Second print edition of "The Linux Command Line: A Complete Introduction" by William Shotts is now available in stores
The book was initially published in 2009 and has been gradually updated and modernized since. It covers subjects from What is the Shell to Regular Expressions, Text Processing and many other subjects.
The Internet Edition of the book is licensed under the CreativeCommons license by-nc-nd.
You can supposedly buy the paper edition of the book "wherever fine books are sold".