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Re: extension of file-test primitives?

From: dethrophes
Subject: Re: extension of file-test primitives?
Date: Wed, 23 Aug 2017 16:58:08 +0200
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Am 23.08.2017 um 16:46 schrieb Greg Wooledge:
On Wed, Aug 23, 2017 at 04:24:55PM +0200, Dethrophes wrote:
Which I always understood as the correct way of doing this in the
first place...

It's not as good as multiple test commands: test -f file && test -x
There's no ambiguity and you get short-circuiting.
Only if you are using the test built-in, otherwise the latter means 2 
spawns/forks however the shell in question calls the test exec.
The comparison was against "test -f file -a -x file" which is deprecated.
The use of "-a" as a logical AND is not mandated by POSIX except in
"obsolescent XSI" mode.


So if you're using test ... -a ... then you're almost certainly relying
on test being bash's builtin version.  And since this is bug-bash, we
generally assume you are using bash.

There is also test(1) in GNU coreutils, which currently still supports
the binary -a, but the coreutils 8.26 man page says "NOTE:  Binary  -a
and -o are inherently ambiguous.  Use 'test EXPR1 && test EXPR2' or
'test EXPR1 || test EXPR2' instead."

But, writing a script that relies on test being the one provided by
GNU coreutils (or any other version which implements the obsolescent
XSI deprecated feature set) is also extremely silly.
Ok I wasn't aware of that it is depricated.
Having said that it is pretty widely supported. I make use of this in pdksh, bash, dash, ksh and in a couple of test implementations not just the gnu one.

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