## file myapp
use strict;

BEGIN {
    if ($^O eq 'MSWin32') {
        require MyAppWin32
    }
    else {
        require MyAppUnix
    }
}

print "HOME is '", get_home_dir(), "'\n";

## file MyAppWin32.pm
package main;

use Win32::TieRegistry ( Delimiter => '/' );

sub get_home_dir {
    my $key = $Registry->{'HKEY_CURRENT_USER/Software/Microsoft/Windows/' .
                          'CurrentVersion/Explorer/Shell Folders'};
    scalar($key->GetValue('Personal'))
}

1;

## file MyAppUnix.pm
package main;

sub get_home_dir {
    (getpwuid($<))[7]
}

1;