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

Chapter 16


  1. What is parameter substitution?Nothing more than the run-time substitution of the variable name with its value at that moment.
  2. How can we include default values for our defined variables? With the ${variable:-value} syntax, where variable is the name and value the default value. This will only be used if the value is null or empty ('').
  3. How can we use parameter expansion to handle missing parameter values?While you would normally use an if [[ -z ${variable} ]]; then, parameter expansion allows you to use the following syntax to generate an error message and exit 1: ${1:?Name not supplied!}
  4. What does ${#*} do?It is the same as $#, which we use to determine the number of arguments passed to our shell script. The general ${#name} syntax allows us to get the length of the value of the name variable.
  5. How does pattern substitution work when talking about parameter expansions?Pattern substitution allows us to take the value of a variable and modify it slightly, by doing a search/replace for a pattern.
  6. How is pattern removal related to pattern substitution? Removing a pattern is the same as replacing a pattern with nothing. With pattern removal, we get the added flexibility of search both from the beginning of the text (prefix) and from the end (suffix). Pattern removal is great when working with file paths.
  7. What types of case modifications can we perform?
    • Lowercasing
    • Upercasing
    • Reversing the casing
  8. Which two things can we use to get a substring from a variables' value?We need an offset, or a lenght, or  the combination of both (most common).