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

The getopts shell builtin


Now the real fun begins! In this second part of this chapter, we'll explain the getopts shell builtin. The getopts command is used in the beginning of your script to get the options you supplied in the form of flags. It has a very specific syntax that will seem confusing at first, but, once we've looked at it fully, it should not be too complicated for you to understand.

Before we dive in, though, we'll need to discuss two things:

  • The difference between getopts and getopt
  • Short versus long options

As stated, getopts is a shell builtin. It is available in both the regular Bourne shell (sh) and in Bash. It originated around 1986, as a replacement for getopt, which was created sometime before 1980.

In contrast to getopts, getopt is not built into the shell: it is a standalone program that has been ported to many different Unix and Unix-like distributions. The main differences between getopts and getopt are as follows:

  • getopt does not handle empty flag arguments well; getopts...