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

Introducing regular expressions


You might have heard the term regular expression, or regex, before. For many people, a regular expression is something that seems very complicated, and is often plucked somewhere from the internet or a textbook, without fully grasping what it does.

 

 

While that is fine for completing a set task, understanding regular expressions better than the average systems administrator really allows you to differentiate yourself, both in creating scripts and working on the Terminal.

A nicely tailored regular expression can really help you keep your scripts short, simple, and robust to changes in the future.

What is a regular expression?

In essence, a regular expression is a piece of text that functions as a search pattern for other text. Regular expressions make it possible to easily say, for example, that I want to select all lines that contain a word that is five characters in length, or look for all files that end in .log.

An example might help with your understanding....