#!/usr/bin/perl -w
use strict;

my %hash;

$hash{'a'} = "alpha";
$hash{'b'} = "";
$hash{'c'} = undef;

print "a='" . $hash{'a'} . "'\n";
print "b='" . $hash{'b'} . "'\n";
print "c='" . $hash{'c'} . "'\n";
print "d='" . $hash{'d'} . "'\n\n";

print "exists(a)='" . exists($hash{'a'}) . "'\n";
print "exists(b)='" . exists($hash{'b'}) . "'\n";
print "exists(c)='" . exists($hash{'c'}) . "'\n";
print "exists(d)='" . exists($hash{'d'}) . "'\n\n";

print "defined(a)='" . defined($hash{'a'}) . "'\n";
print "defined(b)='" . defined($hash{'b'}) . "'\n";
print "defined(c)='" . defined($hash{'c'}) . "'\n";
print "defined(d)='" . defined($hash{'d'}) . "'\n\n";

print "a is true\n" if($hash{'a'});
print "b is true\n" if($hash{'b'});
print "c is true\n" if($hash{'c'});
print "d is true\n" if($hash{'d'});