use strict;
use warnings;
 
my @array=qw/a b c d/; 
my $diff = join"",map{s/(\d+)/$array[$1]/g;$_.$/}grep{eval$_<0}glob("{".join(",",0..$#array)."}-{".join(",",0..$#array)."}");
my $prod = $diff;
$prod =~ tr/-/./;
print "Differences:\n$diff\nProducts:\n$prod";