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

Positional parameters versus flags


We'll start this chapter off with a short recap on positional arguments. As you might remember from Chapter 8, Variables and User Input, we are able to use positional parameters to pass arguments to our scripts.

 

 

To put this simply, the following syntax is used:

bash script.sh argument1 argument2 ...

Inside the preceding (fictive) script.sh, we can then grab the values supplied by the user by looking at the positions the arguments are supplied in: $1 is the first argument, $2 is the second, and so on. Remember that $0 is a special argument, which relates to the name of the script: in this case, script.sh.

This approach is relatively simple, but also susceptible to errors. When you write this script, you need to check extensively for the input supplied by the user; did they give enough arguments, but not too many? Or, perhaps some arguments are optional, so a few combinations are possible? All these things need to be considered and, if possible, dealt with...