Book Image

Learning Linux Shell Scripting - Second Edition

By : Ganesh Sanjiv Naik
Book Image

Learning Linux Shell Scripting - Second Edition

By: Ganesh Sanjiv Naik

Overview of this book

Linux is the most powerful and universally adopted OS. 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 reads this file and acts on commands as if they were typed on the keyboard. Learning Linux Shell Scripting covers Bash, GNU Bourne Again Shell, preparing you to work in the exciting world of Linux shell scripting. CentOS is a popular rpm-based stable and secured Linux distribution. Therefore, we have used CentOS distribution instead of Ubuntu distribution. Linux Shell Scripting is independent of Linux distributions, but we have covered both types of distros. We start with an introduction to the Shell environment and basic commands used. Next, we explore process management in Linux OS, real-world essentials such as debugging and perform Shell arithmetic fluently. You'll then take a step ahead and learn new and advanced topics in Shell scripting, such as decision making, starting up a system, and customizing a Linux environment. You will also learn about grep, stream editor, and AWK, which are very powerful text filters and editors. Finally, you'll get to grips with taking backup, using other language scripts in Shell Scripts as well as automating database administration tasks for MySQL and Oracle. By the end of this book, you will be able to confidently use your own shell scripts in the real world.
Table of Contents (17 chapters)

Implementing simple menus with select

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