bug#34347: At least add 2nd comm error message after output

[Pádraig Brady]

On 06/02/19 04:16, 積丹尼 Dan Jacobson wrote:
> (info "(coreutils) comm invocation")
> 
> "Before ‘comm’ can be used, the input files must be sorted"
>                                              ^^^^
> "If an input file is diagnosed as being unsorted, the ‘comm’ command
> will exit with a nonzero status (and the output should not be used).
>                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> "Forcing ‘comm’ to process wrongly sorted input files ... is not
> guaranteed to produce any particular output. The output will probably
> not correspond with whatever you hoped it would be."
> 
> OK, so I would change the default.
> 
> The new default should be: before producing even a line of output,
> check both files. If either of them is in order, print the error
> message, and exit non-zero... _without any line of output!_
> 
> Because currently,
> 
> $ seq 55 > 5
> $ seq 55 |tac > 5r
> $ comm 5 5r
> just causes the error messages to fly off the screen, leaving only the
> savvy user, who checks exit values, to have any inkling that there is a
> problem, and he should not order futher warships, airplanes, etc. based
> on the results after all.
> 
> OR, be so kind as to add a second error message after all the output is
> printed, so it won't fly off the screen.

This is a fair point.
Note the --check-order option is stricter and will exit upon the first error 
message.
join has the same considerations, so this should handle both:

cheers,
Pádraig

diff --git a/src/comm.c b/src/comm.c
index da8d5cf..6f46c98 100644
--- a/src/comm.c
+++ b/src/comm.c
@@ -493,7 +493,7 @@ main (int argc, char **argv)
   compare_files (argv + optind);

   if (issued_disorder_warning[0] || issued_disorder_warning[1])
-    return EXIT_FAILURE;
+    error (EXIT_FAILURE, 0, _("input is not in sorted order"));
   else
     return EXIT_SUCCESS;
 }
diff --git a/src/join.c b/src/join.c
index 7c75c76..e2ba02b 100644
--- a/src/join.c
+++ b/src/join.c
@@ -1193,7 +1193,7 @@ main (int argc, char **argv)
     die (EXIT_FAILURE, errno, "%s", quotef (g_names[1]));

   if (issued_disorder_warning[0] || issued_disorder_warning[1])
-    return EXIT_FAILURE;
+    error (EXIT_FAILURE, 0, _("input is not in sorted order"));
   else
     return EXIT_SUCCESS;
 }