for my $first (@group1) {
    for my $second (@group2) {
        for my $third (@group3) {
            for my $fourth (@group4) {
                # Assume fixed size = 2
                # $first, $second and $third repeat here for each member in @group4
                # $first, $second pairings happen multiple times
            }
        }
    }
} 

##</code><code>##

A sample to work with:

group_1 = A B C
group_2 = 1 2 3 4
group_3 = yellow blue green
group_4 = tiny small medium large gigantic

fixed_size = 2