#!/usr/bin/perl
use warnings;

my($str,$empty_str,$number,$number_zero)=('Hi','',1,0);


if($str!=undef){print"\$str is defined\n"}  
if($empty_str!=undef){print"\$empty_str is defined\n"}
if($number!=undef){print"\$number is defined\n"}
if($number_zero!=undef){print"\$number_zero is defined\n"}