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

Function libraries


When you get to this part of the book, you'll have seen well over 50 example scripts. Many of these scripts have some shared components: input checking, error handling, and setting the current working directory have been used in multiple scripts. This code doesn't really change; perhaps the comments or echoes were slightly different, but in reality it's just duplicated code. Pair this with the problem of having to define functions at the top of your script (or, at the very least, before you start using them) and your maintainability is beginning to suffer. Luckily for us all, there is a great solution for this: creating your own function library!

Source

The idea of a function library is that you define functions that are shared between different scripts. These are repeatable, generic functions that do not care too much about the specific script to work. When you create a new script, the first thing you'll do, right after the header, is include the function definitions from...