幾乎任何使用 TCP，UDP或UNIX-domain socket的動作都可以用nc來達成，常見的功能如。
- simple TCP proxies
- shell-script based HTTP clients and servers
- network daemon testing
- a SOCKS or HTTP ProxyCommand for ssh(1)
- and much, much more
SYNOPSIS
nc [-46bCDdhklnrStUuvZz] [-I length] [-i interval] [-O length]
[-P proxy_username] [-p source_port]
[-q seconds] [-s source] [-T toskeyword] [-V rtable]
[-w timeout] [-X proxy_protocol] [-x proxy_address[:port]]
[destination] [port]
options: -v, verbose
不加-v，發生錯誤時不會有訊息。brook@vista:~$ nc 127.0.0.1 12345 brook@vista:~$ nc -v 127.0.0.1 12345 nc: connect to 127.0.0.1 port 12345 (tcp) failed: Connection refused brook@vista:~$ nc -v 127.0.0.1 80 Connection to 127.0.0.1 80 port [tcp/http] succeeded! 輸入GET / HTTP/1.1 輸入HOST: 127.0.0.1 輸入[enter] 輸入[enter] HTTP/1.1 200 OK Date: Tue, 27 Jan 2015 08:24:17 GMT Server: Apache/2.2.22 (Ubuntu) Last-Modified: Mon, 23 Dec 2013 04:13:45 GMT ETag: "1b806ff-b1-4ee2bdaa24ac8" Accept-Ranges: bytes Content-Length: 177 Vary: Accept-Encoding Content-Type: text/html X-Pad: avoid browser bug <html><body><h1>It works!</h1> <p>This is the default web page for this server.</p> <p>The web server software is running but no content has been added, yet.</p> </body></html>
options: -l, listen for an incoming connection rather than initiate a connection to a remote host
等同開socket在listen，預設是tcp。brook@vista:~$ nc -l 127.0.0.1 5000 -> server brook@vista:~$ netstat -nal | grep 5000 tcp 0 0 127.0.0.1:5000 0.0.0.0:* LISTEN brook@vista:~$ nc 127.0.0.1 5000 -> client
options: -u, Use UDP instead of the default option of TCP.
使用UDP取代預設的TCPbrook@vista:~$ nc -lu 127.0.0.1 5000 -> server brook@vista:~$ nc -u 127.0.0.1 5000 -> client
使用nc當Web Server
{ echo -ne "HTTP/1.0 200 OK\r\nContent-Length: $(wc -c < some.file)\r\n\r\n"; cat some.file; } | nc -l 5050
開啟Browser，http://127.0.0.1:5050/，就可以看到網頁了。
Works as a Port Scanner
brook@vista:~$ nc -v -z 127.0.0.1 80-200 2>&1 | grep -v failed Connection to 127.0.0.1 80 port [tcp/http] succeeded! Connection to 127.0.0.1 139 port [tcp/netbios-ssn] succeeded!
Transfering Files
sender brook@vista:~$ md5sum usb_eth.txt 2367562f85f99fe972b9d6a83ce38099 usb_eth.txt brook@vista:~$ tar cvf - usb_eth.txt | nc 127.0.0.1 5000 usb_eth.txt receiver brook@vista:/tmp$ nc -l 5000 | tar xvf - usb_eth.txt brook@vista:/tmp$ md5sum usb_eth.txt 2367562f85f99fe972b9d6a83ce38099 usb_eth.txt
Git Proxy
以下的Script是我拿用當gitproxy用的
#!/bin/bash
# http://tech-tacolin.blogspot.tw/2013/04/git-http-proxy.html
PROXY=1.2.3.4
PROXYPORT=3128
case $1 in
192.168.1.1 | internal-ip)
nc -X connect $*
;;
*)
nc -x $PROXY:$PROXYPORT -X connect $*
;;
esac
