write

src: 6 More Unique Linux Utilities You Forgot About | by Tate Galbraith | Better Programming

This mighty little program might not do what you think it does at first glance. It has been available in Linux for decades and even dates back to Version 6 of Unix from 1975.

The write utility actually lets you send a message to other users on the same system. You can target any other logged in user and send them a message. Provide a username and you’ll be dropped into an interactive shell to write any text you want to them. Everything you type (including newlines) will appear on the targeted user’s console.

Here is a quick example:

write <username>

This will drop you into an interactive console to send messages to the corresponding user. Keep in mind this is a rather invasive way to message other users. They will immediately begin receiving the text you are entering right on their console. There will not be any warning or prompt for them to accept it. It’ll appear as if their terminal is haunted. They will also be unable to reply since this is a one-way communication.

Although there are better ways to handle inter-user messaging nowadays, this is a piece of computing history. I’m sure there could still be a few creative (and nefarious) uses for it today.

Check out the official man page here.