Introducing Regular Expressions
By Michael Fitzgerald

If you're new to regular expressions, this book is a good place to start. It has a complete guide, step-by-step, full of examples.

Regular Expressions Cookbook, 2nd Edition
By Jan Goyvaerts and Steven Levithan

This book has more than 140 practical examples. It provides everything you need to solve a wide range of real-world problems. It also talks about flavors of the most used programming languages like C#, Java, JavaScript, Perl, PHP, Python, Ruby, and VB.NET.

RegexOne
Link: https://regexone.com/

This website provides a Regular Expression tutorial for beginners, step-by-step, with practical exercises.

Regex 101
Link: https://regex101.com/

This website offers a platform for creating and practicing regular expressions.