#!/usr/bin/perl -w

use strict;

my $str;
printf "\$str is %s\n", defined $str ? $str : "<undefined>";

$str = "Hello";
printf "\$str is %s\n", defined $str ? $str : "<undefined>";

$str = undef;
printf "\$str is %s\n", defined $str ? $str : "<undefined>";

$str++;
printf "\$str is %s\n", defined $str ? $str : "<undefined>";