#!/usr/local/bin/perl -w
use Getopt::Long;

my ($hello,$goodbye); # option switches
GetOptions (
    "hello"  => \$hello,
    "goodbye" => \$goodbye,
);

if ($hello) {
   print "Hello world\n";
}

if ($goodbye) {
    print "Goodbye!\n";
}

##</code><code>##

# use full options
> perl test.pl --hello --goodbye
Hello world
Goodbye!

##</code><code>##

# use abbreviation 
> perl test.pl -h
Hello world