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

Switching case


Apart from simple branches with if, it is also possible to process multiple decision-making operations using the case command. In a case statement, the expression contained in a variable is compared with a number of expressions, and for each expression matched, a command is executed.

It is possible to have multiple branching using the if/elif/else commands. But if more than two or three elif commands are used, then code becomes very complex. When all the different conditions are depending on a single variable, in such cases, the esac statement is used. The interpreter checks the value of the case variable against value1, value2, value3, and so on, till the match is found. If the value is matched then all the statements after that case value are executed till the double semicolon is reached. If nothing is matched then statements after esac are executed. Wildcard characters and pipe (vertical bar for ORing two values) are allowed in the case statement.

A case statement has the...