Not sure what you are trying to do, but Triggerfish has a handy mkgmap compiler batch file at the bottom of this thread but you’d have to keep all your source in a single directory. If you did that, using Sendmap to create a gmapsupp.IMG should be fairly simple:
What sort of Garmin do you want to send the maps to? USB or serial, and does it have memory card?
If it has a memory card, you can put it in USB mass storage mode, then you just need to copy the IMG file across (which is easily done from a command line).