Main notes taken from the book Mastering Regular Expressions
Info about this book available at http://regex.info
For an online Perl interpreter, https://onecompiler.com/perl can be used
Chapter 1: Introduction to Regular Expressions
Chapter 2: Extended Introductory Examples
Chapter 3: Overview of Regular Expression Features and Flavors
Chapter 4: The Mechanics of Expression Processing
Chapter 5: Practical Regex Techniques
Chapter 6: Crafting an Efficient Expression
Chapter 7: Perl
Chapter 8: Java
Chapter 9: .NET
Chapter 10: PHP