Book Image

Mastering Linux Shell Scripting - Second Edition

By : Mokhtar Ebrahim, Andrew Mallett
5 (1)
Book Image

Mastering Linux Shell Scripting - Second Edition

5 (1)
By: Mokhtar Ebrahim, Andrew Mallett

Overview of this book

In this book, you’ll discover everything you need to know to master shell scripting and make informed choices about the elements you employ. Grab your favorite editor and start writing your best Bash scripts step by step. Get to grips with the fundamentals of creating and running a script in normal mode, and in debug mode. Learn about various conditional statements' code snippets, and realize the power of repetition and loops in your shell script. You will also learn to write complex shell scripts. This book will also deep dive into file system administration, directories, and system administration like networking, process management, user authentications, and package installation and regular expressions. Towards the end of the book, you will learn how to use Python as a BASH Scripting alternative. By the end of this book, you will know shell scripts at the snap of your fingers and will be able to automate and communicate with your system with keyboard expressions.
Table of Contents (17 chapters)

Returning values from functions

Whenever we have statements that are printed on the screen within the function, we can see their result. However, lots of times we will want the function to populate a variable within the script and not display anything. In this case, we use return in the function. This is especially important when we are gaining input from users. We may prefer the case to translate the input to a known case to make the condition testing easier. Embedding the code in a function allows it to be used many times within a script.

The following code shows how we can achieve this by creating the to_lower function:

to_lower () 
{ 
    input="$1" 
    output=$( echo $input | tr [A-Z] [a-z]) 
return $output 
} 

Stepping through the code, we can begin to understand the operation of this function:

  • input="$1": This is more for ease than anything else; we...