#!/usr/bin/perl 
$array=undef;
warn "array ",defined($array) ? 'is' : 'is not'," defined";
warn '$#{$array} is ',$#{$array};
warn "array ",defined($array) ? 'is' : 'is not'," defined";

##</code><code>##

array is not defined at /home/smitty/bat/t line 3.
$#{$array} is -1 at /home/smitty/bat/t line 4.
array is defined at /home/smitty/bat/t line 5.