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

Implementing simple menus with select


With the Bash shell, it is possible to create simple menus with the help of the select built-in command.

The syntax of select is as follows:

            PS3=prompting-text
            select VARIABLE in item1 item2 item3
            do
              commands
            done

The advantage of a menu with select is that we can have an endless loop with it. We can have a condition in which we exit the loop.

In the following script select_01.sh, we show the menu with five options such as a, bc, def, ghi, and jkl. The script will execute the command inside do and done:

#!/bin/bash
select var1 in a  bc   def    ghi   jkl
do
echo "Present value of var1 is $var1
done

Let's test the program:

$ chmod +x select_01.sh
$ ./select_01.sh

The following will be the output after executing the preceding commands:

1) a
2) bc
3) def
4) ghi
5) jkl
#? 2
"Present value of var1 is bc
#? 4
"Present value of var1 is ghi
#? 5
"Present value of var1 is jkl
#?
Press     ^C    to quit

We...