gistfile1.pl

sub permutation {
	my ( $count, $columns, $permutations ) = @_;
	my $total_permutations = @$permutations ** $columns;

	return if $count >= $total_permutations;

	my $num = $count;
	my $base = @$permutations;

	my $s = '';

    while (1) {
    	my $r = $num % $base;
    	$s = $permutations->[$r] . $s;
    	$num = int($num / $base);
    	last if $num == 0;
    }

    while ( length( $s ) < $columns ) {
    	$s = $permutations->[0] . $s;
    }

    return $s;
}

my $i=0;
while (1) {
	my $p = permutation( $i++, 3, [qw( 0 3 6 9 C F )] );
	if ( defined $p ) {
		print "$p\n";
	} else {
		last;
	}
}