| NC(1) | General Commands Manual | NC(1) | 
nc —
| nc | [ -46cDdFhklNnrStUuvz]
      [-Ccertfile]
      [-ename]
      [-Hhash]
      [-Ilength]
      [-iinterval]
      [-Kkeyfile]
      [-Mttl]
      [-mminttl]
      [-Olength]
      [-ostaplefile]
      [-Pproxy_username]
      [-psource_port]
      [-RCAfile]
      [-ssource]
      [-Tkeyword]
      [-wtimeout]
      [-Xproxy_protocol]
      [-xproxy_address[:port]]
      [destination] [port] | 
nc (or netcat) utility is
  used for just about anything under the sun involving TCP, UDP, or
  UNIX-domain sockets. It can open TCP connections, send
  UDP packets, listen on arbitrary TCP and UDP ports, do port scanning, and deal
  with both IPv4 and IPv6. Unlike
  telnet(1),
  nc scripts nicely, and separates error messages onto
  standard error instead of sending them to standard output, as
  telnet(1) does with some.
Common uses include:
The options are as follows:
-4nc to use IPv4 addresses only.-6nc to use IPv6 addresses only.-C
    certfile-c-D-d-e
    name-F-X to
      have nc perform connection setup with a proxy but
      then leave the rest of the connection to another program (e.g.
      ssh(1) using the
      ssh_config(5)
      ProxyUseFdpass option).-H
    hash-hnc help.-I
    length-i
    interval-K
    keyfile-knc to stay listening for another connection
      after its current connection is completed. It is an error to use this
      option without the -l option. When used together
      with the -u option, the server socket is not
      connected and it can receive UDP datagrams from multiple hosts.-lnc should listen for an
      incoming connection rather than initiate a connection to a remote host. It
      is an error to use this option in conjunction with the
      -p, -s, or
      -z options. Additionally, any timeouts specified
      with the -w option are ignored.-M
    ttl-m
    minttl-N-n-O
    length-o
    staplefile-P
    proxy_username-p
    source_portnc should use, subject
      to privilege restrictions and availability. It is an error to use this
      option in conjunction with the -l option.-R
    CAfile-r-S-s
    source-l option.-T
    keywordFor IPv4 TOS value keyword may be one of critical, inetcontrol, lowdelay, netcontrol, throughput, reliability, or one of the DiffServ Code Points: ef, af11 ... af43, cs0 ... cs7; or a number in either hex or decimal.
-tnc to send RFC 854 DON'T and WON'T
      responses to RFC 854 DO and WILL requests. This makes it possible to use
      nc to script telnet sessions.-U-u-s flag is
      given.-vnc give more verbose output.-w
    timeout-w flag
      has no effect on the -l option, i.e.
      nc will listen forever for a connection, with or
      without the -w flag. The default is no
    timeout.-X
    proxy_protocolnc should use the specified protocol
      when talking to the proxy server. Supported protocols are
      “4” (SOCKS v.4), “5” (SOCKS v.5) and
      “connect” (HTTPS proxy). If the protocol is not specified,
      SOCKS version 5 is used.-x
    proxy_address[:port]nc should connect to
      destination using a proxy at
      proxy_address and port. If
      port is not specified, the well-known port for the
      proxy protocol is used (1080 for SOCKS, 3128 for HTTPS).-znc should just scan for listening
      daemons, without sending any data to them. It is an error to use this
      option in conjunction with the -l option.destination can be a numerical IP address or
    a symbolic hostname (unless the -n option is given).
    In general, a destination must be specified, unless the
    -l option is given (in which case the local host is
    used). For UNIX-domain sockets, a destination is
    required and is the socket path to connect to (or listen on if the
    -l option is given).
port can be a specified as a numeric port
    number, or as a service name. Ports may be specified in a range of the form
    nn-mm. In general, a destination port must be specified, unless the
    -U option is given.
nc. On one console, start nc
  listening on a specific port for a connection. For example:
$ nc -l 1234nc is now listening on port 1234 for a
    connection. On a second console (or a second machine), connect to the
    machine and port being listened on:
$ nc 127.0.0.1 1234There should now be a connection between the ports. Anything typed
    at the second console will be concatenated to the first, and vice-versa.
    After the connection has been set up, nc does not
    really care which side is being used as a ‘server’ and which
    side is being used as a ‘client’. The connection may be
    terminated using an EOF (‘^D’).
Start by using nc to listen on a specific
    port, with output captured into a file:
$ nc -l 1234 >
  filename.outUsing a second machine, connect to the listening
    nc process, feeding it the file which is to be
    transferred:
$ nc -N host.example.com 1234 <
  filename.inAfter the file has been transferred, the connection will close automatically.
$ printf "GET / HTTP/1.0\r\n\r\n" | nc host.example.com 80
Note that this also displays the headers sent by the web server. They can be filtered, using a tool such as sed(1), if necessary.
More complicated examples can be built up when the user knows the format of requests required by the server. As another example, an email may be submitted to an SMTP server using:
$ nc localhost 25 << EOF HELO host.example.com MAIL FROM:<user@host.example.com> RCPT TO:<user2@host.example.com> DATA Body of email. . QUIT EOF
-z flag can be used to tell
  nc to report open ports, rather than initiate a
  connection. For example:
$ nc -z host.example.com 20-30 Connection to host.example.com 22 port [tcp/ssh] succeeded! Connection to host.example.com 25 port [tcp/smtp] succeeded!
The port range was specified to limit the search to ports 20 - 30.
Alternatively, it might be useful to know which server software is
    running, and which versions. This information is often contained within the
    greeting banners. In order to retrieve these, it is necessary to first make
    a connection, and then break the connection when the banner has been
    retrieved. This can be accomplished by specifying a small timeout with the
    -w flag, or perhaps by issuing a
    “QUIT” command to the server:
$ echo "QUIT" | nc host.example.com 20-30 SSH-1.99-OpenSSH_3.6.1p2 Protocol mismatch. 220 host.example.com IMS SMTP Receiver Version 0.84 Ready
$ nc -p 31337 -w 5 host.example.com
  42Open a TCP connection to port 443 of www.google.ca, and negotiate TLS. Check for a different name in the certificate for validation.
$ nc -v -c -e adsf.au.doubleclick.net
  www.google.ca 443Open a UDP connection to port 53 of host.example.com:
$ nc -u host.example.com
  53Open a TCP connection to port 42 of host.example.com using 10.1.2.3 as the IP for the local end of the connection:
$ nc -s 10.1.2.3 host.example.com
  42Create and listen on a UNIX-domain stream socket:
$ nc -lU
  /var/tmp/dsocketConnect to port 42 of host.example.com via an HTTP proxy at
    10.2.3.4, port 8080. This example could also be used by
    ssh(1); see the
    ProxyCommand directive in
    ssh_config(5) for more
    information.
$ nc -x10.2.3.4:8080 -Xconnect
  host.example.com 42The same example again, this time enabling proxy authentication with username “ruser” if the proxy requires it:
$ nc -x10.2.3.4:8080 -Xconnect
  -Pruser host.example.com 42-uz combination of flags will
  always report success irrespective of the target machine's state. However, in
  conjunction with a traffic sniffer either on the target machine or an
  intermediary device, the -uz combination could be
  useful for communications diagnostics. Note that the amount of UDP traffic
  generated may be limited either due to hardware resources and/or configuration
  settings.
| February 2, 2017 | NetBSD 9.4 |