求截取PHP指定字符串代码,该怎么解决

$s = 'aaaa
bbbb
cccc
dddd
';
echo preg_replace('/
\w+/', '', $s, 2);

aaaa
dddd

echo preg_replace('/
[^<]+/', '', $s, 2);

echo preg_replace('/\(.+?\)/', '', $s);

echo preg_replace_callback('/
[^<]+/', 'foo', $s, 2); 
function foo($m){
     return strpos($m[0], '(') !== false ? preg_replace('/\(.+?\)/','',$m[0]) : '';	    	 
}