md5sum,sha*sum: add --ignore-missing for checking a subset of files

* doc/coreutils.texi (md5sum invocation): Document the new option.
* src/md5sum.c (digest_file): Return an empty digest to indicate
a missing file.
(digest_check): Don't fail or output status given an empty checksum.
(usage): Document the new option.
(main): Process and validate the new option.
* tests/misc/md5sum.pl: Add new test cases.
* NEWS: Mention the new feature.
Fixes http://bugs.gnu.org/15604

1 files changed, 32 insertions, 2 deletions

diff --git a/src/md5sum.c b/src/md5sum.c
index 5d4b958ee..49da8edc4 100644
--- a/src/md5sum.c
+++ b/src/md5sum.c
@@ -119,6 +119,9 @@ static bool status_only = false;
    improperly formatted checksum line.  */
 static bool warn = false;
 
+/* With --check, ignore missing files.  */
+static bool ignore_missing = false;
+
 /* With --check, suppress the "OK" printed for each verified file.  */
 static bool quiet = false;
 
@@ -133,7 +136,8 @@ static int bsd_reversed = -1;
    non-character as a pseudo short option, starting with CHAR_MAX + 1.  */
 enum
 {
-  STATUS_OPTION = CHAR_MAX + 1,
+  IGNORE_MISSING_OPTION = CHAR_MAX + 1,
+  STATUS_OPTION,
   QUIET_OPTION,
   STRICT_OPTION,
   TAG_OPTION
@@ -143,6 +147,7 @@ static struct option const long_options[] =
 {
   { "binary", no_argument, NULL, 'b' },
   { "check", no_argument, NULL, 'c' },
+  { "ignore-missing", no_argument, NULL, IGNORE_MISSING_OPTION},
   { "quiet", no_argument, NULL, QUIET_OPTION },
   { "status", no_argument, NULL, STATUS_OPTION },
   { "text", no_argument, NULL, 't' },
@@ -197,7 +202,8 @@ Print or check %s (%d-bit) checksums.\n\
 "), stdout);
       fputs (_("\
 \n\
-The following four options are useful only when verifying checksums:\n\
+The following five options are useful only when verifying checksums:\n\
+      --ignore-missing  don't fail or report status for missing files\n\
       --quiet          don't print OK for each successfully verified file\n\
       --status         don't output anything, status code shows success\n\
       --strict         exit non-zero for improperly formatted checksum lines\n\
@@ -482,6 +488,11 @@ digest_file (const char *filename, int *binary, unsigned char *bin_result)
       fp = fopen (filename, (O_BINARY && *binary ? "rb" : "r"));
       if (fp == NULL)
         {
+          if (ignore_missing && errno == ENOENT)
+            {
+              *bin_result = '\0';
+              return true;
+            }
           error (0, errno, "%s", quotef (filename));
           return false;
         }
@@ -597,6 +608,7 @@ digest_check (const char *checkfile_name)
 
           ++n_properly_formatted_lines;
 
+          *bin_buffer = '\1'; /* flag set to 0 for ignored missing files.  */
           ok = digest_file (filename, &binary, bin_buffer);
 
           if (!ok)
@@ -610,10 +622,17 @@ digest_check (const char *checkfile_name)
                   printf (": %s\n", _("FAILED open or read"));
                 }
             }
+          else if (ignore_missing && ! *bin_buffer)
+            {
+              /* Treat an empty buffer as meaning a missing file,
+                 which is ignored with --ignore-missing.  */
+              ;
+            }
           else
             {
               size_t digest_bin_bytes = digest_hex_bytes / 2;
               size_t cnt;
+
               /* Compare generated binary number with text representation
                  in check file.  Ignore case of hex digits.  */
               for (cnt = 0; cnt < digest_bin_bytes; ++cnt)
@@ -749,6 +768,9 @@ main (int argc, char **argv)
         warn = true;
         quiet = false;
         break;
+      case IGNORE_MISSING_OPTION:
+        ignore_missing = true;
+        break;
       case QUIET_OPTION:
         status_only = false;
         warn = false;
@@ -795,6 +817,14 @@ main (int argc, char **argv)
       usage (EXIT_FAILURE);
     }
 
+  if (ignore_missing && !do_check)
+    {
+      error (0, 0,
+             _("the --ignore-missing option is meaningful only when "
+               "verifying checksums"));
+      usage (EXIT_FAILURE);
+    }
+
   if (status_only && !do_check)
     {
       error (0, 0,