Unix : the “script” command

The script command is a must for any unix sysadmin.

Once invoked, it will faithfully write anything you typed as well as any output generated in your terminal into a file of your choice (defaults to “typescript”).

This is great when you want to document everything you did on a specific server, for example.
spaghetti:~$ script
Script started, file is typescript

When launched, you don’t see anything, but everything displayed goes to a file as well as the terminal.

As usual see the man page for details (like appending instead of creating a new file, launching another command instead of your default shell, and so on)