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Fn::Transform

The intrinsic function `Fn::Transform` specifies a macro to perform custom processing on part of a stack template. Macros enable you to perform custom processing on templates, from simple actions like find-and-replace operations to extensive transformations of entire templates. For more information, see Using AWS CloudFormation macros to perform custom processing on templates.

Using AWS CloudFormation macros to perform custom processing on templates

You can also use `Fn::Transform` to call the `AWS::Include transform` transform, which is a macro hosted by AWS CloudFormation.

Declaration

JSON

Syntax for the full function name:

{
    "Fn::Transform": {
        "Name": "macro name",
        "Parameters": {
            "Key": "value"
        }
    }
}

Syntax for the short form:

{
    "Transform": {
        "Name": "macro name",
        "Parameters": {
            "Key": "value"
        }
    }
}

YAML

Syntax for the full function name:

Fn::Transform:
  Name : macro name
  Parameters :
          Key : value

Syntax for the short form:

Transform:
  Name: macro name
  Parameters:
    Key: value

Parameters

Name

The name of the macro you want to perform the processing.

Parameters

The list parameters, specified as key-value pairs, to pass to the macro.

Return value

The processed template snippet to be included in the processed stack template.

Examples

The following example calls the `AWS::Include` transform, specifying that the location to retrieve a template snippet from is passed in the `InputValue` parameter.

JSON

1. {
2.    "Fn::Transform" : {
3.        "Name" : "AWS::Include",
4.        "Parameters" : {
5.            "Location" : { "Ref" : "InputValue" }
6.         }
7.     }
8. }

YAML

1. 'Fn::Transform':
2.     Name: 'AWS::Include'
3.     Parameters: {Location: {Ref: InputValue}}

The following example calls the `AWS::Include` transform, specifying that the location to retrieve a template snippet from is located in the `RegionMap` mapping, under the key `us-east-1` and nested key `s3Location`.

JSON

1. {
2.    "Fn::Transform" : {
3.        "Name" : "AWS::Include",
4.        "Parameters" : {
5.            "Location" : {"Fn::FindInMap" : ["RegionMap", "us-east-1", "s3Location"] }
6.         }
7.     }
8. }

YAML

1. 'Fn::Transform':
2.     Name: 'AWS::Include'
3.     Parameters: {Location: {'Fn::FindInMap': [RegionMap, us-east-1, s3Location]}}

Supported functions

None. AWS CloudFormation passes any intrinsic function calls included in `Fn::Transform` to the specified macro as literal strings. For more information, see AWS CloudFormation macro function interface.

AWS CloudFormation macro function interface