dos doesn't have start as far as I know.
You are mistaking it for windows

Precisely.

You should probably try integrating DOSBox.exe into your scripts rather than trying to run the scripts inside DOSBox.

Yes, Im sorry, my fault.
But i have another question.

Is it possible to define variables in a batchfile, which are accessible for the programm in the doxbox and a running windows program?

I ask because auf that:
i have a old dos prog, which defines some parameters, after that a .htm file is started and imports of a website are done.

So I need to find out how I can use the defined paramters in dosbox, for firefox in windows - I need a connection between them.

regards

You could pass variables to DOSBox when it starts by including appropriate "set var=value" lines in the autoexec.bat section of the config file.

Passing values back from DOSBox to Windows programs is not something that I think is particularly feasible, unless you could write values to a text file and then reread them. (Don't forget that piping works in DOSBox: you can type "dir > foo.txt" and write the output of "dir" to a text file.)