GNU bug report logs - #18402
Wrong output for single character files without newline

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#18402: closed (Wrong output for single character files
 without newline)
Date: Wed, 03 Sep 2014 23:07:02 +0000

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Your message dated Wed, 03 Sep 2014 16:05:55 -0700
with message-id <54079ED3.8050402 <at> cs.ucla.edu>
and subject line Re: [bug-diffutils] bug#18402: Wrong output for single character files without newline
has caused the debbugs.gnu.org bug report #18402,
regarding Wrong output for single character files without newline
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


-- 
18402: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=18402
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Contact help-debbugs <at> gnu.org with problems

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From: Eric Blake <eblake <at> redhat.com>
To: Navin Kabra <navin <at> smriti.com>, bug-gnu-utils <at> gnu.org,
 bug-diffutils <at> gnu.org
Subject: Re: Wrong output for single character files without newline
Date: Wed, 03 Sep 2014 15:03:44 -0600

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[adding bug-diffutils, as requested by diff --help]

On 09/03/2014 04:17 AM, Navin Kabra wrote:
> Consider this:
> 
>     echo -n a > /tmp/a
>     echo -n b > /tmp/b
>     diff -B /tmp/a /tmp/b

'echo -n' is non-portable.  Please get used to using 'printf' instead.

> 
> Clearly, the two files are different, yet, diff seems to think that the
> files are identical. I've managed to reproduce this problem on Ubuntu
> 14.04 with diffutils 3.3, on CloudLinux 5.10 with diffutils 2.8.1, and
> also Ubuntu 10.04 with diffutils 2.8.1.
> 
> If I don't use the -B option, the problem goes away. If the files do end
> with a newline, the problem goes away. If the files contain more than 1
> character, the problem goes away. If combined with *some* of the other
> options (e.g. -e or -y) the problem goes away.

Actually, I couldn't reproduce -y making the problem go away:

$ ./src/diff -By <(printf a) <(printf b)
a								b
$ echo $?
0

Thanks for the extensive analysis; I can confirm that this bug is still
present in the latest diffutils.git sources, although I have not
personally hunted for the culprit line of code yet.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Eric Blake <eblake <at> redhat.com>, navin <at> smriti.com, 
 Matt Johnson <mj1856 <at> hotmail.com>, 18402-done <at> debbugs.gnu.org
Subject: Re: [bug-diffutils] bug#18402: Wrong output for single character
 files without newline
Date: Wed, 03 Sep 2014 16:05:55 -0700

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Thanks for reporting that.  I installed the attached 3 patches; patch #2 
should fix the bug.

[0001-diff-fix-performance-bug-with-prefix-computation.patch (text/plain, attachment)]

[0002-diff-fix-bug-with-diff-B-and-incomplete-lines.patch (text/plain, attachment)]

[0003-doc-mention-diff-B-fix-in-NEWS.patch (text/plain, attachment)]

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