#!/usr/bin/perl

use strict;
use Getopt::Long;

GetOptions(
  'a=s' => \my $opt_a,
  'b=s' => \my $opt_b,
  ...
  'z=s' => \my $opt_z,
);

##</code><code>##


for my $i (<loop through all the options>) {
  die if ( ! $i );
}