Regular expressions, or just regex, are used in almost all programming languages to define a search pattern that can be used to search for things in a string.

You can learn the basics of regular expressions for free in this complete crash course. It focuses on using regex in JavaScript, but the principles apply in many other programming languages you might choose to use.

This course follows along with the free regular expressions curriculum on freeCodeCamp.org.

You can watch the full video course on the freeCodeCamp.org YouTube channel (45 minute watch).

From https://xkcd.com/208/