最近在研究如何测试代理服务器的速度以便选出最快的服务器，找了一圈发现其实系统自带的curl命令就能实现这个功能。
curl命令的各个参数的介绍网上有很多，这里只给出几个常用的：
curl 不输出任何信息,安静模式,走代理：
curl -x socks5://127.0.0.1:1086 -m 10 -s -o /dev/null www.baidu.com
-m 整个访问的超时时间
-s 安静模式，不输出连接速度等信息
-o path 输出output到path
其中/dev/null是个特殊路径：
/dev/null null是一个名叫null小桶的东西，如果命令的输出不想要即想丢弃输出的内容，既不想在标准输出与不想重定向到某个文件，就可将命令的输出重定向到/dev/null。这样做的好处是不会因为输出的内容过多而导致文件大小不断的增加。
-x 走代理：
-x, --proxy [protocol://]host[:port] Use this proxy
--proxy-anyauth Pick any proxy authentication method
--proxy-basic Use Basic authentication on the proxy
--proxy-cacert <file> CA certificate to verify peer against for proxy
--proxy-capath <dir> CA directory to verify peer against for proxy
--proxy-cert <cert[:passwd]> Set client certificate for proxy
--proxy-cert-type <type> Client certificate type for HTTPS proxy
--proxy-ciphers <list> SSL ciphers to use for proxy
--proxy-crlfile <file> Set a CRL list for proxy
--proxy-digest Use Digest authentication on the proxy
--proxy-header <header/@file> Pass custom header(s) to proxy
--proxy-insecure Do HTTPS proxy connections without verifying the proxy
--proxy-key <key> Private key for HTTPS proxy
--proxy-key-type <type> Private key file type for proxy
--proxy-negotiate Use HTTP Negotiate (SPNEGO) authentication on the proxy
--proxy-ntlm Use NTLM authentication on the proxy
--proxy-pass <phrase> Pass phrase for the private key for HTTPS proxy
--proxy-pinnedpubkey <hashes> FILE/HASHES public key to verify proxy with
--proxy-service-name <name> SPNEGO proxy service name
--proxy-ssl-allow-beast Allow security flaw for interop for HTTPS proxy
--proxy-tls13-ciphers <ciphersuite list> TLS 1.3 proxy cipher suites
--proxy-tlsauthtype <type> TLS authentication type for HTTPS proxy
--proxy-tlspassword <string> TLS password for HTTPS proxy
--proxy-tlsuser <name> TLS username for HTTPS proxy
--proxy-tlsv1 Use TLSv1 for HTTPS proxy
知道了这些，就成功了一半。
为了统计延时，需要用到curl命令中自带的一些宏定义。
time_namelookup：DNS 解析域名的时间
time_commect：client和server端建立TCP 连接的时间
time_starttransfer：从client发出请求；到web的server 响应第一个字节的时间
time_total：client发出请求；到web的server发送会所有的相应数据的时间
speed_download：下周速度 单位 byte/s
我们来完善一下上面的命令：
➜ ~ curl -o /dev/null -x socks5://127.0.0.1:1086 -s -w %{time_namelookup}---%{time_connect}---%{time_starttransfer}---%{time_total}---%{speed_download}"\n" www.baidu.com
0.000072---0.020414---0.587005---0.587225---4056.000
上面这条命令及返回结果可以这么理解：
0.000072: DNS 服务器解析域名的时间单位是0.000072s
0.020414: client发出请求，到c/s 建立TCP 的时间；里面包括DNS解析的时间
0.587005: client发出请求；到s响应发出第一个字节开始的时间；包括前面的2个时间
0.587225: client发出请求；到s把响应的数据全部发送给client；并关闭connect的时间
4056.000 ：下载数据的速度
建立TCP连接到server返回client第一个字节的时间：0.587005s – 0.020414s = 0.566591s
server把响应数据发送给client的时间：0.587225s – 0.587005s = 0.00022s
当然，还有很多：
url_effective
filename_effective The ultimate filename that curl writes out to. This is only meaningful 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. (Added in 7.25.1)
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client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.)
size_download 下载大小。(The total amount of bytes that were downloaded.)
size_upload 上传大小。(The total amount of bytes that were uploaded.)
size_header 下载的header的大小(The total amount of bytes of the downloaded headers.)
size_request 请求的大小。(The total amount of bytes that were sent in the HTTP request.)
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.)
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.)
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.)
num_connects Number of new connects made in the recent transfer. (Added in 7.12.3)
num_redirects Number of redirects that were followed in the request. (Added in 7.12.3)
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)
ftp_entry_path The initial path libcurl ended up in when logging on to the remote FTP server. (Added in 7.15.4)
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))
当然，如果你觉得这么显示不容易看的话，还可以指定格式化文件：
创建如下文本文件：
➜ vim curl-time
\n
http: %{http_code}\n
dns: %{time_namelookup}s\n
redirect: %{time_redirect}s\n
time_connect: %{time_connect}s\n
time_appconnect: %{time_appconnect}s\n
time_pretransfer: %{time_pretransfer}s\n
time_starttransfer: %{time_starttransfer}s\n
size_download: %{size_download}bytes\n
speed_download: %{speed_download}B/s\n
----------\n
time_total: %{time_total}s\n
\n
然后利用-w参数指定格式化文件，最终效果:
➜ curl -o /dev/null -x socks5://127.0.0.1:1086 -s -w "@curl-time" www.google.com
http: 200
dns: 0.000070s
redirect: 0.000000s
time_connect: 0.018721s
time_appconnect: 0.000000s
time_pretransfer: 0.018743s
time_starttransfer: 0.274720s
size_download: 13065bytes
speed_download: 47509.000B/s
----------
time_total: 0.275102s