#!/usr/bin/perl 
 
use strict; 
use warnings; 
 
# See `perldoc English` 
use English qw( -no_match_vars ) ;  # Avoids regex performance penalty 
 
use Data::Dumper; 
# Make Data::Dumper pretty 
$Data::Dumper::Sortkeys = 1; 
$Data::Dumper::Indent   = 1; 
$Data::Dumper::Maxdepth = 0; 
 
my $var = !0; 
print Dumper \$var; 
 
$var = !1; 
print Dumper \$var;