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

Introducing functions

Functions are blocks of code that exist in memory as named elements. These elements can be created within the shell environment, as well as within the script execution. When a command is issued at the command line, aliases are checked first and following this we check for a matching function name. To display the functions residing in your shell environment, you can use the following code:

$ declare -F

The output will vary depending on the distribution you are using and the number of functions you have created. On my Raspbian OS, the partial output is shown in the flowing screenshot:

Using the -f option, you can display the function and the associated definition. However, if we want to see just a single function definition, we can use the type command:

$ type quote

The previous code example will display the code block for the quote function, if it exists within your shell. We can see the output of this command in the following screenshot:

The quote function in bash inserts...