A demonstration is better than many words:

#!/usr/bin/perl -w

use strict;
use Getopt::Long;

my $targ    = 'localhost';
my $firstport    = 1;
my $lastport    = 1024;
my $proto    = 'tcp';
my $udptimeout    = 3;
my $contimeout    = 3;

{
  my %options;
  GetOptions(\%options, qw(targ=s firstport=s lastport=s proto=s udpti
+meout=s contimeout=s help!));

  if (defined $options{help}){
    Usage('You rang, sir?');
    exit;
  }

  ($targ, $firstport, $lastport, $proto, $udptimeout, $contimeout) =
  @options{qw(targ firstport lastport proto udptimeout contimeout)};
}
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With some further generalization the variable-/option-names wouldn't have to appear four times each as in this code either.

Update: maybe you want qw(targ=s firstport=s lastport=s proto=s udptimeout=i contimeout=i help!)? I can see someone saying POP3 for the port f.ex - but it doesn't seem to make any sense to take arbitrary values for the timeout parameters.

Makeshifts last the longest.