$re = '/(.*)pl_\w\w(.*)(\?Id=\d+)?&?.*/m';
$str = '1. http://www.example.com/myplan/mp/public/pl_be?Id=543543×tamp=06280435435
2. http://www.example.com/course/df/public/pl_de?Id=454354×tamp=0628031746
3. http://www.example.com/book/rg/public/pl_fo?Id=4445577×tamp=0628031734
4. http://www.example.com/trip/tr/public/pl_ds?Id=454354×tamp=06280314546
5. http://www.example.com/trip/tr/public/pl_ds';
preg_match_all($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