If there is one thing that sets the Linux CLI apart from the GUI, then it is the use of shell scripts. Put simply, a script is a set of commands that can be run on the CLI. You can save loads of time by using scripts to do repetitive tasks. But of course the the first thing you need to use a shell script is knowing how to write and use it in the first place.
Advanced Bash-Scripting Guide is a free, straight to the point online scripting guide that will teach you the mechanics of scripting for Bash, the default CLI on Ubuntu.
“This tutorial assumes no previous knowledge of scripting or programming, but progresses rapidly toward an intermediate/advanced level of instruction . . . all the while sneaking in little nuggets of UNIX wisdom and lore. It serves as a textbook, a manual for self-study, and a reference and source of knowledge on shell scripting techniques.
“The exercises and heavily-commented examples invite active reader participation, under the premise that the only way to really learn scripting is to write scripts.This book is suitable for classroom use as a general introduction to programming concepts.”
The guide is divided into 5 parts starting from introduction to scripting right up to advanced topics that put smiles on the face of every hardcore geek :-). In case you were wondering how you would ever master the art of shell scripting to add some extra power to your Linux box and also to show off among your friends, then this guide is what you need. Read it and start writing your own scripts asap!