How to generate files during build using msbuild

Question

Does anyone know how to modify a csproj file in a way to generate code files during build without actually referencing the files?

A process like :

Answer 1

I wanted to use a bash script to generate code for a project using dotnet core on Linux. Here is what worked for me. And thanks @stukselbax, I built this off of your answer.

Note that the script I'm using to generate the code is called generatecode.sh. Replace this with your own.