Normally it would be:
prompt $P$G
press spacebar after G and hit enter

but DOSBox doesn't support the prompt command.

You can try loading DOS command.com, see if FREEDOS has a seperate prompt executable, see if 4DOS has the ability to change the prompt or change the DOSBox code and compile a new binard.

DosFreak wrote:

Normally it would be: prompt $P$G press spacebar after G and hit enter […]
Show full quote

Normally it would be:
prompt $P$G
press spacebar after G and hit enter

but DOSBox doesn't support the prompt command.

I don't think that's what the OP is referring to. "set prompt=$p$g" just displays the path in the command prompt, but DOSBox already does that by default. (Otherwise, there would be a "Z>" prompt instead of a "Z:\>" prompt.)

I believe the OP is simply referring to the space between the DOSBox text and the edge of the DOSBox window.

That is the way I took it, too.

Yes, that's exactly what I meant.

...Now, if DOSBox did support the PROMPT command, then SET PROMPT=$s$p$g would insert a space before the command prompt. But I think you'd at least need to be running 4DOS in order for that to work.

Otherwise, the implementation of this would be ambiguous. You could, say, insert a black border between the edge of the DOSBox window and what DOSBox actually displays, but that border would be there all the time, even when you're playing a game. Would that be acceptable?

I see SDL 2.0 seems to have a quick-and-easy border setting, but even if it was easy to see where that should be thrown into the DOSBox code, DOSBox doesn't really support SDL 2.0 presently.
https://wiki.libsdl.org/SDL_SetWindowBordered

It's not clear from two minutes of Googling as to how you would do this in SDL 1.x, but that would be where to look.
https://wiki.libsdl.org/SDL_SetWindowBordered