使用netcat(瑞士军刀)进行文件传输

$ 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]

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

$ nc -l 192.168.1.11 1234 > passwd.txt &

$ nc 192.168.1.11 1234 < /etc/passwd

cat /etc/passwd | nc 192.168.1.11 1234