$re = '/\.GPS\.\s+\K\d+/s';
$str = 'Wed Aug 27 20:24:53.536 IST
address ref clock st when poll reach delay offset disp
*~172.16.18.163 .GPS. 1 657 1024 377 13.99 1.801 19.630
~127.127.1.1 .LOCL. 3 15 64 377 0.00 0.000 1.920
* sys_peer, # selected, + candidate, - outlayer, x falseticker, ~ configured';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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