Prevent certain command lines from inadvertantly overwriting the output file.

Declare copy buffer (tmp)

Variable declaration

Notes

This declarative segment is simply misplaced. It should be part of the main body of code. Perhaps this used to be a shared with other capabilities.

The buffer is use to hold a chunk of file while it is being copied to an temporary location.

Segment Source

1722:   char *minus = "-", *outfile = minus, **files, *tmp;

Copy any overwritten input file to a temporary

Code insertion

Create a copy of every input file that might be the same file as the output file.

Segment Source

2064:   if (strcmp (outfile, "-"))
2065:     {
2066:       struct stat outstat;
2067:       if (stat (outfile, &outstat) == 0)
2068:         {
2069:           /* The following code prevents a race condition when
2070:              people use the brain dead shell programming idiom:
2071:                   cat file | sort -o file
2072:              This feature is provided for historical compatibility,
2073:              but we strongly discourage ever relying on this in
2074:              new shell programs. */
2075: 
2076:           /* Temporarily copy each input file that might be another name
2077:              for the output file.  When in doubt (e.g. a pipe), copy.  */
2078:           for (i = 0; i < nfiles; ++i)
2079:             {
2080:               char buf[8192];
2081:               FILE *fp;
2082:               int cc;
2083: 
2084:               if (S_ISREG (outstat.st_mode) && strcmp (outfile, files[i]))
2085:                 {
2086:                   struct stat instat;
2087:                   if ((strcmp (files[i], "-")
2088:                        ? stat (files[i], &instat)
2089:                        : fstat (STDIN_FILENO, &instat)) != 0)
2090:                     {
2091:                       error (0, errno, "%s", files[i]);
2092:                       cleanup ();
2093:                       exit (SORT_FAILURE);
2094:                     }
2095:                   if (S_ISREG (instat.st_mode)
2096:                       && (instat.st_ino != outstat.st_ino
2097:                           || instat.st_dev != outstat.st_dev))
2098:                     {
2099:                       /* We know the files are distinct.  */
2100:                       continue;
2101:                     }
2102:                 }
2103: 
2104:               fp = xfopen (files[i], "r");
2105:               tmp = tempname ();
2106:               ofp = xtmpfopen (tmp);
2107:               while ((cc = fread (buf, 1, sizeof buf, fp)) > 0)
2108:                 write_bytes (buf, cc, ofp);
2109:               if (ferror (fp))
2110:                 {
2111:                   error (0, errno, "%s", files[i]);
2112:                   cleanup ();
2113:                   exit (SORT_FAILURE);
2114:                 }
2115:               xfclose (ofp);
2116:               xfclose (fp);
2117:               files[i] = tmp;
2118:             }
2119:         }