How do I do a redirection in routes.rb passing on the query string

You can use request object in this case:

match "/invoices" => redirect{ |p, request| "/dashboard?#{request.query_string}" }

The simplest way to do this (at least in Rails 4) is do use the options mode for the redirect call..

get '/invoices' => redirect(path: '/dashboard')

This will ONLY change the path component and leave the query parameters alone.