package aaa;
use constant HELLO=> 'world';
use constant PUNCTUATION=> '!';
sub new { #std constructor here }

package bbb;
our @ISA= qw( aaa );
use constant HELLO=> 'universe';

package main;
my $a= aaa->new();
my $b= bbb->new();

print "\n Hello " . $a->HELLO . $a->PUNCTUATION ;
print "\n Hello " . $b->HELLO . $b->PUNCTUATION ;