$re = '/(\s)([0-9]{4,})(\s?)/m';
$str = 'Terrace 07541207031 RDL 18.02
Terrace 07541 RDL 18.02
Terrace 075adf8989 RDL 18.02
Terrace 075adf898 RDL 18.02
075898 RDL 18.02
Terrace RDL 98989';
preg_match_all($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