$re = '/^([ ])?\[(\/?)gaiarch(=[^"]*)?]([ ])?|([ ])?\[(\/?)gaiarch(=[^"]*)?]([ ])?$/i';
$str = '[gaiarch=slider]
[img url="http://i1251.photobucket.com/albums/hh543/Knight-Yoshi/trade_c.png" text="Trading Image" goto="http://www.gaiaonline.com/gaia/bank.php?mode=trade&uid=15388423"],[img url="http://i1251.photobucket.com/albums/hh543/Knight-Yoshi/friend_c.png" text="Friends Image" goto="http://www.gaiaonline.com/friends/add/15388423"][/gaiarch]
[gaiarch=slider][img url="http://i1251.photobucket.com/albums/hh543/Knight-Yoshi/gaiaonline/thread/post/dark-center_bottom_zps419960f4.gif" text="bottom bar"]
[img url="http://i1251.photobucket.com/albums/hh543/Knight-Yoshi/gaiaonline/thread/post/star-say_right_zpsdc3769f3.png" goto="http://www.gaiaonline.com/"][/gaiarch] ';
preg_match_all($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