Re: Test existence of shell variable, bash, csh

[dmaziuk@bmrb.wisc.edu (Dimitri Maziuk)]

On Sat, May 05, 2001 at 02:34:47PM -0700, Karsten M. Self wrote:
> This came up on another list.  The problem involves testing existence of
> a Unix shell variable from another program with limited system
> interaction features.
...
>    $?MYVAR
> 
> ...which allows testing of presence of a variable.
> 
> ...but I'm not aware of a similar bash/korn/bourne feature.  Anyone?

Just as a side note: 'setenv MYVAR "/path:$MYVAR"' will fail in [t]csh
if MYVAR is not defined, hence constructs like

if ( $?MYVAR ) then
    setenv MYVAR "/usr/local/myprog:$MYVAR"
else
    setenv MYVAR "/usr/local/myprog"
endif

Bash will quite happily expand an undefined variable to a null string,
so the test above is not needed at all:

export MYVAR="/path:$MYVAR"

is all you need.

Dima
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