How to configure postcompile commands

I am experimenting with creating a .Net Core Project, which is a NETStandard.Library version 1.6.0.

I wanted to experiment with a post build command, but I noticed now that in our project.json file, there is a "postcompile" script that can be created.

Here is the documentation. https://docs.microsoft.com/en-us/dotnet/articles/core/tools/project-json

I have created a .cmd file, that I am calling from the json file like so:

    "scripts": {     "postcompile": ["copyFiles.cmd"]   }

In my cmd file I can have a simple copy command, which works:

    xcopy /y "C:\Playground\test.txt" "C:\Playground\test\"

What I am stuck on, is what variables are now available to me at this point, to give me access to things like the build output directory?  I can't find a reference to this anywhere.

Thanks in advance.