Possible Duplicate:
Where to put Global variables in Rails 3
Is it possible to set Site-Wide Global Variables in Ruby on Rails?
Possible Duplicate:
Where to put Global variables in Rails 3
Is it possible to set Site-Wide Global Variables in Ruby on Rails?
It is bad practice
$my_global_var = "I am very bad variable!"
You can use general Ruby syntax $var_name, but I don't know any case when global variable is a best approach.