#!/usr/bin/perl -l

# http://perlmonks.org/?node_id=1193761

use strict;
use warnings;

my @list1 = qw( a b c );
my @list2 = qw( 1 2 );

my $reverse = 0;
my @combinations = map { my $left = $_;
  map "$left $_", $reverse++ % 2 ? reverse @list2 : @list2 } @list1;

print for @combinations;