> For the complete documentation index, see [llms.txt](https://docs.scanner.dev/scanner/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.scanner.dev/scanner/using-scanner-complete-feature-reference/beta-features/scalar-functions-and-operators/regex.extract.md).

# regex.extract()

`regex.extract(haystack, pattern [, group])` extracts a substring matching a regex pattern from a string.

## Returns

* if `haystack` is a string and `pattern` matches, returns the matched substring (or the specified capture group if `group` is provided).
  * `group` 0 returns the entire match (default).
  * `group` 1 returns the first capture group `(...)`.
  * `group` 2 returns the second capture group, etc.
* if no match is found or inputs are invalid, returns `null`.

## Examples

```javascript
// extract the first IPv4 address from a message
regex.extract(message, /\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/)

// extract domain from email
regex.extract(email, /@(.+)$/, 1)

// extract capture groups
| eval address = "123 Sesame Street",
  street_number = regex.extract(address, /^(\d+)\s+(.+)$/, 1), // 123
  street_name   = regex.extract(address, /^(\d+)\s+(.+)$/, 2)  // Sesame Street
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.scanner.dev/scanner/using-scanner-complete-feature-reference/beta-features/scalar-functions-and-operators/regex.extract.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.