while (<STDIN>) {
   chomp;
   if (m/PROBABLECAUSE\w*\((\d+),\s*\w*,\s+(\w*)/) {
      ($id, $key)= ($1, $2);
      push @{$dup{$key}}, $id;  #this is modified!
      # check if any key has init caps (not allowed)
      if ($key =~ m/^[A-Z]\w*/) {
         print "Id: $id - $key\n";
      }
   }
}

print "Duplicated keys:\n";

for my $key (keys %dup) {
   my ($ids, $count) = map {$_, scalar @$_} $dup{$key};
   next unless $count > 1;
   print "$key ($count)\n";
   print "Id: $_\n" for @$ids;
}