<?php
header('content-type:text/html;charset=utf-8');
# if(isset($_post['提交'])){
$username = $_post['username'];
$password = $_post['password'];
if(empty($username)||empty($password)){
header('Refresh:3;url=login.php');
echo '使用者名稱密碼不能為空';
exit;
}
}else{
## clude_once 'templates/login.html'; } ?>
找出問題了，是php的變數沒注意區分大小寫