How to study source codes: Adding a keylogger to the Bash

At the The Cuckoo's Egg book, the writer explains how he were tracking a hacker at 1986. One of his ideas was adding a logger to the Shell executable and see every keystroke he pushes. In this Video, I'll try to add the same thing to the Bash and I will show you how you can study a source code and find your way around it.