What is linux shell scripting pdf

Shell Scripting Tutorial: How to Create Shell Script in Linux/Unix

Updated October 7, 2021

Shell Scripting

Shell Scripting is an open-source computer program designed to be run by the Unix/Linux shell. Shell Scripting is a program to write a series of commands for the shell to execute. It can combine lengthy and repetitive sequences of commands into a single and simple script that can be stored and executed anytime which, reduces programming efforts.

This Shell Scripting tutorial helps to learn a basic understanding of the Linux/Unix shell scripting program to advanced concepts of Shell Scripting. This Shell Script tutorial designed for beginners and professionals who want to learn What is Shell Scripting? How shell scripting works, types of shell, and more.

What is Shell?

Shell is a UNIX term for an interface between a user and an operating system service. Shell provides users with an interface and accepts human-readable commands into the system and executes those commands which can run automatically and give the program’s output in a shell script.

An Operating is made of many components, but its two prime components are –

• Kernel
• Shell

Components of Shell Program

A Kernel is at the nucleus of a computer. It makes the communication between the hardware and software possible. While the Kernel is the innermost part of an operating system, a shell is the outermost one.

A shell in a Linux operating system takes input from you in the form of commands, processes it, and then gives an output. It is the interface through which a user works on the programs, commands, and scripts. A shell is accessed by a terminal which runs it.

When you run the terminal, the Shell issues a command prompt (usually $), where you can type your input, which is then executed when you hit the Enter key. The output or the result is thereafter displayed on the terminal.

The Shell wraps around the delicate interior of an Operating system protecting it from accidental damage. Hence the name Shell.

This Unix/Linux Shell Script tutorial helps understand shell scripting basics to advanced levels.

In this Shell Script tutorial, you will learn-

Click here if the video is not accessible

Types of Shell

There are two main shells in Linux:

1. The Bourne Shell: The prompt for this shell is $ and its derivatives are listed below:

• POSIX shell also is known as sh
• Korn Shell also knew as sh
• Bourne Again SHell also knew as bash (most popular)

2. The C shell: The prompt for this shell is %, and its subcategories are:

• C shell also is known as csh
• Tops C shell also is known as tcsh

We will discuss bash shell based shell scripting in this tutorial.

How to Write Shell Script in Linux/Unix

Shell Scripts are written using text editors. On your Linux system, open a text editor program, open a new file to begin typing a shell script or shell programming, then give the shell permission to execute your shell script and put your script at the location from where the shell can find it.

Let us understand the steps in creating a Shell Script:

1. Create a fileusing a vi editor(or any other editor). Name script file with extension .sh
2. Start the script with #! /bin/sh
3. Write some code.
4. Save the script file as filename.sh
5. For executing the script type bash filename.sh

“#!” is an operator called shebang which directs the script to the interpreter location. So, if we use”#! /bin/sh” the script gets directed to the bourne-shell.

Let’s create a small script –

Let’s see the steps to create Shell Script Programs in Linux/Unix –

Steps to Create Shell Script in Linux/Unix

Command ‘ls’ is executed when we execute the scrip sample.sh file.

Adding shell comments

Commenting is important in any program. In Shell programming, the syntax to add a comment is

Let understand this with an example.

What are Shell Variables?

As discussed earlier, Variables store data in the form of characters and numbers. Similarly, Shell variables are used to store information and they can by the shell only.

For example, the following creates a shell variable and then prints it:

Below is a small script which will use a variable.

Let’s understand, the steps to create and execute the script

As you see, the program picked the value of the variable ‘name’ as Joy and ‘remark’ as excellent.

This is a simple script. You can develop advanced scripts which contain conditional statements, loops, and functions. Shell scripting will make your life easy and Linux administration a breeze.

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What is linux shell scripting pdf

Learn Linux Shell Scripting – Fundamentals of Bash 4.4

This is the code repository for Learn Linux Shell Scripting – Fundamentals of Bash 4.4, published by Packt.

A comprehensive guide to automating administrative tasks with the Bash shell

What is this book about?

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.

This book covers the following exciting features:

• Understand Linux and Bash basics as well as shell scripting fundamentals
• Learn to write simple shell scripts that interact with Linux operating system
• Build, maintain, and deploy scripts in a Linux environment
• Learn best practices for writing shell scripts
• Avoid common pitfalls associated with Bash scripting
• Gain experience and the right toolset to write your own complex shell scripts

If you feel this book is for you, get your copy today!

Instructions and Navigations

All of the code is organized into folders. For example, Chapter02.

The code will look like the following:

Following is what you need for this book: This book targets new and existing Linux system administrators, Windows system administrators or developers who are interested in automating administrative tasks. No prior shell scripting experience is needed but in case you do this book will make a pro quickly. Readers should have a basic understanding of the command line.

We also provide a PDF file that has color images of the screenshots/diagrams used in this book. Click here to download it.

Mastering Linux Shell Scripting — Second Edition [Packt] [Amazon]

Linux Shell Scripting Cookbook — Third Edition [Packt] [Amazon]

Get to Know the Author

Sebastiaan Tammer is a Linux enthusiast from the Netherlands. After attaining his BSc in information sciences, he graduated with an MSc in business informatics, both from Utrecht University. His professional career started in Java development, before he pivoted into a Linux opportunity. Because of this dual background, he feels most at home in a DevOps environment. Besides working extensively with technologies such as Puppet, Chef, Docker, and Kubernetes, he has also attained the RHCE and OSCP certificates. He spends a lot of time in and around Bash. Whether it is creating complex scripting solutions or just automating simple tasks, there is hardly anything he hasn’t done with Bash!

Suggestions and Feedback

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3. A First Script

The first line tells Unix that the file is to be executed by /bin/sh. This is the standard location of the Bourne shell on just about every Unix system. If you’re using GNU/Linux, /bin/sh is normally a symbolic link to bash (or, more recently, dash).

The second line begins with a special symbol: # . This marks the line as a comment, and it is ignored completely by the shell.
The only exception is when the very first line of the file starts with #! — as ours does. This is a special directive which Unix treats specially. It means that even if you are using csh, ksh, or anything else as your interactive shell, that what follows should be interpreted by the Bourne shell.
Similarly, a Perl script may start with the line #!/usr/bin/perl to tell your interactive shell that the program which follows should be executed by perl. For Bourne shell programming, we shall stick to #!/bin/sh.

The third line runs a command: echo , with two parameters, or arguments — the first is «Hello» ; the second is «World» .
Note that echo will automatically put a single space between its parameters.
The # symbol still marks a comment; the # and anything following it is ignored by the shell.

now run chmod 755 first.sh to make the text file executable, and run ./first.sh .
Your screen should then look like this:

You will probably have expected that! You could even just run:

Now let’s make a few changes.
First, note that echo puts ONE space between its parameters. Put a few spaces between «Hello» and «World». What do you expect the output to be? What about putting a TAB character between them?
As always with shell programming, try it and see.
The output is exactly the same! We are calling the echo program with two arguments; it doesn’t care any more than cp does about the gaps in between them. Now modify the code again:

This time it works. You probably expected that, too, if you have experience of other programming languages. But the key to understanding what is going on with more complex command and shell script, is to understand and be able to explain: WHY?
echo has now been called with just ONE argument — the string «Hello World». It prints this out exactly.
The point to understand here is that the shell parses the arguments BEFORE passing them on to the program being called. In this case, it strips the quotes but passes the string as one argument.
As a final example, type in the following script. Try to predict the outcome before you run it:

Is everything as you expected? If not, don’t worry! These are just some of the things we will be covering in this tutorial . and yes, we will be using more powerful commands than echo !

Books and eBooks

My Shell Scripting books, available in Paperback and eBook formats.

Buy this tutorial as a PDF for only $5 $1!

Shell Scripting Tutorial is this tutorial, in 88-page Paperback and eBook formats. Convenient to read on the go, and to keep by your desk as an ever-present companion.

Shell Scripting: Expert Recipes for Linux, Bash and more is my 564-page book on Shell Scripting. The first half explains the features of the shell; the second half has real-world shell scripts, organised by topic, with detailed discussion of each script.

Contact

You can mail me with this form. If you expect a reply, please ensure that the address you specify is valid. Don’t forget to include the simple addition question at the end of the form, to prove that you are a real person!

You can buy the content of this Shell Scripting Tutorial as a PDF!

Источник

Linux Command Line and Shell Scripting Bible

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О книге «Linux Command Line and Shell Scripting Bible»

Talk directly to your system for a faster workflow with automation capability Linux Command Line and Shell Scripting Bible is your essential Linux guide. With detailed instruction and abundant examples, this book teaches you how to bypass the graphical interface and communicate directly with your computer, saving time and expanding capability. This third edition incorporates thirty pages of new functional examples that are fully updated to align with the latest Linux features. Beginning with command line fundamentals, the book moves into shell scripting and shows you the practical application of commands in automating frequently performed functions. This guide includes useful tutorials, and a desk reference value of numerous examples. The Linux command line allows you to type specific shell commands directly into the system to manipulate files and query system resources. Command line statements can be combined into short programs called shell scripts, a practice increasing in popularity due to its usefulness in automation. This book is a complete guide providing detailed instruction and expert advice working within this aspect of Linux. Write simple script utilities to automate tasks Understand the shell, and create shell scripts Produce database, e-mail, and web scripts Study scripting examples ranging from basic to advanced Whether used as a tutorial or as a quick reference, this book contains information that every Linux user should know. Why not learn to use the system to its utmost capability? Linux is a robust system with tremendous potential, and Linux Command Line and Shell Scripting Bible opens the door to new possibilities.

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