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

Text filtering tools


Normally, Shell scripting involves report generation, which will include processing various text files and filtering their output to finally produce desirable results. Lets start discussing the two Linux commands, namely, more and less:

more: Sometimes we get a very large output on the screen for certain commands, which cannot be viewed completely on one screen. In such cases, we can use the more command to view the output text one page at a time. Add "| more" after the command, as follows:

$ ll /dev | more

The | is called pipe. You will learn more about it in the next chapters. In this command, pressing the spacebar will move the output on the screen one page at a time, or pressing Enter will move the screen by one line at a time.

less: Instead of more, if you use less it will show a screen containing the full text all at once. We can move forward as well as backwards. This is a very useful text filtering tool.

The syntax of usage is as follows:

$ command |  less
e.g...