Book Image

Linux Shell Scripting Bootcamp

By : James K Lewis
Book Image

Linux Shell Scripting Bootcamp

By: James K Lewis

Overview of this book

Linux Shell Scripting Bootcamp is all about learning the essentials of script creation, validating parameters, and checking for the existence of files and other items needed by the script. We will use scripts to explore iterative operations using loops and learn different types of loop statements, with their differences. Along with this, we will also create a numbered backup script for backup files. Further, you will get well-versed with how variables work on a Linux system and how they relate to scripts. You’ll also learn how to create and call subroutines in a script and create interactive scripts. The most important archive commands, zip and tar, are also discussed for performing backups. Later, you will dive deeper by understanding the use of wget and curl scripts and the use of checksum and file encryption in further chapters. Finally, you will learn how to debug scripts and scripting best practices that will enable you to write a great code every time! By the end of the book, you will be able to write shell scripts that can dig data from the web and process it efficiently.
Table of Contents (19 chapters)
Linux Shell Scripting Bootcamp
Credits
About the Author
Acknowledgement
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface
Index

Command piping


Now let's look at command piping, which is the ability to run a command and have the output from it serve as the input to another command.

Suppose a program or script named loop1 is running on your system and you want to know the PID of it. You could run the ps auxw command to a file, and then grep the file for loop1. Alternatively, you could do it in one step by using a pipe as follows:

Pretty cool, right? This is a very powerful feature in a Linux system and is used extensively. We will be seeing a lot more of this soon.

The next section shows another very short script using some command piping. This clears the screen and then shows only the first 10 lines from dmesg:

Chapter 4 - Script 2

#!/bin/sh
#
# 5/8/2017
#
tput clear
dmesg | head

And here is the output:

The next section shows file redirection.

Chapter 4 - Script 3

#!/bin/sh
#
# 5/8/2017
#
FN=/tmp/dmesg.txt
dmesg > $FN
echo "File $FN created."
exit 0

Try it on your system.

This shows how easy it is to create a script to perform...