match(%r{/host/(.*$)}).
        to(:controller => 'home',
               :action => 'host', :host => "[1]").name(:host)

url(:host, "foo.com")

had to use regex because

match('/host/:host').
        to(:controller => 'home',
               :action => 'host').name(:host)

doesn't mach
/host/foo.something.com