my %file_sig;
find( \&find_dup, $root_dir);

sub find_dup
{
   my $name = $_;
   my $full_name = $File::Find::name;
   my $dir = $File::Find::dir;

   if (-f $name) {
      open IN, "<$full_name";
      my $digest = Digest::MD5->new->addfile(*IN)->hexdigest;
      close IN;
      if (exists $file_sig{ $digest }) {
         print "$full_name is a duplicate of $file_sig{ $digest }\n";
      }
      else {
         $file_sig{ $digest } = $full_name;
      }
   }
}