Reference Parameter Value in UserData in AWS Cloudformation

Question

I have this under parameter section ,

Parameters:
  PlatformSelect:
    Description: Cockpit platform Select.
    Type: String
    Default: qa-1
    AllowedValue         


        

Answer 1

What about a combination of Fn::Join and Ref

UserData:
        Fn::Base64:
          Fn::Join:
            - ''
            - - '#!/bin/bash\n'
              - 'print: echo'
              - !Ref 'PlatformSelect' 
              - '>>test.txt\n'

Answer 2

Is there a reason why you are using Mapping in between?

You could easily use !Sub instead

Resources:
  EC2Instance:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: !Ref InstanceType
      KeyName: !Ref KeyName
      Tags:
        - Key: Name
          Value: Test
      UserData:
        Fn::Base64:
          !Sub |
            #!/bin/bash
            ${PlatformSelect}