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

Using the trap command


If a signal or software interrupt is generated while the script is running, then we can define what action is performed by that interrupt handler using the trap command. The trap command helps us in reassigning the system response to a particular signal through the user defined function or commands.

The syntax to use the trap command is either of the following:

$ trap 'command; command' signal-name
$ trap 'command; command' signal-number

The usage as per the preceding syntax is as follows:

trap 'echo "You pressed Control key"; exit 1'  0 1 2 15

This will print the message You pressed Control Key, any SIGINT, SIGHUP, or SIGTERM received by the process:

trap 'rm file.tmp; exit 1'  EXIT INT TERM HUP

When any of the SIGINT, SIGTERM, or SIGHUP signals arrives, then it will delete the file.tmp file and exit with status 1.

While using the trap command, if the command string is surrounded by double quotes, then the command substitution and variable substitution will be done...