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

Using regular expressions with egrep and sed


We have now discussed both regular expressions and globbing. As we saw, they were very similar, but still had differences to be aware of. In our examples for regular expressions, and a little for globbing, we have already seen how grep can be used.

In this part, we'll introduce another command, which is very handy when combined with regular expressions: sed (not to be confused with set). We'll start with some advanced uses for grep.

Advanced grep

We have already discussed a few popular options for grep to alter its default behavior: --ignore-case (-i), --invert-match (-v), and --word-regexp (-w). As a reminder here's what they do:

  • -i allows us to search case-insensitively
  • -v only prints lines that are not matched, instead of matched lines
  • -w only matches on full words that are surrounded by spaces and/or line anchors and/or punctuation marks

 

 

There are three other options we'd like to share with you. The first new option, --only-matching (-o) prints...