Nowadays, most computer users are only familiar with the Graphical User Interface (GUI) and think that Command Line Interface (CLI) is an old-fashioned way to interact with computer. This is not true, because command line interface is expressive way to interact with computer, just like writing letter or message to our friends. It's been said that:

graphical user interfaces make easy tasks easy, while command line interfaces make difficult tasks possible

So, learning command line interface is important if you want to get the most out of Linux operating system. Linux command line is a great tool because we can perform a lot of tasks there. There are many references to learning command line interface. One of them is an eBook I'll post here.

This book is entitled "The Linux Command Line" written by William E. Shotts. This book contains 522 pages and divided into five parts:
Part 1: Introduction
Tells some story related with command line interface.

Part 2: Learning The Shell
Starts the exploration of the basic language of the command line including such things as the structure of commands, file system navigation, command line editing, and finding help and documentation for commands.

Part 3: Configuration And The Environment
Covers editing configuration files that control the computer's operation from the command line.

Part 4: Common Tasks And Essential Tools
Explores many of the ordinary tasks that are commonly performed from the command line. Unix-like operating systems, such as Linux, contain many “classic” command line programs that are used to perform powerful operations on data.

Part 5: Writing Shell Scripts
Introduces shell programming, an admittedly rudimentary, but easy to learn, technique for automating many common computing tasks. By learning shell programming, you will become familiar with concepts that can be applied to many other programming languages.

Well, if you want to learn Linux command line interface to get the most out of it, please download this book by clicking the below link:

Download eBook: The Linux Command Line

Regards :)