$re = '/\s*(\d{1,5})?\s*(?:<(?<pri>\d{1,3})>)/im';
$str = '23123<123>
123 <1>
123 <123>
123<12>
<123>
<1>';
preg_match_all($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