$re = '/ref="[^"\r\n]*"/m';
$str = '[show_portfolio get="yachts" for="sale" in="europe" sort="length_overall" by="asc" page="1" perpage="18" theme="active-71" ref="http://replaceme.com" debug="true" engine="engine.com"]
[get_portfolio get="yachts" for="sale" in="europe" sort="length_overall" by="asc" page="1" perpage="18" theme="active-71" ref="http://replaceme.com" debug="true" engine="engine.com"]';
preg_match_all($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