$filename ="bbbbbbb";
$dir = dirname(__FILE__);
$path = $dir."".DIRECTORY_SEPARATOR."config.php";
echo $path;
$contents = file_get_contents($path);
$contents = modify_ini_value($contents,"theme",$filename);
file_put_contents($path,$contents);

function modify_ini_value($content,$key,$replace){
	$match = '/([ \t]*)(\$'.$key.'\s*=\s*\"?)(.*?)(\"?)(\s*;\s*$)/m';
	return (preg_replace($match,"\${1}\${2}{$replace}\${4}\${5}",$content));
}

?