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

use Algorithm::Combinatorics qw(variations_with_repetition);

my @data = ('', 'a'..'z', 'A'..'Z','_');
my $iter = variations_with_repetition(\@data, 6);

while (my $p = $iter->next) {
    my $plain = join '', values $p;
    print $plain,'.';
}