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  • Book Overview & Buying The Ultimate Linux Shell Scripting Guide
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The Ultimate Linux Shell Scripting Guide

The Ultimate Linux Shell Scripting Guide

By : Donald A. Tevault
4.8 (5)
Buy this Book
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The Ultimate Linux Shell Scripting Guide

The Ultimate Linux Shell Scripting Guide

4.8 (5)
By: Donald A. Tevault
Buy this Book

Overview of this book

Embark on a comprehensive journey through command shells with this hands-on manual. While Bash is a Linux staple, Z shell and PowerShell are rising stars, applicable to Linux, macOS, and Unix. Progress seamlessly through chapters, each building on the last, creating a solid foundation. Learn through a unique approach: concepts, examples, and interactive labs. These labs, nearly a hundred strong, form the core of experiential learning, essential for script creation. Focusing on Linux commands and their scripting applications, this manual is universally relevant across Linux and select Unix-like systems. It goes beyond theory, offering practical scripts for real-world Linux administration. Scripts are designed for manageability, aiding learning and troubleshooting. The goal is to nurture the ability to craft intelligent, functional shell scripts. While centered on Bash, this book offers a peek into the future with Z Shell and PowerShell, expanding your skills and adaptability. This book is systematically structured and engaging so that it will guide you to master command shells, equipping you for real-world Linux challenges.
Table of Contents (26 chapters)
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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
Getting Started with the Shell
Getting Started with the Shell
Understanding Shells
Finding Help with Shell Commands
Using a Text Editor to Create Shell Scripts
Understanding Compiled versus Interpreted Programming
Understanding root and sudo Privileges
Summary
Questions
Further Reading
Answers
Join our community on Discord!
2
Interpreting Commands
Interpreting Commands
Understanding the Structure of a Command
Executing Multiple Commands at Once
Running Commands Recursively
Understanding the Command History
Escaping and Quoting
Summary
Questions
Further Reading
Answers
Join our community on Discord!
3
Understanding Variables and Pipelines
Understanding Variables and Pipelines
Understanding Environmental Variables
Understanding Programming Variables
Understanding Pipelines
Summary
Questions
Further Reading
Answers
Join our community on Discord!
4
Understanding Input/Output Redirection
Understanding Input/Output Redirection
Introduction to Input/Output Redirection
Understanding stdout
Understanding stdin
Understanding stderr
Understanding tee
Hands-on Lab – Pipes, Redirectors, and find
Summary
Questions
Further Reading
Answers
Join our community on Discord!
5
Customizing the Environment
Customizing the Environment
Technical Requirements
Reviewing the Environmental Variables
Understanding Shell Sessions
Understanding the Configuration Files
Setting Shell Options from the Command-line
Understanding Aliases
Summary
Questions
Further Reading
Answers
Join our community on Discord!
6
Text-Stream Filters – Part 1
Text-Stream Filters – Part 1
Technical Requirements
Introduction to Text-Stream Filters
Using cat
Using tac
Using cut
Using paste
Using join
Using sort
Summary
Questions
Further Reading
Answers
Join our community on Discord!
7
Text Stream Filters – Part 2
Text Stream Filters – Part 2
Technical Requirements
Using expand
Using unexpand
Using nl
Using head
Using tail
Using Head And Tail Together
Using od
Using uniq
Using wc
Using fmt
Using split
Using tr
Using xargs
Using pr
Printing from the Command-line
Summary
Questions
Further Reading
Answers
Join our community on Discord!
8
Basic Shell Script Construction
Basic Shell Script Construction
Technical Requirements
Understanding Basic Shell Script Construction
Performing Tests
Understanding Subshells
Hands-on Lab – Testing Conditions
Understanding Scripting Variables
Understanding Array Variables
Understanding Variable Expansion
Understanding Command Substitution
Understanding Decisions and Loops
Understanding Exit Codes
More Information About echo
Looking at Some Real-World Examples
Summary
Questions
Further Reading
Answers
Join our community on Discord!
9
Filtering Text with grep, sed, and Regular Expressions
Filtering Text with grep, sed, and Regular Expressions
Technical Requirements
Understanding Regular Expressions
Understanding sed
Understanding grep
Using RegEx Helper Programs
Looking at Some Real-World Examples
Summary
Questions
Further Reading
Answers
Join our community on Discord!
10
Understanding Functions
Understanding Functions
Technical Requirements
Introduction to Functions
Defining a Function
Using Functions in Shell Scripts
Creating Function Libraries
Looking at Some Real-World Examples
Summary
Questions
Further Reading
Answers
Join our community on Discord!
11
Performing Mathematical Operations
Performing Mathematical Operations
Technical Requirements
Performing Integer Math with Expressions
Performing Integer Math with Integer Variables
Performing Floating Point Math with bc
Summary
Questions
Further Reading
Answers
Join our community on Discord!
12
Automating Scripts with here Documents and expect
Automating Scripts with here Documents and expect
Technical Requirements
Using here Documents
Automating Responses with expect
Summary
Questions
Further Reading
Answers
Join our community on Discord!
13
Scripting with ImageMagick
Scripting with ImageMagick
Technical Requirements
Converting Non-standard Filename Extensions
Installing ImageMagick
Resizing and Customizing Images
Batch-processing Image Files
Using Fred’s ImageMagick Scripts
Summary
Questions
Further Reading
Answers
Join our community on Discord!
14
Using awk – Part 1
Using awk – Part 1
Introducing awk
Understanding Patterns and Actions
Obtaining Input from Text Files
Obtaining Input from Commands
Summary
Questions
Further Reading
Answers
Join our community on Discord!
15
Using awk – Part 2
Using awk – Part 2
Technical Requirements
Basic awk Script Construction
Using Conditional Statements
Using a while Construct and Setting Variables
Using for loops and Arrays
Using Floating Point Math and printf
Working with Multi-Line Records
Summary
Questions
Further Reading
Answers
Join our community on Discord!
16
Creating User Interfaces with yad, dialog, and xdialog
Creating User Interfaces with yad, dialog, and xdialog
Technical Requirements
Creating a Graphical User Interface with yad
Creating User Interfaces with dialog and xdialog
Summary
Questions
Further Reading
Answers
Join our community on Discord!
17
Using Shell Script Options with getops
Using Shell Script Options with getops
Technical Requirements
Understanding the Need for getopts
Understanding getopt versus getopts
Using getopts
Looking at Real-world Examples
Summary
Questions
Further Reading
Answers
Join our community on Discord!
18
Shell Scripting for Security Professionals
Shell Scripting for Security Professionals
Technical Requirements
Simple Scripts for Auditing
Creating Simple Firewall Scripts
Searching for Existing Security-related Scripts
Summary
Questions
Further Reading
Answers
Join our community on Discord!
19
Shell Script Portability
Shell Script Portability
Technical Requirements
Running bash on Non-Linux Systems
Understanding POSIX compliance
Understanding the Differences Between Shells
Understanding Bashisms
Testing Scripts for POSIX Compliance
Summary
Questions
Further Reading
Answers
Join our community on Discord!
20
Shell Script Security
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Shell Script Security
Technical Requirements
Controlling Access to Your Scripts
Understanding SUID and SGID Considerations
Avoiding Sensitive Data Leakage
Understanding Command Injection with eval
Understanding Path Security
Summary
Questions
Further Reading
Answers
Join our community on Discord!
21
Debugging Shell Scripts
Debugging Shell Scripts
Technical Requirements
Understanding Common Scripting Errors
Using Shell Script Debugging Tools and Techniques
Summary
Questions
Further Reading
Answers
Join our community on Discord!
22
Introduction to Z Shell Scripting
Introduction to Z Shell Scripting
Technical Requirements
Introducing zsh
Installing zsh
Understanding the Unique Features of zsh Scripting
Using zsh Modules
Summary
Questions
Further Reading
Answers
Join our community on Discord!
23
Using PowerShell on Linux
Using PowerShell on Linux
Technical Requirements
Installing PowerShell on Linux and macOS
Reasons for Linux and Mac Admins to Learn PowerShell
Differences Between PowerShell Scripting and Traditional Linux/Unix Scripting
Viewing the Available PowerShell Commands
Getting Help with PowerShell Commands
Real-World Cross-Platform PowerShell Scripts
Summary
Further Reading
24
Other Books You May Enjoy
Other Books You May Enjoy
25
Index
Index

Understanding Path Security

The possibility—however remote it may be—exists that someone could plant a trojaned version of some system utility on your system, and then manipulate a user’s PATH setting so that the trojaned utility would be invoked, instead of the real one. The trojaned utility could do a variety of nasty things, such as exfiltrating sensitive data or performing a ransomware attack by encrypting important files. Before I show you a script, let’s see how this looks on the command-line. Let’s begin by showing you where the executable file for the normal ls command is located:

donnie@fedora-server:~$ which ls
alias ls='ls --color=auto'
    /usr/bin/ls
donnie@fedora-server:~$

We see that it’s located in the /usr/bin/ directory, as it should be. Now, let’s create a bogus ls, in the form of a script, and place it into the /tmp/ directory. Here’s the ls script:

#!/bin/bash
echo "This is a trojaned...

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