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

Looping with the for command


For iterative operations, the bash shell uses three types of loops: for, while, and until. Using the for looping command, we can execute a set of commands for a finite number of times for every item in a list. In the for loop command, the user-defined variable is specified. After the in command, the keyword list of values can be specified. The user-defined variable will get the value from that list and all statements between do and done get executed until it reaches the end of the list.

The purpose of the for loop is to process a list of elements. It has the following syntax:

for variable in element1 element2 element3
do
commands
done

The simple script with the for loop could be as follows:

for command in clear date cal
do
  sleep 1
  $command
Done

In the preceding script, the commands clear, date, and cal will be called one after another. The sleep command will be called before every command for a second.

If we need to loop continuously or infinitely, then the following...