$re = '/^([^-\n]*-[^=\n]*)-.*?(\.\w+)$/m';
$str = 'Tab 3-3-z-o.pdf
Should be Tab 3-3.pdf
Tab 2-3-jk2.pdf
Should be: Tab 2-3.pdf
Tab 3-3-Yuwk-3-k-l-s.pdf
Should be: Tab 3-3.pdf';
preg_match_all($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