Command line options with Perl: EG

#!/usr/bin/perl
use strict;
use warnings;
use Getopt::Std;
use vars qw/ %opts /;

getopts('he:c:', \%opts );
usage() if $opts{h};
usage() if($opts{e} eq "" or $opts{c} eq "");

sub usage(){
print "This program should be used as below\n";
print "usage: $0 [-h] [e petrol] [-c elgi]\n";
print " -h : this (help) message\n";
print " -e : energy name\n";
print " -c : compressor name\n";
print " example: $0 -e petrol -c elgi\n";
exit;
}