Preface

You are likely to be familiar with using a search and replace dialog (usually invoked with the Ctrl+H shortcut) to locate the occurrences of a particular string and replace it with something else. The sed command is a versatile and feature-rich version for search and replace operations, usable from the command line. An important feature that GUI applications may lack is regular expressions, a mini-programming language to precisely define a matching criteria.

This book heavily leans on examples to present features one by one. In addition to command options, 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. Make an effort to understand the sample input as well as the solution presented and check if the output changes (or not!) when you alter some part of the input and the command. As an analogy, consider learning to drive a car — no matter how much you read about them or listen to explanations, you'd need practical experience to become proficient.

Prerequisites

You should be familiar with command line usage in a Unix-like environment. You should also be comfortable with concepts like file redirection and command pipelines. Knowing the basics of the grep command will be handy in understanding the filtering features of sed.

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

Conventions

• The examples presented here have been tested with GNU sed version 4.9 and may include features not available in earlier versions.
• Code snippets are copy pasted from the GNU 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 input.
• sed would mean GNU sed, grep would mean GNU grep and so on unless otherwise specified.
• External links are provided throughout the book for you to explore certain topics in more depth.
• 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 the git command, click the Code button on the webpage to get the files.

Acknowledgements

• GNU sed documentation — manual and examples
• stackoverflow and unix.stackexchange — for getting answers to pertinent questions on sed and related commands
• tex.stackexchange — for help on pandoc and tex related questions
• /r/commandline/, /r/linux4noobs/, /r/linuxquestions/ and /r/linux/ — helpful forums
• canva — cover image
• oxipng, pngquant and svgcleaner — optimizing images
• Warning and Info icons by Amada44 under public domain
• arifmahmudrana for spotting an ambiguous explanation
• mdBook — for web version of the book that you are currently reading
  • mdBook-pagetoc — for adding table of contents for each chapter
  • minify-html — for minifying html files

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 it if you'd let me know how you felt about this book. It could be anything from a simple thank you, pointing out a typo, mistakes in code snippets, which aspects of the book worked for you (or didn't!) and so on. Reader feedback is essential and especially so for self-published authors.

You can reach me via:

• 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 lazy being who prefers to work just enough to support his modest lifestyle. He accumulated vast wealth working as a Design Engineer at Analog Devices and retired from the corporate world at the ripe age of twenty-eight. Unfortunately, he squandered his savings within a few years and had to scramble trying to earn a living. Against all odds, selling programming ebooks saved his lazy self from having to look for a job again. He can now afford all the fantasy ebooks he wants to read and spends unhealthy amount of time browsing the internet.

When the creative muse strikes, he can be found working on yet another programming ebook (which invariably ends up having at least one example with regular expressions). Researching materials for his ebooks and everyday social media usage drowned his bookmarks, so he maintains curated resource lists for sanity sake. He is thankful for free learning resources and open source tools. His own contributions can be found at https://github.com/learnbyexample.

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

2.0

See Version_changes.md to track changes across book versions.