    # File lib/plugins/command_plus.rb, line 12
        def alias_command(arg)
          original, new = arg.split(/\s+/)
          if @commands[original.to_sym]
            @commands[new.to_sym] = @commands[original.to_sym].clone
            @commands[new.to_sym].name    = new.to_sym
            @commands[new.to_sym].aliases = []
            @commands[new.to_sym].help    = ''
            puts "alias '#{original}' to '#{new}'."
          else
            raise "#{original} command is not found."
          end
        end