say I've been mucking about in irb and want to save some of/all
previous steps into file.rb, is there a way to do this?

also, I've been going through (mostly reading) some tutorials, and am
just slightly confused on how it works when you call up something, a
class or a method definition, and then recall it later.... it doesn't
overwrite what's previously there, just add to it? though in some
cases it seems to overwrite what's already there... but this clearly
isn't the case if I'm making methods in the Array class, for example.