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Re: Addendum: Possible Bug in comm ?
From: |
Paul Eggert |
Subject: |
Re: Addendum: Possible Bug in comm ? |
Date: |
Thu, 14 Sep 2006 10:45:13 -0700 |
User-agent: |
Gnus/5.1008 (Gnus v5.10.8) Emacs/21.4 (gnu/linux) |
"Joseph A. Wiencko, Jr." <address@hidden> writes:
> "there exists no collating sequence in which this should be the
> behavior of comm -- it is contrary to the basic, stated behavior of
> comm REGARDLESS OF THE COLLATING SEQUENCE".
This misunderstands the specification of comm. The coreutils
documentation says:
Before `comm' can be used, the input files must be sorted using the
collating sequence specified by the `LC_COLLATE' locale.
<http://www.gnu.org/software/coreutils/manual/html_mono/coreutils.html#comm-invocation>
The POSIX documentation says the same thing in a different way:
If the lines in both files are not ordered according to the
collating sequence of the current locale, the results are
unspecified.
<http://www.opengroup.org/onlinepubs/009695399/utilities/comm.html>
These specs make it clear that if you give `comm' unsorted input,
`comm' is entitled to do whatever it pleases (short of looping or
dumping core; the GNU coding standards wouldn't allow that). It
doesn't matter whether there is an alternative universe in which
the input was actually sorted.
Personally I think `comm' should print a diagnostic if the input is
unsorted. I'd welcome a patch along those lines, if it didn't slow
down `comm' too much in the normal case (that's the hard part :-).