Preface

You are likely to be familiar with the "Find and Replace" dialog box from a text editor, word processor, IDE, etc to search for something and replace it with something else. sed is a command line tool that is similar, but much more versatile and feature-rich. Some of the GUI applications may also support regular expressions, a feature which helps to precisely define a matching criteria. You could consider regular expressions as a mini-programming language in itself, designed to solve various text processing needs.

The book heavily leans on examples to present options and features of sed one by one. Regular expressions will also be discussed in detail. However, commands to manipulate data buffers and multiline techniques will be discussed only briefly and some commands are skipped entirely.

It is recommended that you manually type each example and experiment with them. Understanding both the nature of sample input string and the output produced is essential. As an analogy, consider learning to drive a bike or a car — no matter how much you read about them or listen to explanations, you need to practice a lot and infer your own conclusions. Should you feel that copy-paste is ideal for you, code snippets are available chapter wise on GitHub.

Prerequisites

Prior experience working with command line and bash shell, should know concepts like file redirection, command pipeline and so on. Knowing basics of grep will also help in understanding filtering features of sed.

If you are new to the world of command line, check out my curated resources on Linux CLI and Shell scripting before starting this book.

My Command Line Text Processing repository includes a chapter on GNU sed which has been edited and expanded to create this book.

Conventions

  • The examples presented here have been tested on GNU bash shell with GNU sed 4.8 and may include features not available in earlier versions.
  • Code snippets shown are copy pasted from bash shell and modified for presentation purposes. Some commands are preceded by comments to provide context and explanations. Blank lines to improve readability, only real time shown for speed comparisons, output skipped for commands like wget and so on.
  • Unless otherwise noted, all examples and explanations are meant for ASCII characters only.
  • sed would mean GNU sed, grep would mean GNU grep and so on unless otherwise specified.
  • External links are provided for further reading throughout the book. Not necessary to immediately visit them. They have been chosen with care and would help, especially during rereads.
  • The learn_gnused repo has all the code snippets and files used in examples, exercises and other details related to the book. If you are not familiar with git command, click the Code button on the webpage to get the files.

Acknowledgements

Special thanks to all my friends and online acquaintances for their help, support and encouragement, especially during difficult times.

Feedback and Errata

I would highly appreciate if you'd let me know how you felt about this book, it would help to improve this book as well as my future attempts. Also, please do let me know if you spot any error or typo.

Issue Manager: https://github.com/learnbyexample/learn_gnused/issues

E-mail: learnbyexample.net@gmail.com

Twitter: https://twitter.com/learn_byexample

Author info

Sundeep Agarwal is a freelance trainer, author and mentor. His previous experience includes working as a Design Engineer at Analog Devices for more than 5 years. You can find his other works, primarily focused on Linux command line, text processing, scripting languages and curated lists, at https://github.com/learnbyexample. He has also been a technical reviewer for Command Line Fundamentals book and video course published by Packt.

List of books: https://learnbyexample.github.io/books/

License

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

Code snippets are available under MIT License

Resources mentioned in Acknowledgements section above are available under original licenses.

Book version

1.5

See Version_changes.md to track changes across book versions.