-4      Forces nc to use IPv4 addresses only.

-6      Forces nc to use IPv6 addresses only.

-D      Enable debugging on the socket.

-d      Do not attempt to read from stdin.

-h      Prints out nc help.

-i interval
        Specifies a delay time interval between lines of text sent and received.  Also causes a delay time
        between connections to multiple ports.

-k      Forces nc to stay listening for another connection after its current connection is completed.  It
        is an error to use this option without the -l option.

-l      Used to specify that nc 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.

-n      Do not do any DNS or service lookups on any specified addresses, hostnames or ports.

-P proxy_username
        Specifies a username to present to a proxy server that requires authentication.  If no username is
        specified then authentication will not be attempted.  Proxy authentication is only supported for
        HTTP CONNECT proxies at present.

-p source_port
        Specifies the source port nc should use, subject to privilege restrictions and availability.  It is
        an error to use this option in conjunction with the -l option.

-q      after EOF on stdin, wait the specified number of seconds and then quit. If seconds is negative,
        wait forever.

-r      Specifies that source and/or destination ports should be chosen randomly instead of sequentially
        within a range or in the order that the system assigns them.

-S      Enables the RFC 2385 TCP MD5 signature option.

-s source_ip_address
        Specifies the IP of the interface which is used to send the packets.  It is an error to use this
        option in conjunction with the -l option.

-T ToS  Specifies IP Type of Service (ToS) for the connection.  Valid values are the tokens “lowdelay”,
        “throughput”, “reliability”, or an 8-bit hexadecimal value preceded by “0x”.

-C      Send CRLF as line-ending

-t      Causes nc 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      Specifies to use Unix Domain Sockets.

-u      Use UDP instead of the default option of TCP.

-v      Have nc give more verbose output.

-w timeout
        If a connection and stdin are idle for more than timeout seconds, then the connection is silently
        closed.  The -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_protocol
        Requests that nc 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]
        Requests that nc should connect to hostname 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).

-z      Specifies that nc 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.