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From: John Baldwin <jhb@freebsd.org>
To: Yar Tikhiy <yar@freebsd.org>
Date: Thu, 27 Jul 2006 15:34:57 -0400
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Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org
Subject: Re: cvs commit: src/bin/test test.1
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On Thursday 27 July 2006 15:08, Yar Tikhiy wrote:
> yar 2006-07-27 19:08:21 UTC
>
> FreeBSD src repository
>
> Modified files:
> bin/test test.1
> Log:
> Document that both sides of -a or -o are always evaluated. This
> "feature" doesn't seem to be in the standards or elsewhere, and
> it is against what we are used to in C and sh(1), so put the
> paragraph under BUGS.
>
> Pointed out by: dougb
> MFC after: 3 days
This isn't a bug, it's the only way it can work. What you are missing is that
the shell has to evaluate the arguments and then pass them to test(1). Thus,
when you do:
if [ foo ] && [ bar ]; then
...
fi
The shell runs evaluates all of '[ foo ]' as needed and runs it. It then
decides whether to evaluate and run '[ bar ]' after the first command runs.
When you do:
if [ foo -a bar ]; then
...
fi
The shell has to evaluate all of '[ foo -a bar ]' and run the single command
and make the decision based on what it returns.
I don't think this is really a bug, it's more the fact of realizing that even
if [ maybe optimized to be a built-in, when you are using it, you have to
treat it as the shell executing a separate program, just as you would expect:
if grep -q ${FOO} < ${BAR}; then
...
fi
To evaluate both ${FOO} and ${BAR} before running grep.
--
John Baldwin