Book Image

Learn Linux Shell Scripting – Fundamentals of Bash 4.4

By : Sebastiaan Tammer
Book Image

Learn Linux Shell Scripting – Fundamentals of Bash 4.4

By: Sebastiaan Tammer

Overview of this book

Shell scripts allow us to program commands in chains and have the system execute them as a scripted event, just like batch files. This book will start with an overview of Linux and Bash shell scripting, and then quickly deep dive into helping you set up your local environment, before introducing you to tools that are used to write shell scripts. The next set of chapters will focus on helping you understand Linux under the hood and what Bash provides the user. Soon, you will have embarked on your journey along the command line. You will now begin writing actual scripts instead of commands, and will be introduced to practical applications for scripts. The final set of chapters will deep dive into the more advanced topics in shell scripting. These advanced topics will take you from simple scripts to reusable, valuable programs that exist in the real world. The final chapter will leave you with some handy tips and tricks and, as regards the most frequently used commands, a cheat sheet containing the most interesting flags and options will also be provided. After completing this book, you should feel confident about starting your own shell scripting projects, no matter how simple or complex the task previously seemed. We aim to teach you how to script and what to consider, to complement the clear-cut patterns that you can use in your daily scripting challenges.
Table of Contents (24 chapters)
Title Page
About Packt
Contributors
Preface
Free Chapter
1
Introduction
Index

What is a variable?


Variables are a standard building block used in many (if not all) programming and scripting languages. Variables allow us to store information, so we can reference and use it later, often multiple times. We can, for example, use the textvariable variable to store the sentence This text is contained in the variable. In this case, the variable name of textvariable is referred to as the key, and the content of the variable (the text) is referred to as the value, in the key-value pair that makes up the variable.

In our program, we always reference the textvariable variable when we need the text. This might be a bit abstract now, but we're confident that after seeing the examples in the rest of the chapter, the usefulness of variables will become clear.

We've actually already seen Bash variables in use. Remember, in Chapter 4, The Linux Filesystem, we looked at both the BASH_VERSION and PATH variables. Let's see how we can use variables in shell scripting. We'll take our hello...