How can I record what I just did?

When you are doing a complex analysis, you will often want to keep a record of the commands you used. You can do this with the tools you have already seen:

1. Run history.
2. Pipe its output to tail -n 10 (or however many recent steps you want to save).
3. Redirect that to a file called something like figure-5.history.

This is better than writing things down in a lab notebook because it is guaranteed not to miss any steps. It also illustrates the central idea of the shell: simple tools that produce and consume lines of text can be combined in a wide variety of ways to solve a broad range of problems.