nc: invalid option -- 4

[kehao95]

Hi, I couldn't run the nc command as expected.
It seems I have a different version of netcat.
I am using macOS Sierra 10.12.5

$ echo -n "black" | nc -4u -w0 localhost 1738

nc: invalid option -- 4
Try `nc --help' for more information.

$ nc --version

netcat (The GNU Netcat) 0.7.1
Copyright (C) 2002 - 2003  Giovanni Giacobbi

This program comes with NO WARRANTY, to the extent permitted by law.
You may redistribute copies of this program under the terms of
the GNU General Public License.
For more information about these matters, see the file named COPYING.

Original idea and design by Avian Research <[email protected]>,
Written by Giovanni Giacobbi <[email protected]>.

$ nc --help

GNU netcat 0.7.1, 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 hostname:port -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
  -s, --source=ADDRESS       local source address (ip or hostname)
  -t, --tcp                  TCP mode (default)
  -T, --telnet               answer using TELNET negotiation
  -u, --udp                  UDP mode
  -v, --verbose              verbose (use twice to be more verbose)
  -V, --version              output version information and exit
  -x, --hexdump              hexdump incoming and outgoing traffic
  -w, --wait=SECS            timeout for connects and final net reads
  -z, --zero                 zero-I/O mode (used for scanning)

Remote port number can also be specified as range.  Example: '1-1024'

[kehao95]

And this can be solved by using following command:

echo -n "green" | nc -u -c localhost 1738

[poige]

In fact there's no need for nc at all if one's using bash:

bash -c 'echo -n black > /dev/udp/localhost/1738'

[chaitanyarahalkar]

And this can be solved by using following command:

echo -n "green" | nc -u -c localhost 1738

Thanks a lot. I was facing the same issue!