#put in application_helper.rb :

def section_link(name,options)
    if options[:action] == @current_action and options[:controller] == @current_controller
       link_to(name, options, :class => 'on')
    else
      link_to(name,options)
    end
end

#initialize vars in controller
before_filter :instantiate_controller_and_action_names

def instantiate_controller_and_action_names
      @current_action = action_name
      @current_controller = controller_name
end 

#usage in view:
<%=section_link('Home',:controller => 'articles', :action => 'index')%>

http://snippets.dzone.com/posts/show/2016

note to self

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