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Test existence of shell variable, bash, csh

This came up on another list.  The problem involves testing existence of
a Unix shell variable from another program with limited system
interaction features.

I usually write this in bash as:

    if [ x${MYVAR} = x ]; then
        echo 'MYVAR doesn't exist (or isn't set)'
	else echo "MYVAR exists, value: $MYVAR"

...which essentially checks whether or not the variable has a non-null
value.  But would report that $MYVAR doesn't exist if in fact it was set
equal to "".

In contrast, csh and derivatives have:


...which allows testing of presence of a variable.

...but I'm not aware of a similar bash/korn/bourne feature.  Anyone?

Karsten M. Self <kmself@ix.netcom.com>    http://kmself.home.netcom.com/
 What part of "Gestalt" don't you understand?       There is no K5 cabal
  http://gestalt-system.sourceforge.net/         http://www.kuro5hin.org

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