$re = '/OnUploadCompleted\([0-9]+\s*,\s*\"\/(.+?)\"/m';
$str = '<script type="text/javascript">
(function(){var d=document.domain;while (true){try{var A=window.parent.document.domain;break;}catch(e)
{};d=d.replace(/.*?(?:\\.|$)/,\'\');if (d.length==0) break;try{document.domain=d;}catch (e){break;}}})();
window.parent.OnUploadCompleted(0,"/userfiles/abc.txt","abc.txt", "") ;</script>';
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