Question

I want to union these lines into one.

devise_for :users do get '/users/sign_out' => 'devise/sessions#destroy' end
devise_for :users, :controllers => { :sessions => 'users'}

I think it should be something like:

devise_for :users do get
    '/users/sign_out' => 'devise/sessions#destroy'
    :controllers => { :sessions => 'users'}
end

please help

Answer 1

No, the two statements are not the same. Note the second call passes a hash as an argument for device_for while the first call passes a block(get '/users/sign_out' => 'devise/sessions#destroy') this is in no way equivalent to what you propose.
If the two statements can be combined into a single one it should be something like:

devise_for :users, :controllers => { :sessions => 'users'} do 
  get '/users/sign_out' => 'devise/sessions#destroy'
end

But this may have a different effect(I am not sure what does device_for do) as it changes the order of execution(instead of executing one statement after the other it executes them at the same time.