#! perl -slw
use strict;
use warnings;

package xtest::mac;
sub get_answer{ 'Apple' }
package xtest::sun;
sub get_answer{ 'Sun' }
package xtest::aix;
sub get_answer{ 'IBM' }
package xtest::win;
sub get_answer{ 'Win' }
package xtest;
if( $^O =~ m[(dar|sol|aix|win)]i ) {
     ## Export to main for testing only. 
     *main::get_answer = \&{"xtest::\L$1\E::get_answer"};
}
else {
	die 'Unknown OS';
}
1;

##</code><code>##

P:\test>perl -Mxtest -e"print get_answer()"
Win