在需要引用header的页面：

 <?php
$page_title = 'default page name';
$page_css = '';
$page_script = '';
require_once('header.php');
?>

header.php:

 <header>
    <title><?=$page_title?></title>

    <link rel="stylesheet" href="global.css">
    <?=$page_css?>

    <script src="jquery.js"></script>
    <?=$page_script?>
</header>