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 11


  1. How does an if-then(-else) statement end? With the reverse of the word if: fi
  2. How can we use regular expression search patterns in a conditional evaluation? By employing the =~ comparison symbol. For example: [[ ${var} =~ [[:digit:]] ]]
  3. Why do we need the elif keyword? If we want to sequentially test for more than one condition, we can use else if (elif).
  4. What is nesting? Using an if-then-else statement or loop within another if-then-else statement or loop.
  5. How can we get information about how to use shell builtins and keywords? By using the command help, followed by the builtin or keyword we want information about. For example: help [[
  6. What is the opposite keyword of while?until. A while loop runs until the condition is no longer true, an until loop runs until the condition is no longer false.
  7. Why would we choose the for loop over the while loop?for is more powerful and has many convenient shorthand syntaxes which would be hard or unreadable with while.
  8. What is brace expansion and on which characters can we use it? Brace expansion allows us to write very short code, which generates a whitespace delimited list based on ASCII characters. For example: {1..10} prints the numbers 1 through 10, with spaces in between. We can also use this for uppercase or lowercase letters, or any range in the ASCII character set.
  9. Which two keywords allows us to have more granular control over loops?break and continue. break stops the current loop, while continue jumps to the next iteration in the loop.
  1. If we are nesting loops, how can we employ loop control to influence outer loops from an inner loop? By adding a number higher than 1 to the break or continue keyword. Example: break 2 exits from both the inner and one outer loop.