如何使用任何网址（www.w3schools.com）获取php中的请求标头

how to get request headers in php using any url give the details like this(Pragma,Accept-Charset,Accept-Encoding,Host,Accept-Language,User-Agent,Accept,Cache-Control,Connection) give the value.

Try

<?php 
echo "<pre>";
print_r($_SERVER);
    ?>