Rails need advise on controller practices

I try to follow RESTfull approach in controllers, but sometimes I need action which won't fit into default ones. E.g. I have an index action rendering all articles which is

def index
  @articles = Article.all

but what if I also want search them? should I create separate actions for it, or should I bloat existing controller, like:

def index
    if params[:search]
      @articles = Article.where(id: params[:search_id])
    else
      @articles = Article.all

What is the right way?