Of course, that still leaves 'badw0rd' and 'b_a_d_w_o_r_d', but it is a start. I would be more restrictive:

(my $test = $input) =~ s/[^A-Z]//ig;
[download]

This will still permit 'baaadwooord', unfortunately.

I'm inclined to agree with [id://phaylon], in that there is no substitute for moderation. :)

Update: forgot the ^ character. <blush>