Dynamic root with subdomain not working with Nginx

Dynamic root with subdomain not working with Nginx

I tried everything I could, I can not make it work.
I'd like to redirect my subdomains to a specific folder in my Debian
server using NGinx, here's the configurations I tried :
server {
listen 8080;
server_name ~^(?<user>.+)\.example\.net$;
root /srv/www/example.net/$user;
}
=> error is :
Starting nginx: [emerg]: unknown "user" variable configuration file
/etc/nginx/nginx.conf test failed
(note: I also tried without the ^ as indicated here : Nginx server_name
regexp not working as variable)
If I try this instead :
server {
listen 8080;
server_name *.example.net$;
root /srv/www/example.net/$1;
}
Error is on the request :
2013/08/20 15:38:42 [error] 5456#0: *6 directory index of
"/srv/www/example.net//" is forbidden, client: xxx.xxx.xxx.xxx, server:
*.example.net, request: "GET / HTTP/1.1", host: "test.example.net:8080"
Aka, $1 is empty !
The documentation is wrong then :
http://nginx.org/en/docs/http/server_names.html