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

Parameter expansion


In this second-to-last chapter, with the final chapter being tips and tricks, we will deal with a very cool feature of Bash: parameter expansion.

We'll begin with a few notes on terminology. First of all, what's considered parameter expansion in Bash deals with more than just parameters/arguments supplied to a script: all special operations we'll be discussing in this chapter are applicable to Bash variables. In the official Bash manual page (man bash), these are all referred to as parameters.

For positional arguments to scripts, or even options with arguments, this makes sense. However, once we enter the territory of constants defined by the script creator, the distinction between a constant/variable and a parameter gets a bit muddy. This is of no further consequence; just remember that when you see the word parameter in a man page, it might be referring to variables in general.

Secondly, people tend to be a bit confused about the terms parameter expansion and parameter...