Select Code to Download

my $rx = qr/
    ([abcd])           # a, b, c, or d -- stored in \1
...
    (?!\1|\2|\3)       # next thing not \1, \2, or \3
    [abcd]             # you get the idea
    /x;

use List::Util qw( shuffle );
use Test::More;
...
    my $s = join q{}, shuffle 0 .. 9, qw( a b c d );
    ok( $s =~ $rx, "match '$s'" );
}