./program.pl -a param1 param2 -b param3 param4

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;

use Getopt::Long;

my %options = ();

GetOptions (
             "a=s" => \$options{'a'},
             "b=s" => \$options{'b'},
             "z!"  => \$options{'z'},
            );

my %Subs = (
             'a' => \&do_a,
             'b' => \&do_b,
             'z' => \&do_z,
            );

while (my ($sub_name, $function) = each %Subs){
    $function->($options{$sub_name});
}

sub do_a {
  my $active = shift;
  return unless $active;
  
  my $param1 = $active;
#  my $param2 = shift @ARGV;
#  print "$param1, $param2, \n";
}

sub do_b {
  my $active = shift;
  return unless $active;
  
  my $param1 = $active;
#  my $param2 = shift @ARGV;
#  print "$param1, $param2, \n";

}

sub do_z {
  my $active = shift;
  return unless $active;
  
  #do stuff without parameters
}
##</code><code>##

my $param2 = shift @ARGV; #commented out in the code above

##</code><code>##

$perl program.pl -a param1_a param2_a -b param1_b param2_b

param1_a, param2_a, 
param1_b, param2_b, 

##</code><code>##

$perl program.pl -b param1_b param2_b -a param1_a param2_a

param1_a, param2_b, 
param1_b, param2_a,