### curl 参数

curl 命令提供了 -w 参数，这个参数在 manpage 是这样解释的：

-w, --write-out <format>
Make curl display information on stdout after a completed transfer. The format is a string that may contain plain text mixed with any number of variables. The  format
can  be  specified  as  a literal "string", or you can have curl read the format from a file with "@filename" and to tell curl to read the format from stdin you write
"@-".

The variables present in the output format will be substituted by the value or text that curl thinks fit, as described below. All variables are specified  as  %{vari‐
able_name} and to output a normal % you just write them as %%. You can output a newline by using \n, a carriage return with \r and a tab space with \t.

$curl -o /dev/null -s -w "time_connect: %{time_connect}\ntime_starttransfer: %{time_starttransfer}\ntime_nslookup:%{time_namelookup}\ntime_total: %{time_total}\n" "https://www.baidu.com" time_connect: 0.009 time_starttransfer: 0.065 time_nslookup:0.007 time_total: 0.065 ### 步骤 先往文本文件 curl.txt 写入下面的内容：  time_namelookup: %{time_namelookup}\n time_connect: %{time_connect}\n time_appconnect: %{time_appconnect}\n time_redirect: %{time_redirect}\n time_pretransfer: %{time_pretransfer}\n time_starttransfer: %{time_starttransfer}\n ----------\n time_total: %{time_total}\n 每个变量的解释如下： time_namelookup：DNS 域名解析的时候，就是把 https://baidu.com 转换成 ip 地址的过程 time_connect：TCP 连接建立的时间，就是三次握手的时间 time_appconnect：SSL/SSH 等上层协议建立连接的时间，比如 connect/handshake 的时间 time_redirect：从开始到最后一个请求事务的时间 time_pretransfer：从请求开始到响应开始传输的时间 time_starttransfer：从请求开始到第一个字节将要传输的时间 time_total：这次请求花费的全部时间 ### 示例 例子： $ curl -w "@curl.txt" -o /dev/null -s -L  'http://www.baidu.com'
time_namelookup:  0.004
time_connect:  0.015
time_appconnect:  0.000
time_redirect:  0.000
time_pretransfer:  0.015
time_starttransfer:  0.027
----------
time_total:  0.027

-w：从文件中读取要打印信息的格式
-o /dev/null：把响应的内容丢弃，因为我们这里并不关心它，只关心请求的耗时情况
-s：不要打印进度条

DNS 查询：4ms
TCP 连接时间：pretransfter(15) - namelookup(4) = 11ms

### -w 参数详解

• 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。
• 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.)
• 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)
• 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.）
• 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.)
• 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.)
• 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))
• 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.)
• 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))
• 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.)