Question

For some reason there’s a variable called d that is defined immediately after I enter irb. Any idea what it is?

Answer 1

Are you using irbtools by any chance? If yes, there’s a predefined method called d, that roughly looks like this:

def d
  self.tap { |v| puts v }
end

It can be used to debug message chains like this: obj.some_method.d.other_method.

Since it’s defined at the Object level, it should work if you just call it at the IRB top level where it would return main.