use strict;
use warnings;

my @chartab = (0..9, 'a'..'z');
my $depth = 4;
print permute(\@chartab,'',$depth);

sub permute {
    my ($chartab_ref, $intro, $depth) = @_;
    return "$intro," if ($depth == 0);

    my $string = q{};
    foreach my $letter (@$chartab_ref) {
        $string .= permute($chartab_ref, $intro.$letter,$depth-1);
    }
    return $string;
}