wdiff does not work correctly with <() redirection

[Thomas Bleher]

Binary package hint: wdiff

wdiff produces a diff but does not display all information if one or both of the files given is a bash process substitution.

An example session:
$ echo "word1 word2 word3" > file1
$ echo "word1 word4 word3" > file2
$ wdiff file1 file2
word1 [-word2-] {+word4+} word3
$ wdiff <(cat file1) <(cat file2)
[--]{++}$ wdiff file1 <(cat file2)
 [-word2-]{++}$ wdiff <(cat file1) file2
word1[--] {+word4+} word3
$ bash --version
GNU bash, version 3.2.25(1)-release (x86_64-pc-linux-gnu)
Copyright (C) 2005 Free Software Foundation, Inc.
$ wdiff --version
GNU wdiff 0.5
Copyright (C) 1992 Free Software Foundation, Inc.

ProblemType: Bug
Architecture: amd64
Date: Thu Nov 8 11:16:56 2007
Dependencies:
 libgcc1 1:4.2.1-5ubuntu4
 gcc-4.2-base 4.2.1-5ubuntu4
 libncurses5 5.6+20070716-1ubuntu3
 libc6 2.6.1-1ubuntu10
DistroRelease: Ubuntu 7.10
Package: wdiff 0.5-17build1
PackageArchitecture: amd64
SourcePackage: wdiff
Uname: Linux thomas 2.6.24-rc2 #8 SMP Wed Nov 7 09:38:01 CET 2007 x86_64 GNU/Linux

[Thomas Bleher (tbleher)]

A small addition: While it would be nice if wdiff supported <(), failing is OK IMHO as long as there is some error message. I just used wdiff for the first time and was confused why it didn't properly display deleted words. Only after some searching it became clear that it was because I had piped in the old file through <().

[Rory McCann (rorymcc)]

The strace for it is interesting. It looks like wdiff does a stat on the files and the result returns is 0.

strace -efile wdiff -1 <(echo -e "line1\nline2") <(echo -e "line1\nline3")
execve("/usr/bin/wdiff", ["wdiff", "-1", "/dev/fd/63", "/dev/fd/62"], [/* 44 vars */]) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/libncurses.so.5", O_RDONLY) = 3
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/tls/i686/cmov/libc.so.6", O_RDONLY) = 3
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/tls/i686/cmov/libdl.so.2", O_RDONLY) = 3
stat64("/dev/fd/63", {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
open("/dev/fd/63", O_RDONLY) = 3
open("/tmp/wdiff.bF8FQN", O_RDWR|O_CREAT|O_EXCL, 0600) = 4
stat64("/dev/fd/62", {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
open("/dev/fd/62", O_RDONLY) = 4
open("/tmp/wdiff.HqUIDm", O_RDWR|O_CREAT|O_EXCL, 0600) = 5
--- SIGCHLD (Child exited) @ 0 (0) ---
unlink("/tmp/wdiff.bF8FQN") = 0
unlink("/tmp/wdiff.HqUIDm") = 0
{++}Process 20780 detached

I suspect that's causing it to think the files are empty and not doing anything.

diff however does work for named pipes,
$ diff -u <(echo -e "line1\nline2") <(echo -e "line1\nline3")
--- /dev/fd/63 2009-03-30 12:17:43.235246354 +0100
+++ /dev/fd/62 2009-03-30 12:17:43.235246354 +0100
@@ -1,2 +1,2 @@
 line1
-line2
+line3

[xteejx (xteejx)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. The issue that you reported is one that should be reproducible with the development release - Karmic Koala. It would help us greatly if you could test with it so we can work on getting it fixed in the next release of Ubuntu. You can find out more about the development release at http://www.ubuntu.com/testing/. Thanks again and we appreciate your help.

[Thomas Bleher (tbleher)]

Can someone with a test machine please test this bug?
I don't have time currently to install Karmic Koala, so I can't say if this bug is still there.
But for anyone with a test machine, it should be trivial to reproduce the bug.

[Rory McCann (rorymcc)]

I have tested this on 9.10 Karmic Koala and the bug is still there for wdiff 0.5-18

However I have discovered another programme dwdiff that is similar to wdiff and *does* work with bash process direction. As a work around people can use this other programme instead.

[xteejx (xteejx)]

Thank you for updating us with this. Marking Confirmed.

[Johan Euphrosine (proppy)]

dwdiff in universe does not have this issue.

It looks fixed upstream thought:
http://savannah.gnu.org/bugs/?25883

[Martin von Gagern (gagern)]

Fix committed but not released yet. Pre-release available at http://alpha.gnu.org/gnu/wdiff/ and final release expected this month.

[xteejx (xteejx)]

I assume this was fixed in the release that came with Maverick. If this is incorrect please set this bug back to New. Thank you.