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Mastering Linux Shell Scripting

By : Mokhtar Ebrahim, Andrew Mallett

3.8 (23)

Mastering Linux Shell Scripting

3.8 (23)

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.

Preface

Preface

Who this book is for

What this book covers

To get the most out of this book

Get in touch

Free Chapter

The What and Why of Scripting with Bash

The What and Why of Scripting with Bash

Technical requirements

Types of Linux shells

What is bash scripting?

The bash command hierarchy

Preparing text editors for scripting

Creating and executing scripts

Declaring variables

Variable scope

Command substitution

Debugging your scripts

Summary

Questions

Further reading

Creating Interactive Scripts

Creating Interactive Scripts

Technical requirements

Using echo with options

Basic script using read

Script comments

Enhancing scripts with read prompts

Limiting the number of entered characters

Controlling the visibility of the entered text

Passing options

Try to be standard

Enhancing learning with simple scripts

Summary

Questions

Further reading

Conditions Attached

Conditions Attached

Technical requirements

Simple decision paths using command-line lists

Verifying user input with lists

Using the test shell built-in

Creating conditional statements using if

Extending if with else

Test command with the if command

More conditions with elif

Using case statements

Recipe – building a frontend with grep

Summary

Questions

Further reading

Creating Code Snippets

Creating Code Snippets

Technical requirements

Abbreviations

Using code snippets

Creating snippets using VS Code

Summary

Questions

Further reading

Alternative Syntax

Alternative Syntax

Technical requirement

Recapping the test command

Providing parameter defaults

When in doubt – quote!

Advanced tests using [[

Arithmetic operations using ((

Summary

Questions

Further reading

Iterating with Loops

Iterating with Loops

Technical requirement

for loops

Advanced for loops

The IFS

Counting directories and files

C-style for loops

Nested loops

Redirecting loop output

while loops and until loops

Reading input from files

Creating operator menus

Summary

Questions

Further reading

Creating Building Blocks with Functions

Creating Building Blocks with Functions

Technical requirements

Introducing functions

Passing parameters to functions

Variable scope

Returning values from functions

Recursive functions

Using functions in menus

Summary

Questions

Further reading

Introducing the Stream Editor

Introducing the Stream Editor

Technical requirements

Using grep to display text

Understanding the basics of sed

Other sed commands

Multiple sed commands

Summary

Questions

Further reading

Automating Apache Virtual Hosts

Automating Apache Virtual Hosts

Technical requirements

Apache name-based Virtual Hosts

Automating virtual host creation

Summary

Questions

Further reading

AWK Fundamentals

AWK Fundamentals

Technical requirements

The history behind AWK

Displaying and filtering content from files

AWK variables

Conditional statements

Formatting output

Further filtering to display users by UID

AWK control files

Summary

Questions

Further reading

Regular Expressions

Regular Expressions

Technical requirements

Regular expression engines

Defining BRE patterns

Defining ERE patterns

Using grep

Summary

Questions

Further reading

Summarizing Logs with AWK

Summarizing Logs with AWK

Technical requirements

The HTTPD log file format

Displaying data from web logs

Displaying the highest ranking IP address

Displaying the browser data

Working with email logs

Summary

Questions

Further reading

A Better lastlog with AWK

A Better lastlog with AWK

Technical requirements

Using AWK ranges to exclude data

Conditions based on the number of fields

Manipulating the AWK record separator to report on XML data

Summary

Questions

Further reading

Using Python as a Bash Scripting Alternative

Using Python as a Bash Scripting Alternative

Technical requirements

What is Python?

Saying Hello World the Python way

Pythonic arguments

Supplying arguments

Counting arguments

Significant whitespace

Reading user input

Using Python to write to files

String manipulation

Summary

Questions

Further reading

Assessments

Assessments

Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter 6

Chapter 7

Chapter 8

Chapter 9

Chapter 10

Chapter 11

Chapter 12

Chapter 13

Chapter 14

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Arithmetic operations using ((

When using bash and some other advanced shells, we can make use of the (( )) notation to simplify mathematical operations with scripts.

Simple math

The double parenthesis construct in bash allows for arithmetic expansion. Using this in the simplest format, we can easily carry out integer arithmetic. This becomes a replacement for the let built-in. The following examples show the use of the let command and the double parenthesis to achieve the same result:

$ a=(( 2 + 3 ))
$ let a=2+3

In both cases, the a parameter is populated with the sum of 2 + 3. If you want to write it on a shell script, you need to add a dollar sign before the parentheses:

#!/bin/bash
echo $(( 2 + 3 ))

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