Another usefull statement could be:

$x=Not $x

This will invert the value of a boolean value, from 0 to 1 or 1 to 0

When executed on a number <> 0, it returns 0
When executed on a not defined variable, it returns 1
When executed on an empty string, it returns 1
When executed on a string, it returns 0

-Erik

Edited by request from BrianTX [Embarrassed]
Original post stated:
When executed on a number <> 0, it returns 1

[ 12 June 2002, 00:11: Message edited by: kholm ]