Automatically, but in a way that, for some reason (typically because
it is too complicated, or too ugly, or perhaps even too trivial), the
speaker doesn't feel like explaining to you. See
magic. “The C-INTERCAL compiler generates C,
then automagically invokes
cc(1)
to produce an executable.”
This term is quite old, going back at least to the mid-70s in jargon
and probably much earlier. The word ‘automagic’ occurred in
advertising (for a shirt-ironing gadget) as far back as the late
1940s.
