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Re: builtin test command file existence fails with negation

From: Andreas Schwab
Subject: Re: builtin test command file existence fails with negation
Date: Tue, 21 Jul 2009 17:53:54 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.96 (gnu/linux)

Lynn Kerby <lfk@kerbit.net> writes:

>       Use of the '-a' option to the builtin test command fails to
>       produce the correct result when used with negation. The specific
>       error the case where the file exists and a "test ! -a file" is
>       executed.  If the script is changed to use '-e' for file
>       existence the result is correct as expected.  If the script is
>       modified to place parenthesis around the '-a file' expression,
>       the result is also correct.

This is not a bug, but consistent with the POSIX rules.  Better avoid
the (nonstandard) -a unary operator and use -e instead.  The problem is
that -a is also a binary operator, and POSIX says that if test is called
with three arguments and the second argument is a binary operator it
should be parsed as such.

for details.


Andreas Schwab, schwab@linux-m68k.org
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