Rails: redirect to current path but different subdomain

An even simpler option without the need to do a string sub or specify the controller or action would be to use

redirect_to url_for(subdomain: 'www', only_path: false)

ActionController::Redirecting#redirect_to allows you to pass an absolute URL, so the easiest thing to do would be to pass it one with something like:

redirect_to request.url.sub('blog', 'www')

A simple choice to redirect from subdomain to subdomain would be the following

redirect_to subdomain: 'www', :controller => 'www', :action => "index"

This would be called on a domain name for example foo.apple.com would then go to www.apple.com