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

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From: Eric Blake <eblake <at> redhat.com>
To: navin <at> smriti.com, bug-gnu-utils <at> gnu.org, 18402 <at> debbugs.gnu.org
Subject: bug#18402: Wrong output for single character files without newline
Date: Wed, 03 Sep 2014 15:03:44 -0600

[Message part 1 (text/plain, inline)]

[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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