adding anchor in the controller

I'd like to rewrite a URL that is passed to me by turning the
parameter into an anchor tag. In other words, if the user requests:

/my_controller?q=123

I will handle it in the index action, but I want the user's browser to
show this URL instead:

/my_controller#123

I know I could redirect to a different action. The following works:

def index
  # do stuff
end

def query
  anchor = params[:q]
  redirect_to(:action => 'index', :anchor => anchor)
end

Now if the user requests:

/my_controller/query?q=123

Their browser will say:

/my_controller#123

but how do I do it if I'm already in the correct action?

I’d like to rewrite a URL that is passed to me by turning the

parameter into an anchor tag. In other words, if the user requests:

/my_controller?q=123

Does the user click on a link that contains the above URL?

-Conrad