#!/usr/bin/perl

use strict;
use warnings;

use Getopt::Long;

my %args;

GetOptions(\%args, 'adduser:s@');

use Data::Dumper; print Dumper(\%args);

##</code><code>##

$ perl ./a.pl
$VAR1 = {};
$ perl ./a.pl --adduser
$VAR1 = {
          'adduser' => [
                         ''
                       ]
        };
$ perl ./a.pl --adduser blah
$VAR1 = {
          'adduser' => [
                         'blah'
                       ]
        };