RegEx

Introduction

This article contains notes for RegEx respectively Regular Expressions and also some useful ressources.

RegEx are not Regular Expressions in the narrower sense of the word but today both tearms are used more or less interchangably. More on that: https://www.rexegg.com/regex-vs-regular-expression.html

General Rules

Meta Characters

Meta Character	Example
Single Character	.
Character class digit	\d
Character class character	\w
Character class whitespace (Space, tab, new line, carriage return)	\s
Inversion of character classes (Not)	\D, \W, \S
Word and text boundaries	b ^ $

Ranges

Range	Example
Character class range	[a-c]
Inversion of character class range	[^abc]

Quantifiers

Quantifier	Example
Zero or one character	?
Zero or more characters (Kleene Star)	*
One or more characters (Kleene Plus)	+
Three characters	{3}
Four to 20 characters	{4,20}

White Space Characters

White Space	Example
Space	_
Tab	\t
New line	\n
Carriage return	\r
Any white space character	\s

Line start and end

Type	Example
Start of line	^
End of line	$

Groups and nested groups

Type	String	Expression	Results
Group Example 1	IMG1000.png	^(IMG\d+\.png)$	IMG1000.png
Group Example 2	IMG1000.png	^(IMG\d+)\.png$	IMG1000
Nested group	IMG1000.png	^(IMG(\d+))\.png$	Group 1: IMG1000 Group 2: 1000
Multiple groups	1920x1080	(\d+)x(\d+)	Group 1: IMG1000 Group 2: 1000
Grouping with alternatives	Monday or Tuesday	(Mon|Tues)day	Match 1: Monday Group 1: Mon Match 2: Tuesday Group 2: Tues

Online Regex Tools

• Interpreter
  • https://regexr.com/
  • https://regex101.com/
• Visualization
  • https://regexper.com/

Tutorials and Guides

Guide (german): https://t3n.de/news/regex-guide-t3n-552858/

Quick Start Cheat Sheet: https://www.rexegg.com/regex-quickstart.html

Advanced tutorial: https://www.rexegg.com/regex-disambiguation.html

Practical tutorial: https://regexone.com/

Regex with JavaScript: https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/#regular-expressions