Randomly generate four yards of English

 //產生隨機碼，預設四碼，約七百次會出現碰撞
function get_random_key($length = 4)
{
$permitted_chars = '1234567890abcdefghijklmnopqrstuvwxyxABCDEFGHIJKLMNOPQRSTUVWXYX';
return substr(str_shuffle($permitted_chars), 0, $length);
}