#!/usr/bin/perl

use strict;
use warnings;

my @alphabet = ((1..9) , qw(a b c));

sub enum_words {
    my ($word, $maxlength) = @_;
    if (length $word < $maxlength) {
        for my $char (@alphabet) {
            enum_words($word . $char, $maxlength);
        }
    }
    else {
        print "$word\n";
    }
}

for my $length (1 .. 4) {
    enum_words('', $length);
}