Match specific length x or y

Question

I\'d like a regex that is either X or Y characters long. For example, match a string that is either 8 or 11 characters long. I have currently implemented this like

Answer 1

With Perl, you could do:

my $re = qr/here_is_your_regex_part/;
my $full_regex = qr/$re{8}(?:$re{3})?$/