#! perl
use strict;
use warnings;

my $re = qr{ ( \d{4} ) \. htm l? $ }ix;

/$re/ && print "$1\n" while <DATA>;

__DATA__
http://test-text-ad-1234.html
http://test-abc0000.htmdef-ad-5678.HTM
test-ghijk-ad-XXXX.html

##</code><code>##

12:39 >perl 1616_SoPW.pl
1234
5678

12:39 >