---
_db_id: 177
content_type: topic
ready: true
title: Regular Expression Resources
---

A regular expression, regex or regexp (sometimes called a rational expression) is a sequence of characters that define a search pattern. Usually such patterns are used by string searching algorithms for "find" or "find and replace" operations on strings, or for input validation.
-- [wikipedia](https://en.wikipedia.org/wiki/Regular_expression)

Regular expressions are very useful. We use them to:

- validate user input
- url matching: If you are working with any kind of web backend technology you will come across this
- extracting and cleaning data
  And many many other things

It's not worth memorizing this stuff, but you should understand it.

## General Regular Expressions

- Video: [Best of Fluent 2012: /Reg(exp){2}lained/: Demystifying Regular Expressions](https://www.youtube.com/watch?v=EkluES9Rvak)

## Python Regular expressions

- https://www.w3schools.com/python/python_regex.asp - Introduction to Regular Expression.
- https://docs.python.org/3/library/re.html - Python has a built-in package called re, which can be used to work with Regular Expressions.

## Javascript Regular Expressions

- https://www.w3schools.com/js/js_regexp.asp

## Java Regular Expressions

- https://www.javatpoint.com/java-regex