#!/usr/local/bin/perl -l

use strict;

foreach (0,'',undef) {
   print "'$_' is zero number" if $_ == 0;
   print "'$_' is zero string" if $_ eq '0';
   print "'$_' is empty string" if $_ =~ /^$/;
   print "'$_' is empty string" if $_ eq '';
   print "'$_' is undef" if ! defined $_;
}