$re = '`^%(\w{3})\s+(\d+)\s*([0-9]+\s?:\s?[0-9]+\s?:\s?[0-9]+):[0-9]+\s*(\d{4})?\s*\S*\s*(.*)/(\d+)/\S*:(?:(.*);)?(.*)`';
$str = '%May 11 10:03:51:122 2000 AB-CD-E SSH/6/SSH_LOGOUT: STEL user manager (IP: 172.0.0.0) logged out.
';
preg_match_all($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