Book Image

Mastering Linux Shell Scripting

By : Andrew Mallett
Book Image

Mastering Linux Shell Scripting

By: Andrew Mallett

Overview of this book

Shell scripting is a quick method to prototype a complex application or a problem by automating tasks when working on Linux-based systems. Using both simple one-line commands and command sequences complex problems can be solved with ease, from text processing to backing up sysadmin tools. In this book, you’ll discover everything you need to know to master shell scripting and make informed choices about the elements you employ. 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. Implement functions and edit files using the Stream Editor, script in Perl, program in Python – as well as complete coverage of other scripting languages to ensure you can choose the best tool for your project.
Table of Contents (21 chapters)
Mastering Linux Shell Scripting
About the Author
About the Reviewer

Returning values from functions

Whenever we have statements that are printed on the screen within the function, we can see their result. However, many 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:

function to_lower ()
    output=$(tr [A-Z] [a-z] <<<"$input")
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 assign the first input parameter to a named variable input.

  • output=$(tr [A-Z] [a-z] <<< "$input"): This is the main engine...