$re = '/\[\[(.*)\]\]/mU';
$str = 'Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed aliquet imperdiet sapien, [[xx]] vitae luctus augue convallis quis. Pellentesque felis eros, dignissim vitae [[ccvf] dignissim sed, porta a leo. Duis tincidunt, ex sit amet sollicitudin vehicula, nibh velit ultrices ipsum, at feugiat enim arcu et [[dfg]] enim. [[abc Lorem ipsum [[xyz]] dolor sit amet, consectetur adipiscing elit. Sed aliquet imperdiet sapien.';
preg_match_all($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