CODEWITHSUNDEEP
aws-cloudformation
mana
mana

Reputation: 6547

How to escape "${}" in cloudformations "Fn::Sub"

I want this resource to work with the !Sub (or Fn::Sub) intrinsic function

Resource: !Sub 'arn:aws:iam::${AWS::AccountId}:user/${aws:username}'

The aws:username is a policy variable that mustn't be replaced.

One solution would be to use Fn::Join instead and write a bit more boilerplate code.

Better: Can you escape the ${aws:username} so that !Sub will work here? Unfortunately, the documentation does not mention anything about escaping.

Upvotes: 52

Views: 22562

Answers (1)

jens walter
jens walter

Reputation: 14029

You actually can escape $ characters with ${!}.

So your resource would look like this:

Resource: !Sub 'arn:aws:iam::${AWS::AccountId}:user/${!aws:username}'

It is mentioned in the docs under the string parameter section.

To write a dollar sign and curly braces (${}) literally, add an exclamation point (!) after the open curly brace, such as ${!Literal}. AWS CloudFormation resolves this text as ${Literal}.

Upvotes: 98

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