> ## Documentation Index
> Fetch the complete documentation index at: https://bunnynet-cb9733c2-support-migration.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Variable Expansion

> Use variable expansion syntax to dynamically configure Edge Rule values based on request parameters.

Variable expansion allows Edge Rules to dynamically configure values based on specific request parameters. Instead of hardcoding URLs or header values, you can use variables that are replaced at runtime with actual request data.

## Supported actions

Variable expansion works with the following Edge Rule actions:

* **Change Origin URL**
* **Redirect to URL**
* **Set Request Header**
* **Set Response Header**

## Syntax

Variables are accessed using the following syntax:

```
%{Collection.Key}
```

Where `Collection` is a group of related variables, and `Key` is the specific value you want to access.

<Note>
  For a complete list of all available variables with examples, see [Dynamic
  Variables](/cdn/edge-rules/dynamic-variables).
</Note>

***

## Variable collections

### RequestHeaders

The `RequestHeaders` collection contains HTTP headers from the incoming request. Headers are automatically mapped based on their name.

| Example                             | Description                             |
| ----------------------------------- | --------------------------------------- |
| `%{RequestHeaders.Host}`            | The `Host` header sent with the request |
| `%{RequestHeaders.User-Agent}`      | The `User-Agent` header                 |
| `%{RequestHeaders.Accept-Language}` | The `Accept-Language` header            |

### Query

The `Query` collection contains URL query parameters. Parameters are automatically mapped based on their key.

For a URL like `?token=abc123&user=42`:

| Example          | Result   |
| ---------------- | -------- |
| `%{Query.token}` | `abc123` |
| `%{Query.user}`  | `42`     |

### Request

The `Request` collection contains information about the HTTP request:

| Key           | Description             | Example                       |
| ------------- | ----------------------- | ----------------------------- |
| `Method`      | The HTTP method         | `GET`, `POST`                 |
| `Path`        | Full URL path and query | `/videos/test.mp4?quality=hd` |
| `QueryString` | Query string only       | `quality=hd`                  |

### Path

The `Path` collection allows you to extract specific segments from the URL path using index-based access.

For the path `/hello/world/bunny/eat/carrot.jpg`:

| Syntax        | Result                       | Description              |
| ------------- | ---------------------------- | ------------------------ |
| `%{Path.0}`   | `hello`                      | Single segment at index  |
| `%{Path.1}`   | `world`                      |                          |
| `%{Path.0-2}` | `hello/world/bunny`          | Range from index 0 to 2  |
| `%{Path.1-3}` | `world/bunny/eat`            | Range from index 1 to 3  |
| `%{Path.3-}`  | `eat/carrot.jpg`             | From index 3 to end      |
| `%{Path.1-}`  | `world/bunny/eat/carrot.jpg` | From index 1 to end      |
| `%{Path.-1}`  | `hello`                      | From start up to index 1 |
| `%{Path.-3}`  | `hello/world/bunny`          | From start up to index 3 |

### Url

The `Url` collection provides parsed components of the request URL:

| Key         | Description                               | Example                 |
| ----------- | ----------------------------------------- | ----------------------- |
| `FileName`  | Filename from the URL (empty for folders) | `video.mp4`             |
| `Path`      | Full URL path and query                   | `/videos/video.mp4?x=1` |
| `Extension` | File extension                            | `mp4`                   |
| `Directory` | Directory path without filename           | `/videos/2024/`         |
| `Hostname`  | Request hostname                          | `cdn.example.com`       |

### User

The `User` collection contains information about the requesting user:

| Key           | Description             | Example          |
| ------------- | ----------------------- | ---------------- |
| `IP`          | End-user IP address     | `203.0.113.10`   |
| `CountryCode` | Two-letter country code | `US`, `DE`, `JP` |

### Server

The `Server` collection contains information about the serving edge server:

| Key        | Description                     | Example          |
| ---------- | ------------------------------- | ---------------- |
| `ZoneCode` | Zone code of the serving server | `NY`, `LA`, `DE` |
| `ID`       | Unique server ID                | `9482`           |

***

## Examples

### Dynamic origin routing

Route requests to different origins based on the first path segment:

**Origin URL:** `https://%{Path.0}.backend.example.com/%{Path.1-}`

For a request to `/api/users/123`, this becomes `https://api.backend.example.com/users/123`.

### Pass query parameter as header

Forward a specific query parameter to your origin as a header:

**Header Name:** `X-Auth-Token`\
**Header Value:** `%{Query.token}`

### Geo-based routing

Add the user's country to the origin request:

**Header Name:** `X-Country`\
**Header Value:** `%{User.CountryCode}`

***

## Related

* [Dynamic Variables](/cdn/edge-rules/dynamic-variables) - Complete variable reference with all examples
* [Rule Ordering](/cdn/edge-rules/ordering) - Control execution order for complex rule sets
* [Middleware Scripts](/scripting/middleware/overview) - For advanced request/response transformations