OpenBSD netcat demystified

Owing to its versatile functionalities, netcat earns the reputation as “TCP/IP Swiss army knife”. For example, you can create a simple chat app using netcat:

(1) Open a terminal and input following command: 

  1. # nc -l 3003

This means a netcat process will listen on 3003 port in this machine (the IP address of current machine is 192.168.35.176).

(2) Connect aforemontioned netcat process in another machine, and send a greeting: 

  1. # nc 192.168.35.176 3003
  2. hello

Then in the first machine’s terminal, you will see the “hello” text: 

  1. # nc -l 3003
  2. hello

A primitive chatroom is built successfully. Very cool! Isn’t it? I think many people can’t wait to explore more features of netcatnow. If you are among them, congratulations! This tutorial may be the correct place for you.

In the following parts, I will delve into OpenBSD‘s netcatcode to give a detailed anatomy of it. The reason of picking OpenBSD‘s netcat rather than others’ is because its code repository is small (~2000 lines of code) and neat. Furthermore, I also hope this little book can assist you learn more socket programming knowledge not just grasping usage of netcat.

We’re all set. Let’s go!