Web.Config transforms outside of Microsoft MSBuild?

I created a small function to handle Microsoft's XML Document Transform in PowerShell.

I copied the Microsoft.Web.XmlTransform.dll file from Visual Studio build folder to my script's path, but you can reference it from the source folder if you'd like.

function XmlDocTransform($xml, $xdt)
{
    if (!$xml -or !(Test-Path -path $xml -PathType Leaf)) {
        throw "File not found. $xml";
    }
    if (!$xdt -or !(Test-Path -path $xdt -PathType Leaf)) {
        throw "File not found. $xdt";
    }

    $scriptPath = (Get-Variable MyInvocation -Scope 1).Value.InvocationName | split-path -parent
    Add-Type -LiteralPath "$scriptPath\Microsoft.Web.XmlTransform.dll"

    $xmldoc = New-Object Microsoft.Web.XmlTransform.XmlTransformableDocument;
    $xmldoc.PreserveWhitespace = $true
    $xmldoc.Load($xml);

    $transf = New-Object Microsoft.Web.XmlTransform.XmlTransformation($xdt);
    if ($transf.Apply($xmldoc) -eq $false)
    {
        throw "Transformation failed."
    }
    $xmldoc.Save($xml);
}

To transform web.config using web.release.config:

XmlDocTransform -xml "Web.config" -xdt "Web.Release.config"

Alternatively, you can use Sayed's self-bootstraping Xml Transform script, which will take care of getting the Microsoft.Xml.Xdt.dll for you:

https://gist.github.com/sayedihashimi/f1fdc4bfba74d398ec5b

The logic of the transformation is contained inside of the TransformXml task itself. If you want to call it from code you would have to use the MSBuild API with a mock engine and execute it. I have some code for this if you want.

In your case since you mentioned PowerShell the best thing for you to do is to just create a wrapper MSBuild file to invoke the TransformXml task. I say this because PowerShell is configured to run under .NET 2.0, but the TransformXml task requires .NET 4.0. In order to call it from a dummy MSBuild file you can check my blog at http://sedodream.com/2010/04/26/ConfigTransformationsOutsideOfWebAppBuilds.aspx, but I've also pasted a sample from that link below.

<Project ToolsVersion="4.0" DefaultTargets="Demo" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <UsingTask TaskName="TransformXml"
             AssemblyFile="$(MSBuildExtensionsPath)\Microsoft\VisualStudio\v10.0\Web\Microsoft.Web.Publishing.Tasks.dll"/>

    <Target Name="Demo">
        <TransformXml Source="app.config"
                      Transform="Transform.xml"
                      Destination="app.prod.config"/>
    </Target>
</Project>

For mono, this should work (tested on mono 6.4, macos, 2019) :

<Project DefaultTargets="TransformConfig" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <UsingTask TaskName="TransformXml"
    AssemblyFile="$(MSBuildSDKsPath)/Microsoft.NET.Sdk.Publish/tools/net46/Microsoft.NET.Sdk.Publish.Tasks.dll"/>
  <PropertyGroup>
    <TransformSource>Web.config</TransformSource>
    <Transformer>Web.Live.config</Transformer>
    <Destination>Output.Web.config</Destination>
  </PropertyGroup>
  <Target Name="TransformConfig">
    <Message Text="From TransformSource : $(TransformSource)" />
    <Message Text="Using Transform : $(Transformer)" />
    <Message Text="Output : $(Destination)" />
    <Message Text="MSBuildSDKsPath=$(MSBuildSDKsPath)" Condition="'$(MSBuildSDKsPath)' != ''" />
    <TransformXml Source="$(TransformSource)" Transform="$(Transformer)" Destination="$(Destination)"/>
  </Target>
</Project>

which you can run with just msbuild or supply parameters with

msbuild /p:TransformSource=... /p:Transformer=...

Based on Michel's answer I wrote a C# function that will accomplish the same.

Of course you could invoke the resultant DLL with PowerShell, but I was actually looking for a fully programatic version, so here it is, in case anybody else is looking for similar solution:

using Microsoft.Web.XmlTransform;

...

public static void TransformConfig(string configFileName, string transformFileName)
{
     var document = new XmlTransformableDocument();
     document.PreserveWhitespace = true;
     document.Load(configFileName);

     var transformation = new XmlTransformation(transformFileName);
     if (!transformation.Apply(document))
     {
         throw new Exception("Transformation Failed");
     }
     document.Save(configFileName);
}

You will just need to include reference to following:

C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v11.0\Web\Microsoft.Web.XmlTransform.dll