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

The basics of regular expressions


A sequence of characters that have certain patterns of text (with meta-characters), which will be searched from in a larger text or file is called regular expressions:

$ ll /proc | grep cpuinfo

In the preceding command, the grep utility will search for the cpuinfo text in all lines of input text and will print lines that have the cpuinfo text.

The utilities such as grep, sed, or awk use regular expressions for filtering text and then apply various processing commands as required by the user. The lines which do not match the pattern will be rejected. The following diagram explains the same concept:

In Chapter 3, Using Test Processing and Filters in Your Scripts, you learned about the basics of regular expressions and pattern matching using the vi editor and the grep utility.