Ruby on Railsで定数の指定 ref: http://qiita.com/srockstyle/items/daed31a78c343e607822

file0.txt

ApplicationCotnroller < ActionController::Base
    NUM = 1
    ...
end

file1.txt

BookController < ApplicationController  
    def read   
        ## ここに定数いれる
        @number = NUM
    end
end

file2.txt

module Constants
    ## Constants::NUMでアクセスできる
    NUM = 1
end

## こっちはTITLEでアクセスできる
TITLE = 'Story Of The Ring'

file3.txt

if Rails.env == "production"
    ## 本番の定数
else
    ## 開発の定数
end

file4.txt

class Settings < Settingslogic
  source "#{Rails.root}/config/application.yml"
  namespace Rails.env
end

file5.yml

# config/application.yml
defaults: &defaults
  artist:
    band: Oasis
development:
  <<: *defaults
test:
  <<: *defaults
production:
  <<: *defaults

file6.txt

おためしあれん。