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

Pipes


Finally, the moment we've all been waiting for: pipes. These near-magical constructs are used so much in Linux/Bash that everyone should know about them. Anything more complex than a single command will almost always use pipes to get to the solution.

And now the big reveal: all a pipe really does is connect the stdout of a command to the stdin of another command.

Wait, what?!

Binding stdout to stdin

Yes, that is really all that happens. It might be a little disappointing, now that you know all about input and output redirection. However, just because the concept is simple, that doesn't mean that pipes are not extremely powerful and very widely used.

Let's look at an example that shows how we can replace input/output redirection with a pipe:

reader@ubuntu:/tmp$ echo 'Fly into the distance' > file
reader@ubuntu:/tmp$ grep 'distance' < file
Fly into the distance
reader@ubuntu:/tmp$ echo 'Fly into the distance' | grep 'distance'
Fly into the distance

For the normal redirection, we first...