Help with PHP eregi alnum if statement

[fbsd_user]

I am trying to test the login id entered from a form.
Checking that the contents are upper or lower case alpha or numeric
0-9
plus the special characters - dash and # pound sign

Code:

if(eregi("([[:alnum:]\#\-]+)", $loginid))
  { print("loginid is alnum"); } else { print("loginid is not
alnum");  }



I get the message "loginid is alnum" no matter what I enter to test.

What is wrong with the statement syntax that it don’t work
correctly?

Thanks for your help