#!/usr/bin/perl

use strict;
use warnings;

if ($^O eq 'MSWin32')
{
    eval q(
        require module1;
        import  module1;
        sub bar { print "Win32\n"; }
        );
}
else
{
    eval q(
        require module2;
        import  module2;
        sub bar {print "not Win32\n"; }
        );
}

#later in the program...
#we don't care what OS is running -- implementation details are hidden
bar();