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 traps in function


If we use the trap command inside a function in script, then the reassigned signal behavior will become global inside a script. We can check this effect in the following script example.

Let's write Shell script trap_01.sh as follows:

#!/bin/bash
trap "echo  caught signal SIGINT" SIGINT
trap "echo  caught signal SIGQUIT" 3
trap "echo  caught signal SIGTERM" 15
while :
do
    sleep 50
done

Let's test the program as follows:

$ chmod +x trap_01.sh
$ ./ trap_01.sh

Output:

^Ccaught signal SIGINT
^\Quit (core dumped)
caught signal SIGQUIT

Let's write one more Shell script trap_02.sh as follows:

#!/bin/bash

trap "echo  caught signal SIGINT" SIGINT
trap "echo  caught signal SIGQUIT" 3
trap "echo  caught signal SIGTERM" 15
trap "echo caught signal SIGTSTP" TSTP

echo "Enter any string (type 'dough' to exit)."
while true
do
    echo "Rolling...\c"
    read string
    if [ "$string" = "dough" ]
    then
        break
    fi
done
echo "Exiting normally"

Let's test the program as follows...