get

# File lib/getoptlong.rb, line 424
  def get
    option_name, option_argument = nil, ''

    #
    # Check status.
    #
    return nil if @error != nil
    case @status
    when STATUS_YET
      @status = STATUS_STARTED
    when STATUS_TERMINATED
      return nil
    end

    #
    # Get next option argument.
    #
    if 0 < @rest_singles.length
      argument = '-' + @rest_singles
    elsif (ARGV.length == 0)
      terminate
      return nil
    elsif @ordering == PERMUTE
      while 0 < ARGV.length && ARGV[0] !~ /^-./
        @non_option_arguments.push(ARGV.shift)
      end
      if ARGV.length == 0
        terminate
        return nil
      end
      argument = ARGV.shift
    elsif @ordering == REQUIRE_ORDER 
      if (ARGV[0] !~ /^-./)
        terminate
        return nil
      end
      argument = ARGV.shift
    else
      argument = ARGV.shift
    end

    #
    # Check the special argument `--'.
    # `--' indicates the end of the option list.
    #
    if argument == '--' && @rest_singles.length == 0
      terminate
      return nil
    end

    #
    # Check for long and short options.
    #
    if argument =~ /^(--[^=]+)/ && @rest_singles.length == 0
      #
      # This is a long style option, which start with `--'.
      #
      pattern = $1
      if @canonical_names.include?(pattern)
        option_name = pattern
      else
        #
        # The option `option_name' is not registered in `@canonical_names'.
        # It may be an abbreviated.
        #
        matches = []
        @canonical_names.each_key do |key|
          if key.index(pattern) == 0
            option_name = key
            matches << key
          end
        end
        if 2 <= matches.length
          set_error(AmbiguousOption, "option `#{argument}' is ambiguous between #{matches.join(', ')}")
        elsif matches.length == 0
          set_error(InvalidOption, "unrecognized option `#{argument}'")
        end
      end

      #
      # Check an argument to the option.
      #
      if @argument_flags[option_name] == REQUIRED_ARGUMENT
        if argument =~ /=(.*)$/
          option_argument = $1
        elsif 0 < ARGV.length
          option_argument = ARGV.shift
        else
          set_error(MissingArgument,
                    "option `#{argument}' requires an argument")
        end
      elsif @argument_flags[option_name] == OPTIONAL_ARGUMENT
        if argument =~ /=(.*)$/
          option_argument = $1
        elsif 0 < ARGV.length && ARGV[0] !~ /^-./
          option_argument = ARGV.shift
        else
          option_argument = ''
        end
      elsif argument =~ /=(.*)$/
        set_error(NeedlessArgument,
                  "option `#{option_name}' doesn't allow an argument")
      end

    elsif argument =~ /^(-(.))(.*)/
      #
      # This is a short style option, which start with `-' (not `--').
      # Short options may be catenated (e.g. `-l -g' is equivalent to
      # `-lg').
      #
      option_name, ch, @rest_singles = $1, $2, $3

      if @canonical_names.include?(option_name)
        #
        # The option `option_name' is found in `@canonical_names'.
        # Check its argument.
        #
        if @argument_flags[option_name] == REQUIRED_ARGUMENT
          if 0 < @rest_singles.length
            option_argument = @rest_singles
            @rest_singles = ''
          elsif 0 < ARGV.length
            option_argument = ARGV.shift
          else
            # 1003.2 specifies the format of this message.
            set_error(MissingArgument, "option requires an argument -- #{ch}")
          end
        elsif @argument_flags[option_name] == OPTIONAL_ARGUMENT
          if 0 < @rest_singles.length
            option_argument = @rest_singles
            @rest_singles = ''
          elsif 0 < ARGV.length && ARGV[0] !~ /^-./
            option_argument = ARGV.shift
          else
            option_argument = ''
          end
        end
      else
        #
        # This is an invalid option.
        # 1003.2 specifies the format of this message.
        #
        if ENV.include?('POSIXLY_CORRECT')
          set_error(InvalidOption, "invalid option -- #{ch}")
        else
          set_error(InvalidOption, "invalid option -- #{ch}")
        end
      end
    else
      #
      # This is a non-option argument.
      # Only RETURN_IN_ORDER falled into here.
      #
      return '', argument
    end

    return @canonical_names[option_name], option_argument
  end