GNU bug report logs - #34347
comm: add 2nd error message after output

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
To: bug-coreutils <at> gnu.org
Subject: At least add 2nd comm error message after output
Date: Wed, 06 Feb 2019 20:16:21 +0800

(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.

Message #14 received at 34347-done <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>,
 34347-done <at> debbugs.gnu.org
Subject: Re: bug#34347: At least add 2nd comm error message after output
Date: Sat, 9 Feb 2019 11:20:49 -0800

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;
 }

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