Re: [PLUG] Distinguishing between environment variable with null value and one that is not set

[sean finney <seanius@seanius.net>]

On Tue, Oct 13, 2009 at 05:19:26PM -0400, Paul L. Snyder wrote:
> How about this, which should be POSIX-compliant (and doesn't require a
> subshell):
> 
>   % foo=bar
>   % if [[ -z ${foo+isset} ]]; then echo nope; else echo yep; fi
>   yep
>   % foo=''
>   % if [[ -z ${foo+isset} ]]; then echo nope; else echo yep; fi
>   yep
>   % unset foo
>   % if [[ -z ${foo+isset} ]]; then echo nope; else echo yep; fi
>   nope
> 
> 'isset' doesn't matter, it could be any non-zero-length string.

i hate to tell ya, but i'm pretty sure "[[" is also non-posix :)

if in doubt, install ksh, dash, and posh.  they are forgiving in
approximately descending order :)


	sean

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