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)

Piping the output of a loop to a Linux command

If we need to redirect the output of a loop to any other Linux command such as sort, we can even redirect the loop output to be stored in the file:

The following is an example of source code for_14.sh:

#!/bin/bash 
for value in 10 5 27 33 14  25 
do 
      echo  $value 
done | sort -n 

Let's test the program:

    $ chmod +x for_14.sh
    $ ./for_14.sh
  

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

    5
    10
    14
    25
    27
    33
  

In the preceding script, the for loop iterates through a list of numbers that is unsorted. The numbers are printed in the body of the loop, which are enclosed between the do and done commands. Once the loop is complete, the output is piped to the sort command, which, in, turn performs a numerical sort and prints the result on screen.

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