$re = '/CN=(?P<first>[^,]+),\s*
(?P<last>[^,]+)/x';
$str = 'CN=First\\, Last,OU=Standard users,OU=Users,OU=Place,OU=DOMAIN,DC=dfe,DC=stuff,DC=asdf';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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