Rails Constant and Global Variables（Rails的常量和全域變數）

在Rails下定義常量和全域變數的方法如下，如果你希望任何環境（開發，測試，產品）下都可以訪問的話，則定義在config/environment.rb中
如：
BOOLEN_TRUE=1
如果你希望你的全域變數根據環境來決定，則根據需要在下面的環境中配置
/config/environments/development.rb
/config/environments/test.rb
/config/environments/production.rb

注意，
1> 常量和全域變數必須全部為大寫；
2> 設定了全域常量和變數後需重新啟動伺服器以載入新的設定。

PS. english version

I was recently faced with a common problem that I wanted to share. 
During development there are times you need to specifiy a global or
constant variable that will be shared throughout the entire
application.  In ColdFusion you would normally place something like this in Application.cfm.  In Rails I was uncertain how exactly to approach this.  At first I thought an application.rb file made sense, but the more I thought about it I decided to take advantage of the config files.

Since my global variable was one that would be consistent regardless
of environment (dev, test, and prod) I decided to place it in
config/environment.rb.  I placed this under the RAILS_GEM_VERSION constant:

# Specifies gem version of Rails to use when vendor/rails is not present
RAILS_GEM_VERSION = ‘1.1.2′
BASE_URL = ‘http://mydomain.com/’

Now referencing this in any view can be done similar to any other variable:

<%= BASE_URL %>

If you need to specify globals that are specific to environment then I recommend placing them in their appropriate config file:

/config/environments/development.rb
/config/environments/test.rb
/config/environments/production.rb

From: http://www.db75.com/new_blog/?p=262