An object oriented approach to this problem would be to use a Factory class to instantiate the right object depending on what OS you run your script on (this example will run as is, but in real life you probably want to separate the modules into different files and "require" them in from the factory class as needed, as you'll surely not have your Windows specific CPAN modules on your Unix boxes and vice-versa):

package FooFactory;
use strict;

sub get_foo {

    if ($^O eq 'MSWin32') {
    
        return Win32Foo->new();
    
    } else {
    
        return UnixFoo->new();
    }
}

#=================

package Foo;
use strict;

sub new {
    my $proto = shift;
    my $class = ref($proto) || $proto;

    my $self = {};

    bless ($self, $class);
    return $self;
}

sub bar {

    die "abstract, must override";

}

#=================

package Win32Foo;
use strict;
use vars qw(@ISA);
@ISA=qw(Foo);             

#use Win32::OLE;
#Win32::OLE->import;
                
sub bar {
    
    print "Win32\n";
}

#=================

package UnixFoo;
use strict;
use vars qw(@ISA);
@ISA=qw(Foo);             

sub bar {
    
    print "UNIX\n";
}

#=================

#  USAGE:

my $foo = FooFactory->get_foo();
$foo->bar();
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