$re = '/<a[^>]+href=("|\')([^"\'?]*)[^"\']*\1[^>]*>/i';
$str = '<a href="/go/page/mobile_download_apps.html?&who=r,6GDewh28SCW3/fUSqmWqR_E9ljkcH1DheIMqgbiHjlX3OBDbskcuCZ22iDvk0zeZR7BEthcEaXGFWaQ4Burmd4eKuhMpqojjDE6BrCiUtLClkT32CejpMIdnqVOUmWBD">';
preg_match_all($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