my $factory = Config::Builder->new qw(
  user => user
  admin => admin
  htmldir => %path $basedir html
  userdir => %path $htmldir $user
  admindir => %path $htmldir $admin
  email => %join $username @ $domain
);

my $values = read_your_config_file(); # returns a hash of values
my $config = $factory->make_config($values);

print "user dir is ".$config->("userdir")."\n";
print "admin dir is ".$config->("userdir")."\n";