How to get the subdomain value from a url?

Question

how can I get the subdomain value in rails, is there a built-in way to do this?

e.g.

test123.example.com

I want the test123 part of

Answer 1

current domain with subdomains:

"#{request.subdomain}.#{request.domain}"
# or
"#{request.subdomains.join(".")}.#{request.domain}"