Switch that takes an argument, which does not begin with '-'.

Methods
P
Instance Public methods
parse(arg, argv, &error)

Returns nil if argument is not present or begins with '-'.

Source: show | on GitHub 

# File lib/optparse.rb, line 528
def parse(arg, argv, &error)
  if !(val = arg) and (argv.empty? or /\A-/ =~ (val = argv[0]))
    return nil, block, nil
  end
  opt = (val = parse_arg(val, &error))[1]
  val = conv_arg(*val)
  if opt and !arg
    argv.shift
  else
    val[0] = nil
  end
  val
end