tlcl means The Linux Command Line. It is a nice book to learn about Linux. It was written by Wlliam Shotts. I totally recommend it. Besides it's free!
The official page of the book is here http://linuxcommand.org/tlcl.php.
This humble github repo contains all of the scripts from the book (starting from chapter 20).
The purpose is that anybody can clone this repo and follow the scripts from the book in their own computer.