GNU bug report logs - #18449
"cat x >> x" error even when x is empty

Previous Next

Full log

View this message in rfc822 format

From: Vincent Lefevre <vincent <at> vinc17.net>
To: 18449 <at> debbugs.gnu.org
Subject: bug#18449: "cat x >> x" error even when x is empty
Date: Thu, 11 Sep 2014 15:00:44 +0200

With coreutils 8.23 under Debian/unstable:

ypig% : > x
ypig% cat x >> x
cat: x: input file is output file
ypig% POSIXLY_CORRECT=1 cat x >> x
cat: x: input file is output file

while there's no reason to return an error in this case: the file
should just remain empty. Using the same file for input and output
isn't disallowed by POSIX, AFAIK.

This may not seem really useful here, but this can potentially break
scripts with things like:

  cat "$foo" >> "$bar"

where "$foo" may be the same file as "$bar" only if it is empty.

BTW, when x isn't empty, I wonder whether an error is correct if
POSIXLY_CORRECT is set. The result will typically depend on the
implementation and possibly be non-deterministic, but POSIX doesn't
seem to allow an error (except FS errors, such as disk full).

-- 
Vincent Lefèvre <vincent <at> vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.