on your machine at home/work, you can type into a terminal window / command window:

perlodc Getopt::Long
[download]

to view the documentation in the file. ( I don't run windows, so there may be more to it on those platforms). Or you can browse to metacpan.org, search for the module you're interested in, and read the documentation there. It describes exactly the situation you're asking about.

I suspect you're thinking about interrupt handlers, where you're advised to keep the code short, not call too many other routines, to avoid complications. Nothing like that here, Your program can call A, B, or C, do various work for hours, and never even return to the main. It would be kind of perverted, but you could :-)