getting subdomain url

[eluser]vineetyadav[/eluser]
hi,
i am working on application that uses user pages.
forexample if my site is example.com
i have set cname record *.example.com -> example.com
now, suppose if john opens, johnMcCain.example.com, i need to get value johnMcCain from url.

can some one help, please, its urgent