This is a Ruby tree! It shows every object from the Ruby Programming Language in a tree format.

pid 

        # IO.pid

(from ruby core)
---
    pid -> integer or nil

---

Returns the process ID of a child process associated with the stream,
which will have been set by IO#popen, or `nil` if the stream was not
created by IO#popen:

    pipe = IO.popen("-")
    if pipe
      $stderr.puts "In parent, child pid is #{pipe.pid}"
    else
      $stderr.puts "In child, pid is #{$$}"
    end

Output:

    In child, pid is 26209
    In parent, child pid is 26209

This is MURDOC! A Ruby documentation browser inspired by Smalltalk-80. It allows you to learn about Ruby by browsing through its class hierarchies, and see any of its methods.