How do I refer to the startup project in visual studio as an external tools argument? -

I want to give the startup project as an argument in an external batch file. Offers drop-down solutions, goals, and projects, but does not offer startup projects.

The solution is not good for me, both target both the project and the changes based on the opening of both the files. I need a single startup project every time.

Is this possible? if so?

Thanks