$re = '/[a-zA-Z]{2}[0-9]{2}[\s*]{0,}[0-9]{4}[\s*]{0,}[0-9]{4}[\s*]{0,}[0-9]{4}[\s*]{0,}[0-9]{4}[\s*]{0,}[0-9]{4}[\s*]{0,}/';
$str = 'ES12 3456 7890 1234 5678 9012';
preg_match($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