[/home/jackxiang/netcat]# rpm -ihv netcat-0.7.1-1.i386.rpm
warning: netcat-0.7.1-1.i386.rpm: Header V3 DSA signature: NOKEY, key ID b2d79fc1
Preparing...                ########################################### [100%]
        package netcat-1.10-883.2 (which is newer than netcat-0.7.1-1) is already installed
        file /usr/bin/netcat from install of netcat-0.7.1-1 conflicts with file from package netcat-1.10-883.2
        file /usr/share/man/man1/netcat.1.gz from install of netcat-0.7.1-1 conflicts with file from package netcat-1.10-883.2

[root@linux ~]# nc [IP|host] [port]
[root@linux ~]# nc -l -p [port]
参数：
-l，作为监听之用，亦即开启一个 port 来监听用户的联机。
-p，开启的这个 Port Number。

root@mail etc #nc -h
GNU netcat 0.7.0, a rewrite of the famous networking tool.
Basic usages:
connect to somewhere: nc [options] hostname port [port] ...
listen for inbound: nc -l -p port [options] [hostname] [port] ...
tunnel to somewhere: nc -L hostnameort -p port [options]

Mandatory arguments to long options are mandatory for short options too.
Options:
-c, --close close connection on EOF from stdin
-e, --exec=PROGRAM program to exec after connect
-g, --gateway=LIST source-routing hop point[s], up to 8
-G, --pointer=NUM source-routing pointer: 4, 8, 12, ...
-h, --help display this help and exit
-i, --interval=SECS delay interval for lines sent, ports scanned
-l, --listen listen mode, for inbound connects
-L, --tunnel=ADDRESS:PORT forward local port to remote address
-n, --dont-resolve numeric-only IP addresses, no DNS
-o, --output=FILE output hexdump traffic to FILE (implies -x)
-p, --local-port=NUM local port number
-r, --randomize randomize local and remote ports

/usr/bin/ 已经在path下面
vi vi .bash_profile
加入：
alias nc='netcat'

source /root/.bash_profile