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Re: [PATCHES] Bootstrap: Allow user overriding of $AUTOCONF and $PERL.

From: Eric Blake
Subject: Re: [PATCHES] Bootstrap: Allow user overriding of $AUTOCONF and $PERL.
Date: Tue, 27 Jul 2010 15:15:56 -0600
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On 07/27/2010 03:08 PM, Eric Blake wrote:
> On 07/27/2010 02:58 PM, Stefano Lattarini wrote:
>> +# Let user choose which version of autoconf to use.
>> +AUTOCONF=${AUTOCONF-autoconf}
>> +
> I'm used to this variant, with less typing:
> : ${AUTOCONF=autoconf}
> But your way works, too.

Huh, I just realized that:

: ${var=val}

might be less efficient, if $var is already defined and contains
globbing characters.  To avoid wasting time on (unnecessary) file name
expansion, it is faster to use

: "${var=val}"

even though both variants should (normally) have the same end result.

In particular, on cygwin, doing globs can cause a side effect - if you
ever cause a glob() to take place on a string containing a backslash,
cygwin will warn on the console (but thankfully not pollute stderr)
about your potential use of non-POSIX filenames.  The bash-completion
package applied several patches earlier this year to avoid globs, in
part because of that cygwin side-effect.  I should probably document
that in the autoconf manual.

Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library

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