What is the meaning of $$ in Ruby?

Question

irb(main):002:0> $$
=> 5052

What is the meaning of $$ in Ruby and How/Where to use it?

Answer 1

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

This example shows how the process ID can be used. Process ID is part of 'Execution Environment Variables' (part of predifined variables).