要求
1：只看http返回的头信息
2：发送get请求
[ly@lypc ~]$ curl -I -X GET http://www.qq.com
HTTP/1.1 200 OK
Server: squid/3.4.1
Date: Mon, 05 Jan 2015 03:32:34 GMT
Content-Type: text/html; charset=GB2312
Transfer-Encoding: chunked
Connection: keep-alive
Vary: Accept-Encoding
Expires: Mon, 05 Jan 2015 03:33:34 GMT
Cache-Control: max-age=60
Vary: Accept-Encoding
X-Cache: HIT from shanghai.qq.com
注意：以上curl版本为：
curl 7.29.0