WRITESIZE, stdout);
      bytes_in_buffer = 0;
      bytes_available = WRITESIZE;
    }

  memcpy (buffer + bytes_in_buffer, start, bytes_to_add);
  bytes_in_buffer += bytes_to_add;
}

/* Print in reverse the file open on descriptor FD for reading FILE.
   Return 0 if ok, 1 if an error occurs. */

static int
tac_seekable (int input_fd, const char *file)
{
  /* Pointer to the location in `G_buffer' where the search for
     the next separator will begin. */
  char *match_start;

  /* Pointer to one past the rightmost character in `G_buffer' that
     has not been printed yet. */
  char *past_end;

  /* Length of the record growing in `G_buffer'. */
  size_t saved_record_size;

  /* Offset in the file of the next read. */
  off_t file_pos;

  /* Nonzero if `output' has not been called yet for any file.
     Only used when the separator is attached to the preceding record. */
  int first_time = 1;
  char first_char = *separator;	/* Speed optimization, non-regexp. */
  char *separator1 = separator + 1; /* Speed optimization, non-regexp. */
  int match_length1 = match_length - 1; /* Speed optimization, non-regexp. */
  struct re_registers regs;

  /* Find the size of the input file. */
  file_pos = lseek (input_fd, (off_t) 0, SEEK_END);
  if (file_pos < 1)
    return 0;			/* It's an empty file. */

  /* Arrange for the first read to lop off enough to leave the rest of the
     file a multiple of `read_size'.  Since `read_size' can change, this may
     not always hold during the program run, but since it usually will, leave
     it here for i/o efficiency (page/sector boundaries and all that).
     Note: the efficiency gain has not been verified. */
  saved_record_size = file_pos % read_size;
  if (saved_record_size == 0)
    saved_record_size = read_size;
  file_pos -= saved_record_size;
  /* `file_pos' now points to the start of the last (probably partial) block
     in the input file. */

  if (lseek (input_fd, file_pos, SEEK_SET) < 0)
    error (0, errno, "%s: seek failed", file);

  if (safe_read (input_fd, G_buffer, saved_record_size) != saved_record_size)
    {
      error (0, errno, "%s", file);
      return 1;
    }

  match_start = past_end = G_buffer + saved_record_size;
  /* For non-regexp search, move past impossible positions for a match. */
  if (sentinel_length)
    match_start -= match_length1;

  for (;;)
    {
      /* Search backward from `match_start' - 1 to `G_buffer' for a match
	 with `separator'; for speed, use strncmp if `separator' contains no
	 metacharacters.
	 If the match succeeds, set `match_start' to point to the start of
	 the match and `match_length' to the length of the match.
	 Otherwise, make `match_start' < `G_buffer'. */
      if (sentinel_length == 0)
	{
	  int i = match_start - G_buffer;
	  int ret;

	  ret = re_search (&compiled_separator, G_buffer, i, i - 1, -i, &regs);
	  if (ret == -1)
	    match_start = G_buffer - 1;
	  else if (ret == -2)
	    {
	      error (EXIT_FAILURE, 0,
		     _("error in regular expression search"));
	    }
	  else
	    {
	      match_start = G_buffer + regs.start[0];
	      match_length = regs.end[0] - regs.start[0];
	    }
	}
      else
	{
	  /* `match_length' is constant for non-regexp boundaries. */
	  while (*--match_start != first_char
		 || (match_length1 && strncmp (match_start + 1, separator1,
					       match_length1)))
	    /* Do nothing. */ ;
	}

      /* Check whether we backed off the front of `G_buffer' without finding
         a match for `separator'. */
      if (match_start < G_buffer)
	{
	  if (file_pos == 0)
	    {
	      /* Hit the beginning of the file; print the remaining record. */
	      output (G_buffer, past_end);
	      return 0;
	    }

	  saved_record_size = past_end - G_buffer;
	  if (saved_record_size > read_size)
	    {
	      /* `G_buffer_size' is about twice `read_size', so since
		 we want to read in another `read_size' bytes before
		 the data already in `G_buffer', we need to increase
		 `G_buffer_size'. */
	      char *newbuffer;
	      int offset = sentinel_length ? sentinel_length : 1;

	      read_size *= 2;
	      G_buffer_size = read_size * 2 + sentinel_length + 2;
	      newbuffer = xrealloc (G_buffer - offset, G_buffer_size);
	      newbuffer += offset;
	      /* Adjust the pointers for the new buffer location.  */
	      match_start += newbuffer - G_buffer;
	      past_end += newbuffer - G_buffer;
	      G_buffer = newbuffer;
	    }

	  /* Back up to the start of the next bufferfull of the file.  */
	  if (file_pos >= read_size)
	    file_pos -= read_size;
	  else
	    {
	      read_size = file_pos;
	      file_pos = 0;
	    }
	  lseek (input_fd, file_pos, SEEK_SET);

	  /* Shift the pending record data right to make room for the new.
	     The source and destination regions probably overlap.  */
	  memmove (G_buffer + read_size, G_buffer, saved_record_size);
	  past_end = G_buffer + read_size + saved_record_size;
	  /* For non-regexp searches, avoid unneccessary scanning. */
	  if (sentinel_length)
	    match_start = G_buffer + read_size;
	  else
	    match_start = past_end;

	  if (safe_read (input_fd, G_buffer, read_size) != read_size)
	    {
	      error (0, errno, "%s", file);
	      return 1;
	    }
	}
      else
	{
	  /* Found a match of `separator'. */
	  if (separator_ends_record)
	    {
	      char *match_end = match_start + match_length;

	      /* If this match of `separator' isn't at the end of the
	         file, print the record. */
	      if (first_time == 0 || match_end != past_end)
		output (match_end, past_end);
	      past_end = match_end;
	      first_time = 0;
	    }
	  else
	    {
	      output (match_start, past_end);
	      past_end = match_start;
	    }

	  /* For non-regex matching, we can back up.  */
	  if (sentinel_length > 0)
	    match_start -= match_length - 1;
	}
    }
}

/* Print FILE in reverse.
   Return 0 if ok, 1 if an error occurs. */

static int
tac_file (const char *file)
{
  int errors;
  FILE *in;

  in = fopen (file, "r");
  if (in == NULL)
    {
      error (0, errno, "%s", file);
      return 1;
    }
  SET_BINARY (fileno (in));
  errors = tac_seekable (fileno (in), file);
  if (ferror (in) || fclose (in) == EOF)
    {
      error (0, errno, "%s", file);
      return 1;
    }
  return errors;
}

#if DONT_UNLINK_WHILE_OPEN

static const char *file_to_remove;
static FILE *fp_to_close;

static void
unlink_tempfile (void)
{
  fclose (fp_to_close);
  unlink (file_to_remove);
}

static void
record_tempfile (const char *fn, FILE *fp)
{
  if (!file_to_remove)
    {
      file_to_remove = fn;
      fp_to_close = fp;
      atexit (unlink_tempfile);
    }
}

#endif

/* Make a copy of the standard input in `FIXME'. */

static void
save_stdin (FILE **g_tmp, char **g_tempfile)
{
  static char *template = NULL;
  static char *tempdir;
  char *tempfile;
  FILE *tmp;
  ssize_t bytes_read;
  int fd;

  if (template == NULL)
    {
      tempdir = getenv ("TMPDIR");
      if (tempdir == NULL)
	tempdir = DEFAULT_TMPDIR;
      template = xmalloc (strlen (tempdir) + 11);
    }
  sprintf (template, "%s/tacXXXXXX", tempdir);
  tempfile = template;
  fd = mkstemp (template);
  if (fd == -1)
    error (EXIT_FAILURE, errno, "%s", tempfile);

  tmp = fdopen (fd, "w+");
  if (tmp == NULL)
    error (EXIT_FAILURE, errno, "%s", tempfile);

#if DONT_UNLINK_WHILE_OPEN
  record_tempfile (tempfile, tmp);
#else
  unlink (tempfile);
#endif

  while (1)
    {
      bytes_read = safe_read (STDIN_FILENO, G_buffer, read_size);
      if (bytes_read == 0)
	break;
      if (bytes_read < 0)
	error (EXIT_FAILURE, errno, _("stdin: read error"));

      /* Don't bother checking for failure inside the loop -- check after.  */
      fwrite (G_buffer, 1, bytes_read, tmp);
    }

  if (ferror (tmp) || fflush (tmp) == EOF)
    error (EXIT_FAILURE, errno, "%s", tempfile);

  rewind (tmp);

  SET_BINARY (fileno (tmp));
  *g_tmp = tmp;
  *g_tempfile = tempfile;
}

/* Print the standard input in reverse, saving it to temporary
   file first if it is a pipe.
   Return 0 if ok, 1 if an error occurs. */

static int
tac_stdin (void)
{
  int errors;
  struct stat stats;

  /* No tempfile is needed for "tac < file".
     Use fstat instead of checking for errno == ESPIPE because
     lseek doesn't work on some special files but doesn't return an
     error, either. */
  if (fstat (STDIN_FILENO, &stats))
    {
      error (0, errno, _("standard input"));
      return 1;
    }

  if (S_ISREG (stats.st_mode))
    {
      errors = tac_seekable (fileno (stdin), _("standard input"));
    }
  else
    {
      FILE *tmp_stream;
      char *tmp_file;
      save_stdin (&tmp_stream, &tmp_file);
      errors = tac_seekable (fileno (tmp_stream), tmp_file);
    }

  return errors;
}

#if 0
/* BUF_END points one byte past the end of the buffer to be searched.  */

static void *
memrchr (const char *buf_start, const char *buf_end, int c)
{
  const char *p = buf_end;
  while (buf_start <= --p)
    {
      if (*(const unsigned char *) p == c)
	return (void *) p;
    }
  return NULL;
}

/* FIXME: describe */

static int
tac_mem (const char *buf, size_t n_bytes, FILE *out)
{
  const char *nl;
  const char *bol;

  if (n_bytes == 0)
    return 0;

  nl = memrchr (buf, buf + n_bytes, '\n');
  bol = (nl == NULL ? buf : nl + 1);

  /* If the last line of the input file has no terminating newline,
     treat it as a special case.  */
  if (bol < buf + n_bytes)
    {
      /* Print out the line from bol to end of input.  */
      fwrite (bol, 1, (buf + n_bytes) - bol, out);

      /* Add a newline here.  Otherwise, the first and second lines
	 of output would appear to have been joined.  */
      fputc ('\n', out);
    }

  while ((nl = memrchr (buf, bol - 1, '\n')) != NULL)
    {
      /* Output the line (which includes a trailing newline)
	 from NL+1 to BOL-1.  */
      fwrite (nl + 1, 1, bol - (nl + 1), out);

      bol = nl + 1;
    }

  /* If there's anything left, output the last line: BUF .. BOL-1.
     When the first byte of the input is a newline, there is nothing
     left to do here.  */
  if (buf < bol)
    fwrite (buf, 1, bol - buf, out);

  /* FIXME: this is work in progress.... */
  return ferror (out);
}

/* FIXME: describe */

static int
tac_stdin_to_mem (void)
{
  char *buf = NULL;
  size_t bufsiz = 8 * BUFSIZ;
  size_t delta = 8 * BUFSIZ;
  size_t n_bytes = 0;

  while (1)
    {
      ssize_t bytes_read;
      if (buf == NULL)
	buf = (char *) malloc (bufsiz);
      else
	buf = (char *) realloc (buf, bufsiz);

      if (buf == NULL)
	{
	  /* Free the buffer and fall back on the code that relies on a
	     temporary file.  */
	  free (buf);
	  /* FIXME */
	  abort ();
	}
      bytes_read = safe_read (STDIN_FILENO, buf + n_bytes, bufsiz - n_bytes);
      if (bytes_read == 0)
	break;
      if (bytes_read < 0)
	error (EXIT_FAILURE, errno, _("stdin: read error"));
      n_bytes += bytes_read;

      bufsiz += delta;
    }

  tac_mem (buf, n_bytes, stdout);

  return 0;
}
#endif

int
main (int argc, char **argv)
{
  const char *error_message;	/* Return value from re_compile_pattern. */
  int optc, errors;
  int have_read_stdin = 0;

  program_name = argv[0];
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);

  atexit (close_stdout);

  errors = 0;
  separator = "\n";
  sentinel_length = 1;
  separator_ends_record = 1;

  while ((optc = getopt_long (argc, argv, "brs:", longopts, NULL)) != -1)
    {
      switch (optc)
	{
	case 0:
	  break;
	case 'b':
	  separator_ends_record = 0;
	  break;
	case 'r':
	  sentinel_length = 0;
	  break;
	case 's':
	  separator = optarg;
	  if (*separator == 0)
	    error (EXIT_FAILURE, 0, _("separator cannot be empty"));
	  break;
	case_GETOPT_HELP_CHAR;
	case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
	default:
	  usage (1);
	}
    }

  if (sentinel_length == 0)
    {
      compiled_separator.allocated = 100;
      compiled_separator.buffer = (unsigned char *)
	xmalloc (compiled_separator.allocated);
      compiled_separator.fastmap = xmalloc (256);
      compiled_separator.translate = 0;
      error_message = re_compile_pattern (separator, strlen (separator),
					  &compiled_separator);
      if (error_message)
	error (EXIT_FAILURE, 0, "%s", error_message);
    }
  else
    match_length = sentinel_length = strlen (separator);

  read_size = INITIAL_READSIZE;
  /* A precaution that will probably never be needed. */
  while (sentinel_length * 2 >= read_size)
    read_size *= 2;
  G_buffer_size = read_size * 2 + sentinel_length + 2;
  G_buffer = xmalloc (G_buffer_size);
  if (sentinel_length)
    {
      strcpy (G_buffer, separator);
      G_buffer += sentinel_length;
    }
  else
    {
      ++G_buffer;
    }

  if (optind == argc)
    {
      have_read_stdin = 1;
      /* We need binary I/O, since `tac' relies
	 on `lseek' and byte counts.  */
      SET_BINARY2 (STDIN_FILENO, STDOUT_FILENO);
      errors = tac_stdin ();
    }
  else
    {
      for (; optind < argc; ++optind)
	{
	  if (STREQ (argv[optind], "-"))
	    {
	      have_read_stdin = 1;
	      SET_BINARY2 (STDIN_FILENO, STDOUT_FILENO);
	      errors |= tac_stdin ();
	    }
	  else
	    {
	      /* Binary output will leave the lines' ends (NL or
		 CR/LF) intact when the output is a disk file.
		 Writing a file with CR/LF pairs at end of lines in
		 text mode has no visible effect on console output,
		 since two CRs in a row are just like one CR.  */
	      SET_BINARY (STDOUT_FILENO);
	      errors |= tac_file (argv[optind]);
	    }
	}
    }

  /* Flush the output buffer. */
  output ((char *) NULL, (char *) NULL);

  if (have_read_stdin && close (0) < 0)
    error (EXIT_FAILURE, errno, "-");
  exit (errors == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
}