$re = '/(2[0-9]+)/m';
$str = '2019 RTM-CU8
2017 RTM-CU10
2016 SP2-CU14
2017 RTM-CU31
2019 RTM-CU14
2016 SP2-CU7
';
preg_match_all($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