Book Image

Learning Linux Shell Scripting

By : Ganesh Sanjiv Naik
Book Image

Learning Linux Shell Scripting

By: Ganesh Sanjiv Naik

Overview of this book

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.
Table of Contents (20 chapters)
Learning Linux Shell Scripting
Credits
About the Author
Acknowledgments
About the Reviewers
www.PacktPub.com
Preface
Index

Working in shell


Let's get started by opening the terminal, and we will familiarize ourselves with the Bash Shell environment:

  1. Open the Linux terminal and type in:

    $ echo $SHELL
    /bin/bash
    
  2. The preceding output in terminal says that the current shell is /bin/bash such as BASH shell:

    $ bash --version
    GNU bash, version 2.05.0(1)-release (i386-redhat-linux-gnu)
    Copyright 2000 Free Software Foundation, Inc.
    

Hereafter, we will use the word Shell to signify the BASH shell only. If we intend any other shell, then it will be specifically mentioned by name such as KORN and similar other shells.

In Linux, filenames in lowercase and uppercase are different; for example, the files Hello and hello are two distinct files. This is unlike Windows, where case does not matter.

As far as possible, avoid using spaces in filenames or directory names such as:

  • Wrong file name—Hello World.txt

  • Correct file name—Hello_World.txt or HelloWorld.txt

This will make certain utilities or commands fail or not work as expected, for example, the make utility.

While typing in filenames or directory names of the existing files or folders, use the tab completion feature of Linux. This will make working with Linux faster.