$re = '/^.+(\.[^.]+)$(?=\s*(?:(?!<tag>)[^.])+\1)|^(?!<tag>)[^.]+/m';
$str = '<tag>Adventures of Shuggy</tag>
!Shuggy.png
!Sound Bank.txt
test.txt
4.lwav
5.lwav
6.lwav
88.lwav
89.lwav
<tag>Adventures of Jack</tag>
90.lwav
91.lwav
92.lwav
93.lwav
!Sound Bank.xsb';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php