$re = '/{{([^},]+)(?:,([^}]+))?}}/';
$str = 'This is my first example string. {{foo}} This is what it looks like.
This is my second example string. {{1,2}}. This is what it looks like.
This is my third example string. {{a,b}} and {{2}}. This is';
preg_match_all($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