In MSX-DOS2 you have a nifty environment string called PROGRAM where the program being executed from COMMAND2.COM is located in full pathspec.

I'd like to set up something similar for MSX-DOS1. Using openMSX I found a couple of addresses where the location of the program being executed from COMMAND.COM but the problem is these addresses may differ with 1 or 2 drives (also boot with CTRL pressed) and multiple disk interfaces.

Is there are way to get this info in a trustful manner? And if so, how?