######### Main script 
######### index.pl

#!C:/perl5.8/bin/perl.exe
use CGI qw(:cgi);

my $query = get_param('action') || 'default';

# login.pl contains the subroutine do_login()
require "login.pl";

my %actions = (
   default  => \&default,
   login    =>  \&do_login
);

&{ $actions{$query} }

sub default {
  # show default page
}

######### Auxiliary script
######### login.pl

sub do_login {
   #process login
}

1;