gistfile1.rb

# possible solution for ruby-forum.com/topic/203515

$stdin = DATA                       # uses text after __END__ as input

require 'rubygems'                  # fixes load path on some (read: most) systems. read ruby-forum.com/topic/203245 to see why it is evil
require 'active_support/inflector'  # if you have Rails, you have this library. If not: http://gemcutter.org/gems/activesupport


# the base functionality that you wish to give to the classes that implement the commands
module Command

  attr_accessor :params
  
  # in reality, initialize would probably go into your classes that include this module
  # I wasn't able to override this method, not sure why (you can see I was able to override run)
  def initialize( params = Array.new )
    self.params = params
  end  
  
  # code to do whatever you're wanting
  # in this example, just shows a sort of inspection of this object, so you can see more internally what happens
  def run
    "Command:  #{self.class}\n" \
    "Params:   #{params.inspect}"
  end
  
  # if you want, you can register all the commands with something like this
  @registered_commands = Array.new
  
  def self.included( base )
    @registered_commands << base
  end
  
  def self.list
    text_list = @registered_commands.map { |command| "* #{command}\n" }.join
    "The available commands are:\n" \
    "#{text_list.downcase}"
  end

end



# three different command types ( what your other users will create )
class Update
  include Command
end

class Edit
  include Command
end

class Execute
  include Command
  # custom Execute code
  def upcased_params 
    params.map { |param| param.upcase }
  end
  # a custom run method, overrides Command's
  def run
    "Command:          Execute\n" \
    "Modified Params:  #{ upcased_params.inspect }"
  end
end


puts Command.list

puts
puts 'Now Processing The Input:' , '-'*20

# pull them from the command line, turn first word into the command
# create instance of it, pass rest of the commands as arg list, call #run on it

while input = gets
  next if input =~ /^\s*$/                          # skip blank lines
  begin
    puts "Input was: #{input.inspect}"              # display context
    inputs     =  input.split                       # ie 'update user' becomes [ 'update' , 'user' ]
    class_name =  inputs.shift                      # class_name becomes 'update' , inputs becomes [ 'user' ]
    cmd_class  =  class_name.classify.constantize   # cmd_class becomes Update
    cmd        =  cmd_class.new inputs              # cmd becomes instance of Update
    puts cmd.run                                    # execute the run method (which prints out the state of the object)
    puts
  rescue NameError
    puts "#{class_name} is not a valid command"     # if they enter an invalid command
    puts
  end
end

# this is the example input that will get fed into this file ( because of line 1 )
__END__
update user
edit author 12
ecksecute ... was this the command name?
execute I guess it wasn't, lets try this one

edit my paper four me?
create a new universe
execute that thing I stored earlier
edit user1 15
update
etcetera ...