I need to store part of a subdomain in a variable in order to use it as my root and I can't seem to get it to work.

The URLs would be formed like: martin_branch.dev.testsite.com

And I need root to be /home/martin/martin_branch.dev.testsite.com

The underscore ("_") and stuff afterwards is optional. I'll also need martin.dev.testsite.com to have its root as /home/martin/martin.dev.testsite.com.

Note that the name ("martin") and home folder will vary.

This is what I've got so far:

server {
listen 80;
server_name ~^(.+)_*\.dev\.testsite\.com$;
set $myroot $1;
root /home/$myroot/$host;
}

Thanks in advance!