Thanks so much your book review, Fabien! I wrote "Efficient Linux at the Command Line" because I kept meeting Linux/Unix users (over the past 30 years) who had learned the command line mostly by trial and error. They could use Linux OK for their jobs, but they didn't know the underlying concepts and had all sorts of inefficiencies or superstitions. I'd spend a few minutes with these users, and their speed at the command line would literally double, just from showing them job control, CDPATH, the directory stack, and other features they'd missed. I'm glad you enjoyed the book.