使用curl命令怎么返回状态码

参考：
https://www.cnblogs.com/chuanzhang053/p/16355454.html
使用curl命令返回页面内容，在一些检测网页的需求中只需要返回页面状态码来判断页面是否正常
使用以下命令判断百度是否正常，返回状态码为200则代表正常

# curl -o  /dev/null -s -w "%{http_code}\n" https://www.baidu.com
# 200

参数解释

# 把输出重定向为空
# -o /dev/null
# 安静输出，只返回显示结果
# -s
# 输出想要显示的内容，本次输出状态码，正常为200
# -w "%{http_code}\n"

-w参数其他内容

1. url_effective 最终获取的url地址，尤其是当你指定给curl的地址存在301跳转，且通过-L继续追踪的情形。
2. http_code http状态码，如200成功,301转向,404未找到,500服务器错误等。(The numerical response code that was found in the last retrieved HTTP(S) or FTP(s) transfer. In 7.18.2 the alias response_code was added to show the same info.)
3. http_connect The numerical code that was found in the last response (from a proxy) to a curl CONNECT request. (Added in 7.12.4)
4. time_total 总时间，按秒计。精确到小数点后三位。 （The total time, in seconds, that the full operation lasted. The time will be displayed with millisecond resolution.）
5. time_namelookup DNS解析时间,从请求开始到DNS解析完毕所用时间。(The time, in seconds, it took from the start until the name resolving was completed.)
6. time_connect 连接时间,从开始到建立TCP连接完成所用时间,包括前边DNS解析时间，如果需要单纯的得到连接时间，用这个time_connect时间减去前边time_namelookup时间。以下同理，不再赘述。(The time, in seconds, it took from the start until the TCP connect to the remote host (or proxy) was completed.)
7. time_appconnect 连接建立完成时间，如SSL/SSH等建立连接或者完成三次握手时间。(The time, in seconds, it took from the start until the SSL/SSH/etc connect/handshake to the remote host was completed. (Added in 7.19.0))
8. time_pretransfer 从开始到准备传输的时间。(The time, in seconds, it took from the start until the file transfer was just about to begin. This includes all pre-transfer commands and negotiations that are specific to the particular protocol(s) involved.)
9. time_redirect 重定向时间，包括到最后一次传输前的几次重定向的DNS解析，连接，预传输，传输时间。(The time, in seconds, it took for all redirection steps include name lookup, connect, pretransfer and transfer before the final transaction was started. time_redirect shows the complete execution time for multiple redirections. (Added in 7.12.3))
10. time_starttransfer 开始传输时间。在发出请求之后，Web 服务器返回数据的第一个字节所用的时间(The time, in seconds, it took from the start until the first byte was just about to be transferred. This includes time_pretransfer and also the time the server needed to calculate the result.)
11. size_download 下载大小。(The total amount of bytes that were downloaded.)
12. size_upload 上传大小。(The total amount of bytes that were uploaded.)
13. size_header 下载的header的大小(The total amount of bytes of the downloaded headers.)
14. size_request 请求的大小。(The total amount of bytes that were sent in the HTTP request.)
15. speed_download 下载速度，单位-字节每秒。(The average download speed that curl measured for the complete download. Bytes per second.)
16. speed_upload 上传速度,单位-字节每秒。(The average upload speed that curl measured for the complete upload. Bytes per second.)
17. content_type 就是content-Type，不用多说了，这是一个访问我博客首页返回的结果示例(text/html; charset=UTF-8)；(The Content-Type of the requested document, if there was any.)
18. num_connects 最近的的一次传输中创建的连接数目。Number of new connects made in the recent transfer. (Added in 7.12.3)
19. num_redirects 在请求中跳转的次数。Number of redirects that were followed in the request. (Added in 7.12.3)
20. redirect_url When a HTTP request was made without -L to follow redirects, this variable will show the actual URL a redirect would take you to. (Added in 7.18.2)
21. ftp_entry_path 当连接到远程的ftp服务器时的初始路径。The initial path libcurl ended up in when logging on to the remote FTP server. (Added in 7.15.4)
22. ssl_verify_result ssl认证结果，返回0表示认证成功。( The result of the SSL peer certificate verification that was requested. 0 means the verification was successful. (Added in 7.19.0))