CLI with sub-commands using dynamic dispatch and a whitelist

metasyntactic_puns.rb

# revision of https://gist.github.com/2583429 with a whitelist

class PunCommands
  PUN_WORDS = %w[foo bar baz]
  
  def self.foo
    puts "you could have fooed me"
  end

  def self.bar
    puts "guy walks into a bar"
  end

  def self.baz
    puts "bazically it works"
  end

  def self.valid_command?(command)
    PUN_WORDS.include?(command.to_s)
  end

  def self.defined_commands
    PUN_WORDS
  end
end

unless ARGV.length == 1
  puts "requires one argument, the command you'd like to run"
  exit 1
end

input_command = ARGV.first.to_sym

if PunCommands.valid_command?(input_command)
  PunCommands.send(input_command)
  exit 0
else
  puts "no command by that name, try: #{PunCommands.defined_commands.join(', ')}"
  exit 1
end