$re = '/(?<=X)[0-9\.]+(?= )/';
$str = 'N9 G00 X2675.766 Y427.409 Z730
N11 G00 X2675.766 Y427.409
N13 G00 X2675.766 Y427.409
N15 G00 X2675.766 Y427.409 Z505
N17 F4000';
preg_match_all($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