# API Gateway stage variables reference for REST APIs in API Gateway
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 You can use API Gateway stage variables in the following cases.

## Parameter mapping expressions
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A stage variable can be used in a parameter mapping expression for an API method's request or response header parameter, without any partial substitution. In the following example, the stage variable is referenced without the `$` and the enclosing `{...}`. 
+ `stageVariables.<variable_name>`

## Mapping templates
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 A stage variable can be used anywhere in a mapping template, as shown in the following examples. 
+  `{ "name" : "$stageVariables.<variable_name>"}`
+ `{ "name" : "${stageVariables.<variable_name>}"}`

## HTTP integration URIs
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A stage variable can be used as part of an HTTP integration URL, as shown in the following examples:
+ A full URI without protocol – `http://${stageVariables.<variable_name>}`
+ A full domain – `http://${stageVariables.<variable_name>}/resource/operation`
+ A subdomain – `http://${stageVariables.<variable_name>}.example.com/resource/operation`
+ A path – `http://example.com/${stageVariables.<variable_name>}/bar`
+ A query string – `http://example.com/foo?q=${stageVariables.<variable_name>}` 

## Amazon integration URIs
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 A stage variable can be used as part of Amazon URI action or path components, as shown in the following example.
+ `arn:aws:apigateway:<region>:<service>:${stageVariables.<variable_name>}`

## Amazon integration URIs (Lambda functions)
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 A stage variable can be used in place of a Lambda function name, or version/alias, as shown in the following examples. 
+ `arn:aws:apigateway:<region>:lambda:path/2015-03-31/functions/arn:aws:lambda:<region>:<account_id>:function:${stageVariables.<function_variable_name>}/invocations`
+ `arn:aws:apigateway:<region>:lambda:path/2015-03-31/functions/arn:aws:lambda:<region>:<account_id>:function:<function_name>:${stageVariables.<version_variable_name>}/invocations`

**Note**  
To use a stage variable for a Lambda function, the function must be in the same account as the API. Stage variables don't support cross-account Lambda functions.

## Amazon Cognito user pool
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A stage variable can be used in place of a Amazon Cognito user pool for a `COGNITO_USER_POOLS` authorizer.
+ `arn:aws:cognito-idp:<region>:<account_id>:userpool/${stageVariables.<variable_name>}`

## Amazon integration credentials
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 A stage variable can be used as part of Amazon user/role credential ARN, as shown in the following example. 
+  `arn:aws:iam::<account_id>:${stageVariables.<variable_name>}`