gistfile1.rb

class TestClass
  @@var = "a class variable"
  @var = "a class instance variable"
  def self.print
    puts @@var
    puts @var
  end
end
class DerivedTestClass < TestClass
  def self.set_var
    @@var = "a class variable : changed"    
    @var = "a class instance variable : changed"
  end
end
TestClass.print
puts "-------------"
DerivedTestClass.print
puts "-------------"
DerivedTestClass.set_var
DerivedTestClass.print
puts "-------------"
TestClass.print