Book Image

Mastering Linux Shell Scripting - Second Edition

By : Mokhtar Ebrahim, Andrew Mallett
5 (1)
Book Image

Mastering Linux Shell Scripting - Second Edition

5 (1)
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.

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Table of Contents (17 chapters)
Preface
Preface
Who this book is for
What this book covers
To get the most out of this book
Get in touch
Free Chapter
1
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
2
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
3
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
4
Creating Code Snippets
Creating Code Snippets
Technical requirements
Abbreviations
Using code snippets
Creating snippets using VS Code
Summary
Questions
Further reading
5
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
6
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
7
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
8
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
9
Automating Apache Virtual Hosts
Automating Apache Virtual Hosts
Technical requirements
Apache name-based Virtual Hosts
Automating virtual host creation
Summary
Questions
Further reading
10
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
11
Regular Expressions
Regular Expressions
Technical requirements
Regular expression engines
Defining BRE patterns
Defining ERE patterns
Using grep
Summary
Questions
Further reading
12
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
13
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
14
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
15
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
16
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AWK variables

We saw how to use data fields such as $1 and $2. Also, we saw the NR field, which holds the number of processed lines, but there are more built-in variables that AWK offers to simplify work more and more.

  • FIELDWIDTHS: Specifies the field width
  • RS: Specifies the record separator
  • FS: Specifies the field separator
  • OFS: Specifies the output separator, which is a space by default
  • ORS: Specifies the output separator
  • FILENAME: Holds the processed file name
  • NF: Holds the line being processed
  • FNR: Holds the record which is processed
  • IGNORECASE: Ignores character case

These variables can help you a lot in many cases. Let's assume that we have the following file:

John Doe
15 back street
(123) 455-3584
    
Mokhtar Ebrahim
10 Museum street
(456) 352-3541

We can say that we have two records for two persons and each record contains three fields. Let's assume that...

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