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)

Running loops in the background

In certain situations, the script with loops may take a lot of time to complete. In such situations, we may decide to run the script containing loops in the background so that we can continue other activities in the same terminals. The advantage of this will be that the Terminal will be free to give the next commands.

The following for_15.sh script is the technique to run a script with loops in
the background:

#!/bin/bash 
for animal in Tiger Lion Cat Dog 
do 
     echo $animal 
    sleep 1 
done & 

Let's test the program:

    $ chmod +x for_15.sh
    $ ./for_15.sh
  

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

    Tiger
    Lion
    Cat
    Dog
  

In the preceding script, the for loop will process the animals Tiger, Lion, Cat, and Dog sequentially. The variable animal will be assigned the animal names one after...