Re: diff: incorrect and undocumented cmp output when stdout is redirected

[Paul Eggert]

On second thought I have installed this patch instead, as it's simpler
and a tad more efficient in the usual case:

2006-03-09  Paul Eggert  <address@hidden>

        * src/cmp.c (type_no_stdout): New constant.
        (main): Use it to avoid bug when the "EOF on foo" message is
        generated and stdout is /dev/null.
        Problem reported by Vincent Lefevre (Debian bug 356083).

--- cmp.c       5 Jan 2006 07:23:55 -0000       1.39
+++ cmp.c       9 Mar 2006 20:54:39 -0000       1.41
@@ -78,6 +78,7 @@ static enum comparison_type
   {
     type_first_diff,   /* Print the first difference.  */
     type_all_diffs,    /* Print all differences.  */
+    type_no_stdout,    /* Do not output to stdout; only stderr.  */
     type_status                /* Exit status only.  */
   } comparison_type;
 
@@ -317,7 +318,7 @@ main (int argc, char **argv)
       if (fstat (STDOUT_FILENO, &outstat) == 0
          && stat (NULL_DEVICE, &nullstat) == 0
          && 0 < same_file (&outstat, &nullstat))
-       comparison_type = type_status;
+       comparison_type = type_no_stdout;
     }
 
   /* If only a return code is needed,
@@ -356,7 +357,7 @@ main (int argc, char **argv)
   for (f = 0; f < 2; f++)
     if (close (file_desc[f]) != 0)
       error (EXIT_TROUBLE, errno, "%s", file[f]);
-  if (exit_status != 0  &&  comparison_type != type_status)
+  if (exit_status != EXIT_SUCCESS && comparison_type < type_no_stdout)
     check_stdout ();
   exit (exit_status);
   return exit_status;
@@ -536,6 +537,9 @@ cmp (void)
              while (first_diff < smaller);
              ret = EXIT_FAILURE;
              break;
+
+           case type_no_stdout:
+             break;
            }
        }