$re = '/W\s+\K\S+/m';
$str = ' X12 IK 888T
G I5J P9
544T ZUK ONI
E6U5 Z339988 T8 N55
886 W 9ZT T95';
preg_match_all($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