Public/Intrinsic Functions/Add-FnSub.ps1
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function Add-FnSub { <# .SYNOPSIS Adds the intrinsic function "Fn::Sub" to a resource property .DESCRIPTION The intrinsic function Fn::Sub substitutes variables in an input string with values that you specify. In your templates, you can use this function to construct commands or outputs that include values that aren't available until you create or update a stack. ** Important ** As Fn::Sub uses ${Var} syntax, it's important to remember to escape the $ at the head of the subbed variable when calling the function, otherwise Powershell will attempt to convert the variable into a value when adding it to the object and break the CloudFormation function's intended use. Please see the example below for reference. .LINK http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-sub.html .PARAMETER String Input string with the Variable names surrounded in braces, i.e. "/opt/aws/bin/cfn-init -v --stack ${AWS::StackName} --resource LaunchConfig --configsets wordpress_install --region ${AWS::Region}" You MUST escape the dollar sign before each variable brace when using this module, otherwise Powershell will attempt to convert it to a variable and not take it as a literal string. .PARAMETER Mapping A hashtable containing mappings, with the key being the variable name and the value being what you would like to substitute for the variable. The value can be another function. .EXAMPLE Add-FnSub -String "www.`${Domain}" -Mapping @{Domain = (Add-FnRef -Ref "RootDomainName")} When the template is exported, this will convert to: {"Fn::Sub":["www.${Domain}",{"Domain":{"Ref":"RootDomainName"}}]} .NOTES You can use the following functions in the Fn::Sub function: Fn::Base64 Fn::FindInMap Fn::GetAtt Fn::GetAZs Fn::If Fn::Join Fn::Select Ref .FUNCTIONALITY Vaporshell #> [OutputType('Vaporshell.Function.Sub')] [cmdletbinding()] Param ( [parameter(Mandatory = $true,Position = 0)] [System.String] $String, [parameter(Mandatory = $false,Position = 1)] [System.Collections.Hashtable] $Mapping ) if ($Mapping) { $obj = [PSCustomObject][Ordered]@{ "Fn::Sub" = @($String,$Mapping) } } else { $obj = [PSCustomObject][Ordered]@{ "Fn::Sub" = $String } } $obj | Add-ObjectDetail -TypeName 'Vaporshell.Function','Vaporshell.Function.Sub' Write-Verbose "Resulting JSON from $($MyInvocation.MyCommand): `n`n`t$($obj | ConvertTo-Json -Depth 5 -Compress)`n" } |