Book Image

Mastering Linux Shell Scripting

By : Andrew Mallett
Book Image

Mastering Linux Shell Scripting

By: Andrew Mallett

Overview of this book

Shell scripting is a quick method to prototype a complex application or a problem by automating tasks when working on Linux-based systems. Using both simple one-line commands and command sequences complex problems can be solved with ease, from text processing to backing up sysadmin tools. In this book, you’ll discover everything you need to know to master shell scripting and make informed choices about the elements you employ. Get to grips with the fundamentals of creating and running a script in normal mode, and in debug mode. Learn about various conditional statements' code snippets, and realize the power of repetition and loops in your shell script. Implement functions and edit files using the Stream Editor, script in Perl, program in Python – as well as complete coverage of other scripting languages to ensure you can choose the best tool for your project.
Table of Contents (21 chapters)
Mastering Linux Shell Scripting
About the Author
About the Reviewer

Chapter 8. Introducing sed

In the previous chapter, we saw that we could make use of sed to edit files from within our scripts. The sed command is the Stream Editor and opens the file line by line to search or edit the file contents. Historically, this goes way back to Unix where systems may not have had enough RAM to open very large files. Using sed was absolutely required to carry out edits. Even today, we will use sed to make changes and display data from files with hundreds and thousands of entries. It is simpler and easier and more reliable than a human trying to do the same thing. Most importantly, as we have seen, we can use sed in scripts to edit the files automatically, no human interaction is required.

We will start by looking at grep and search the files for text. The re in grep command is short for Regular Expression. This introduces the power of POSIX Compliant Regular Expressions before we look at sed. Even though we are not looking at scripting in this chapter, we will be...