$re = '/pps=\[?([^;]+)/';
$str = 'http://www.abcexample.com/landpage/?pps=[Y/lyPw==;id_1][Y/lyP2ZZYxi==;id_2];[5403;ord];
http://www.abcexample.com/landpage/?pps=Y/lyPw==;id_1;unknown;ord;
';
preg_match_all($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