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From: Mel <fbsd.questions@rachie.is-a-geek.net>
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Date: Thu, 10 Jul 2008 14:15:51 +0200
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Cc: Anton Shterenlikht <mexas@bristol.ac.uk>
Subject: Re: snippet of configure script - explain please
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On Thursday 10 July 2008 06:24:46 Malcolm Kay wrote:

> >    9255 if { as_var=$as_ac_var; eval "test \"\${$as_var+set}\" = set"; };
> > then
>
> I find this line somewhat strange as I've not been able
> to find documentation for the expansion of ${parameter+set} under the
> Bourne shell. (nor bash, nor ksh)
> *****************************************************
> Presumably someone out there knows where to find it?
> *****************************************************

It's shorthand for ${paramter:+set}, so if unset, you get "", otherwise you 
get "set":
$ echo ${foo+set}

$ echo ${HOME+set}
set


-- 
Mel

Problem with today's modular software: they start with the modules
    and never get to the software part.