module POSIX::Spawn

def fd?(object)

the symbolic names :in, :out, or :err.
Returns true if object is an instance of IO, Integer >= 0, or one of the

Determine whether object is fd-like. 
def fd?(object)
  case object
  when Integer
    object >= 0
  when :in, :out, :err, STDIN, STDOUT, STDERR, $stdin, $stdout, $stderr, IO
    true
  else
    object.respond_to?(:to_io) && !object.to_io.nil?
  end
end