# Regular Expression

> An overview of Regular Expressions (a way to search for patterns in text in a programming language) from my perspective and experience.

Source: https://curiouslychase.com/posts/regular-expression/

**Regular Expressions are a super power.**

Regular expressions [^1] are a way for someone to give a programming language a pattern to search for in text.

As a programmer I find myself using them fairly frequently.

As a simple example (using [JavaScript](https://curiouslychase.com/posts/javascript/)), let's say I've built an application that allows someone to input a Slack channel URL and I want to get the Slack workspace and channel ID from the URL.

A Slack channel URL is made up of:
- a protocol (https)
- a Slack workspace (something.slack.com)
- "archives"
- a channel

An example URL might look like:
```
https://curious.slack.com/archives/C019PPFA2BV
```

I want to extract "curious" and "C019PPFA2BV" (and be able to do it regardless of what the values are).

**This is where regular expressions shine.**

A regular expression to match this _pattern_ would look like this:

```
^https:\/\/([\w\d\-_]+)\.slack\.com\/archives\/([\d\w]+)$
```

I won't get into the pattern itself, but you can see that it looks _similar_ to the URL pattern we want to match (you can see "slack.com" and "archives").

There are also two sets of parenthesis `()`. These are called capture groups. A capture group _captures_ whatever content matches that part of the regular expression and returns it as a group.

This regular expression, based on the URL, will find _one_ **Match** and _two_ **Groups**:

- **Match** is the whole URL because it matches the whole regular expression
- **Group 1** is "curious" because it matched the first regular expression subset.
- **Group 2** is "C019PPFA2BV" because it matched the second regular expression subset.

As you can imagine, this means you could build an application with _infinite_ permutations and always have one way to define the pattern you're looking for and any values you want to extract from the permutation.

# Helpful Links
- [Regex 101](https://regex101.com/) is an excellent tool for writing a regular expression and testing the expression against a string.

[^1]: Also called "RegEx"