nc(netcat)被誉为网络工具中的“瑞士军刀”，体积虽小但功能强大，nc最简单的功能是端口扫描，这里我主要笔记一下它作为文件传输的妙用。

首先看一下帮助信息。

$ nc -h
OpenBSD netcat (Debian patchlevel 1.105-7ubuntu1)
This is nc from the netcat-openbsd package. An alternative nc is available
in the netcat-traditional package.
usage: nc [-46bCDdhjklnrStUuvZz] [-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]
    Command Summary:
        -4        Use IPv4
        -6        Use IPv6
        -b        Allow broadcast
        -C        Send CRLF as line-ending
        -D        Enable the debug socket option
        -d        Detach from stdin
        -h        This help text
        -I length    TCP receive buffer length
        -i secs        Delay interval for lines sent, ports scanned
        -j        Use jumbo frame
        -k        Keep inbound sockets open for multiple connects
        -l        Listen mode, for inbound connects
        -n        Suppress name/port resolutions
        -O length    TCP send buffer length
        -P proxyuser    Username for proxy authentication
        -p port        Specify local port for remote connects
            -q secs        quit after EOF on stdin and delay of secs
        -r        Randomize remote ports
        -S        Enable the TCP MD5 signature option
        -s addr        Local source address
        -T toskeyword    Set IP Type of Service
        -t        Answer TELNET negotiation
        -U        Use UNIX domain socket
        -u        UDP mode
        -V rtable    Specify alternate routing table
        -v        Verbose
        -w secs        Timeout for connects and final net reads
        -X proto    Proxy protocol: "4", "5" (SOCKS) or "connect"
        -x addr[:port]    Specify proxy address and port
        -Z        DCCP mode
        -z        Zero-I/O mode [used for scanning]
    Port numbers can be individual or ranges: lo-hi [inclusive]

端口扫描：

$ nc -z -v -n 127.0.0.1 20-100
...
Connection to 127.0.0.1 80 port [tcp/*] succeeded!
...

简单文件传输：

客户端：

$ nc -l 192.168.1.11 1234 > passwd.txt &

服务端：

$ nc 192.168.1.11 1234 < /etc/passwd

也可以是cat /etc/passwd | nc 192.168.1.11 1234

服务端ip是192.169.1.11，端口是1234

如此，当两台linux机器需要简单传输文件时，再好不过了～