Learning Linux Shell Scripting

Ganesh Sanjiv Naik

• Publisher: Packt Publishing
• Year: 2015
• ISBN:
  9781785286216
• Edition: 1
• Topic: Computer Science
• Subtopic: Operating Systems
• Index: Computer Science

Unleash the power of shell scripts to solve real-world problems by breaking through the practice of writing tedious code

About This Book

• Learn how to efficiently and effectively build shell scripts and develop advanced applications with this handy book
• Develop high quality and efficient solutions by writing professional and real-world scripts, and debug scripts by checking and shell tracing
• A step-by-step tutorial to automate routine tasks by developing scripts from a basic level to very advanced functionality

Who This Book Is For

This book is ideal for those who are proficient at working with Linux and who want to learn about shell scripting to improve their efficiency and practical skills. By the end of this book, you will be able to confidently use your own shell scripts in the real world.

What You Will Learn

• Familiarize yourself with the various text filtering tools available in Linux
• Combine the fundamental text and file processing commands to process data and automate repetitive tasks
• Understand expressions and variables and how to use them practically
• Automate decision-making and save a lot of time and effort of revisiting code
• Get to grips with advanced functionality such as using traps and signals and using dialogs to develop screens
• Start up a system and customize a Linux system
• Take an in-depth look at regular expressions and pattern matching to understand the capabilities of scripting

In Detail

Linux is the one of the most powerful and universally adopted OSes. Shell is a program that gives the user direct interaction with the operating system. Scripts are collections of commands that are stored in a file. The shell can read this file and act on the commands as if they were typed on the keyboard. Shell scripting is used to automate day-to-day administration, and for testing or product development tasks.

This book covers Bash, GNU Bourne Again SHell, preparing you to work in the exciting world of Linux shell scripting. We start with an introduction to the Shell environment and explain basic commands used in Shell. Next we move on to check, kill, and control the execution of processes in Linux OS. Further, we teach you about the filter tools available in Linux and explain standard output and standard errors devices.

Then we will ensure you understand Shell's interpretation of commands and get a firmer grasp so you use them in practice. Next, you'll experience some real-world essentials such as debugging and perform Shell arithmetic fluently. Then you'll take a step ahead and learn new and advanced topics in Shell scripting, such as starting up a system and customizing a Linux system. Finally, you'll get to understand the capabilities of scripting and learn about Grep, Stream Editor, and Awk.

Style and approach

This practical book will go from the very basics of shell scripting to complex, customized automation. The idea behind this book is to be as practical as possible and give you the look and feel of what real-world scripting is like.

Learning Linux Shell Scripting

---

Table of Contents

Learning Linux Shell Scripting

Credits

About the Author

Acknowledgments

About the Reviewers

www.PacktPub.com

Support files, eBooks, discount offers, and more

Why subscribe?

Free access for Packt account holders

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the color images of this book

Errata

Piracy

Questions

1. Getting Started and Working with Shell Scripting

Comparison of shells

Tasks done by shell

Working in shell

Learning basic Linux commands

Our first script – Hello World

Compiler and interpreter – difference in process

When not to use scripts

Various directories

Working more effectively with shell – basic commands

Working with permissions

Changing file permissions

Command chmod

Technique one – the symbolic method

Technique two – the numeric method

Setting umask

Setuid

Setgid

Sticky bit

Summary

2. Drilling Deep into Process Management, Job Control, and Automation

Introducing process basics

Monitoring processes using ps

Process management

Process monitoring tools – top, iostat, and vmstat

Understanding "at"

Understanding "crontab"

Summary

3. Using Text Processing and Filters in Your Scripts

Text filtering tools

Head and tail

The diff command

The cut command

The paste command

The join command

The uniq command

The comm command

The tr command

IO redirection

File descriptors

Redirection

Brace expansion

Pattern matching with the vi editor

Pattern searching using grep

Summary

4. Working with Commands

Learning shell interpretation of commands

Checking and disabling shell internal commands

The exit status

Command substitution

Command separators

Command1; command2

Command grouping

Logical operators

Command1 & command2

Command1 && command2

Command1 || command2

Pipes

Summary

5. Exploring Expressions and Variables

Understanding variables

Working with environment variables

The local variable and its scope

Exporting variables

Working with read-only variables

Working with command line arguments (special variables, set and shift, getopt)

Understanding set

Understanding shift

Resetting positional parameters

Understanding getopts

Understanding default parameters

Working with arrays

Creating an array and initializing it

Accessing array values

Summary

6. Neat Tricks with Shell Scripting

Interactive Shell scripts – reading user input

Summarizing the read command with options

The here document and the << operator

The here operator with the sort command

The here operator with the wc command

The utility ed and here operator

A script for sending messages to all logged-in users

Using the << here operator for FTP usage and data transfer

Turning off variable substitution

The here string and the <<< operator

File handling

Introducing file handling

Using exec to assign file descriptor (fd) to file

Understanding the opening, writing, and closing of a file

Understanding reading from a file

Understanding reading and writing to a file

Using command read on file descriptor (fd)

Reading from one file and writing to another file

Displaying the file descriptor information from the /proc folder

File handling – reading line by line

Executing the command and storing the results in a file

Summarizing usage of the exec command

Debugging

Debugging mode – di...

Table of contents

• Learning Linux Shell Scripting