Found a buddy who used something like:

hostname = open("|hostname").gets

And...

I see that it works, but I don't find any of the documentation that makes sense.

So -- it seems to be IO class, but how?  There's no IO declaration there.
Also, I can't find anything that says you can open a command with a preceding 
pipe and get the output of the executed command.

I'm familiar with perls open: open(FH, "hostname |") with a suffixed pipe -- 
which is consistent with unix pipe usage.

But can someone explain to me what's going on here so my brain doesn't implode?