Re: unset FOO

[Eric Blake]

Peter Seebach <seebs <at> seebs.net> writes:

> >> ${FOO+unset FOO}
> >> 
> >No, it does NOT work in Solaris sh (tested on Solaris 8):
> >
> I think it needs to be in quotes, as with other {x+a b} expansions.

Quotes won't help; the shell then tries to evaluate the command 'unset FOO' 
with no arguments, because there is no reason to do IFS splitting.

>  I may
> have tested it in double quotes or something.  Or I may just have been
> confused.

But this works, using an intermediate variable, so that IFS splitting still 
occurs:

$ /bin/sh -c 'foo=a;tmp="unset foo";${foo+$tmp};echo ${foo+set}'; echo $?

0
$

But why waste the time going through a temporary variable, when you can use:

test ${foo+set} = set && unset foo

-- 
Eric Blake