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

Exiting from a loop with a break


In the previous section, we discussed about how continue can be used to exit from the current iteration of a loop. The break command is another way to introduce a new condition within a loop. Unlike continue, however, it causes the loop to be terminated altogether if the condition is met.

In the for_12.sh script, we check the directory's content. If the directory is found, then we are exiting the loop and displaying the message that the first directory is found:

#!/bin/bash
rm -rf sample*
echo > sample_1
echo > sample_2
mkdir sample_3
echo > sample_4

for file in sample*
do
  if [ -d "$file" ]; then
    break;
  fi
done

echo The first directory is $file
rm -rf sample*
exit 0

Let's test the program:

$ chmod +x for_12.sh
$ ./for_12.sh

The following will be the output after executing the preceding commands:

The first directory is sample_3

In the for_13.sh script, we ask the user to enter any number. We print the square of numbers in the while loop. If...