$re = '/(?ms)Message\=\"(?<Message>.+)\s+SID/m';
$str = 'Message="Internal event: Function ldap_search entered.
SID: S-1-5-18
Source IP: 127.0.0.1:25855
Operation identifier: 680571
Data1:
Data2: 2796807187
Data3:
Data4:"';
preg_match_all($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