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

Understanding signals and traps


Two types of interrupts exist in the Linux operating system: the hardware interrupt and the software interrupt. Software interrupts are called signals or traps. Software interrupts are used for interprocess synchronizations.

Signals are used to notify about a certain event occurrence or to initiate a certain activity.

We use software signals many times, for example, if any command is not responding after it is typed, then you might have entered Ctrl + C. This sends a SIGINT signal to the process, and the process is terminated. In certain situations, we may want the program to perform a certain activity instead of terminating it using the Ctrl + C command. In such cases, we can use the trap command to ignore a signal or to associate our desired function with that signal.

In operating systems, software interrupts or signals are generated when the process attempts to divide a number by zero or due to power failure, system hang up, illegal instruction execution,...