太长不看版
curl -s -w "%{time_total}\n" -o /dev/null http://www.github.com/
0.106368
可以看到返回是0.106368秒。解释一下这几个参数：
-s, --silent： 让 curl 保持静默模式，不会输出进度条-w "%{time_total\n}"：输出请求的总时间-o /dev/null： 这个参数用来隐藏 response 的内容
原理
这里是curl关于-w参数的文档；输出curl请求的具体时间，其实是用到了-w参数；这个参数提供了很多请求中的信息，作为变量用于格式化输出（详见下面的可用的--write-out变量表格）。
使用方式
这里是使用它的三种方式：
- 通过纯文本传递
curl -w "formatted string" http://example.com/ - 通过文件读取
curl -w "formatted string" http://example.com/ - 通过
stdin读取（跟读取文件类似，不过-在这里代表stdin）curl -w @- http://example.com/
在由你自己定义的输出格式中，可以使用%{variable_name}的方式来访问可用的变量；如果要输出%字符，需要转义成%%；您还可以使用 、回车符和制表符空格来输出换行符。
回看上面的例子：
curl -w "%{time_total}\n" http://www.github.com/
这里就是简单地输出了一个time_total的变量值。
如果要输出HTTP Response Header
在字符串中使用%header{name} ，其中 name 是不区分大小写的标头名称（不带尾随冒号）。
curl -w "Server: %header{server}\n" http://example.com
cURL -w支持的所有变量
某些变量在老的curl版本中不可用，请注意。
| Variable | Description 描述 |
|---|---|
certs | Outputs the certificate chain from the most recent TLS handshake - with details. (Introduced in 7.88.0)输出最近 TLS 握手的证书链 - 包含详细信息。 （7.88.0中引入） |
content_type | Content-Type of the requested document, if there was any.所请求文档的内容类型（如果有）。 |
errormsg | Error message from the transfer. Empty if no error occurred. (Introduced in 7.75.0)来自传输的错误消息。如果没有发生错误则为空。 （7.75.0 中引入） |
exitcode | Numerical exit code from the transfer. 0 if no error occurred. (Introduced in 7.75.0)传输的数字退出代码。如果没有发生错误则为 0。 （7.75.0 中引入） |
filename_effective | The ultimate filename that curl writes out to. Practical if curl is told to write to a file with the --remote-name or --output option. It’s most useful in combination with the --remote-header-name option.curl 写入的最终文件名。如果告诉curl 使用 --remote-name 或 --output 选项写入文件，则实用。它与 --remote-header-name 选项结合使用时最有用。 |
ftp_entry_path | The initial path curl ended up in when logging on to the remote FTP server.登录远程 FTP 服务器时，curl 的初始路径结束。 |
http_code | The former variable name for what is now known as response_code.以前的变量名称现在称为 response_code 。 |
http_connect | the numerical code that was found in the last response (from a proxy) to a curl CONNECT request.在对curl CONNECT 请求的最后响应（来自代理）中找到的数字代码。 |
http_version | The HTTP version that was used.使用的 HTTP 版本。 |
json | all write-out variables as a single JSON object. (Introduced in 7.72.0)所有写出变量作为单个 JSON 对象。 （7.72.0中引入） |
local_ip | IP address of the local end of the most recently used connection - can be either IPv4 or IPv6最近使用的连接的本地端的 IP 地址 - 可以是 IPv4 或 IPv6 |
local_port | Local port number of the most recently used connection最近使用的连接的本地端口号 |
method | HTTP method the most recent request used最近请求使用的 HTTP 方法 |
num_certs | Number of the certificates in the most recent TLS handshake. (Introduced in 7.88.0)最近 TLS 握手中的证书数量。 （7.88.0中引入） |
num_connects | Number of new connects made in the recent transfer.最近传输中建立的新连接数。 |
num_headers | Number of response headers in the last response上次响应中响应头的数量 |
num_redirects | Number of redirects that were followed in the request.请求中遵循的重定向数。 |
onerror | If the transfer ended with an error, show the rest of the string, otherwise stop here. (Introduced in 7.75.0)如果传输因错误而结束，则显示字符串的其余部分，否则在此停止。 （7.75.0 中引入） |
proxy_ssl_verify_result | The result of the SSL peer certificate verification that was requested when communicating with a proxy. 0 means the verification was successful.与代理通信时请求的 SSL 对等证书验证的结果。 0表示验证成功。 |
redirect_url | The actual URL a redirect would take you to when an HTTP request was made without -L to follow redirects.当发出 HTTP 请求而没有 -L 遵循重定向时，重定向将带您到达的实际 URL。 |
remote_ip | The remote IP address of the most recently used connection — can be either IPv4 or IPv6.最近使用的连接的远程 IP 地址 — 可以是 IPv4 或 IPv6。 |
remote_port | The remote port number of the most recently made connection.最近建立的连接的远程端口号。 |
response_code | The numerical response code that was found in the last transfer.在上次传输中找到的数字响应代码。 |
scheme | scheme used in the previous URL上一个 URL 中使用的方案 |
size_download | Total number of bytes that were downloaded.下载的总字节数。 |
size_header | Total number of bytes of the downloaded headers.下载标头的总字节数。 |
size_request | Total number of bytes that were sent in the HTTP request.HTTP 请求中发送的字节总数。 |
size_upload | Total number of bytes that were uploaded.上传的总字节数。 |
speed_download | Average download speed that curl measured for the complete download in bytes per second.curl 测量的完整下载的平均下载速度（以字节/秒为单位）。 |
speed_upload | Average upload speed that curl measured for the complete upload in bytes per second.curl 测量的完整上传的平均上传速度（以字节/秒为单位）。 |
ssl_verify_result | the result of the SSL peer certificate verification that was requested. 0 means the verification was successful.所请求的 SSL 对等证书验证的结果。 0表示验证成功。 |
stderr | Makes the rest of the output get written to stderr.使输出的其余部分写入 stderr。 |
stdout | makes the rest of the output get written to stdout.使输出的其余部分写入标准输出。 |
time_appconnect | The time in seconds, it took from the start until the SSL/SSH/etc connect/handshake to the remote host was completed.从开始到完成与远程主机的 SSL/SSH/etc 连接/握手所花费的时间（以秒为单位）。 |
time_connect | The time in seconds, it took from the start until the TCP connect to the remote host (or proxy) was completed.从开始到完成与远程主机（或代理）的 TCP 连接所花费的时间（以秒为单位）。 |
time_namelookup | The time in seconds, it took from the start until the name resolving was completed.从开始到名称解析完成所花费的时间（以秒为单位）。 |
time_pretransfer | 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.从开始到文件传输即将开始所花费的时间（以秒为单位）。这包括特定于所涉及的特定协议的所有预传输命令和协商。 |
time_redirect | The time in seconds, it took for all redirection steps including name lookup, connect, pre-transfer and transfer before the final transaction was started. time_redirect the complete execution time for multiple redirections.以秒为单位的时间，在最终事务开始之前，所有重定向步骤（包括名称查找、连接、预传输和传输）所花费的时间。 time_redirect 多次重定向的完整执行时间。 |
time_starttransfer | 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.从开始到第一个字节即将传输所花费的时间（以秒为单位）。这包括 time_pretransfer 以及服务器计算结果所需的时间。 |
time_total | The total time in seconds, that the full operation lasted. The time will be displayed with millisecond resolution.完整操作持续的总时间（以秒为单位）。时间将以毫秒分辨率显示。 |
url | The URL used in the transfer. (Introduced in 7.75.0)传输中使用的 URL。 （7.75.0 中引入） |
url_effective | The URL that was fetched last. This is particularly meaningful if you have told curl to follow Location: headers (with -L).最后获取的 URL。如果您告诉curl 遵循 Location: 标头（使用 -L ），这尤其有意义。 |
urlnum | 0-based numerical index of the URL used in the transfer. (Introduced in 7.75.0)传输中使用的 URL 从 0 开始的数字索引。 （7.75.0 中引入） |
进阶版
这个版本是为了一次性输出所有的时间格式；
将下面的内容写入到curl-fmt.txt文件中：
\n
time_namelookup: %{time_namelookup}\n
time_connect: %{time_connect}\n
time_appconnect: %{time_appconnect}\n
time_pretransfer: %{time_pretransfer}\n
time_redirect: %{time_redirect}\n
time_starttransfer: %{time_starttransfer}\n
----------\n
time_total: %{time_total}\n
在curl-fmt.txt的目录下执行：
curl -s -w "@curl-fmt.txt" -o /dev/null http://www.baidu.com/
curl输出结果：
time_namelookup: 0.012421
time_connect: 0.024995
time_appconnect: 0.000000
time_pretransfer: 0.025187
time_redirect: 0.000000
time_starttransfer: 0.041807
----------
time_total: 0.041905