Ubuntu – Sending a simple TCP message using Netcat

You can look at the packages' descriptions using apt-cache show. They say it all:

$ apt-cache show netcat-traditional 
...
 This is the "classic" netcat, written by *Hobbit*. It lacks many
 features found in netcat-openbsd.
...
$ apt-cache show netcat-openbsd 
...
 This package contains the OpenBSD rewrite of netcat, including support
 for IPv6, proxies, and Unix sockets.
...

So the significant differences are as stated. The OpenBSD rewrite supports IPv6, proxies, and Unix sockets, which the traditional implementation lacks. In practice, if you don't need any of these, you won't notice a difference.

You can do something like this.

Assume Alice is the server. She types:

mawk -W interactive '$0="Alice: "$0' | nc -l -p <port_number> <ip_of_alice>

Then Bob connects to that server. He types:

mawk -W interactive '$0="Bob: "$0' | nc <ip_of_alice> <port_number>

The mawk lines just adds the prepending name of the person to the "chat". We need -W interactive to set unbuffered writes to stdout and line buffered reads from stdin.

Now Alice types Hi Bob and sees:

Hi Bob

Bob sees:

Alice: Hi Bob

Bob types Hi Alice and sees:

Alice: Hi Bob
Hi Alice

Alice sees:

Hi Bob
Bob: Hi Alice