var database = "sample";
  var collection = "tests";

  var connections = [];

  config = db.getMongo().getDB("config");
  config.shards.find().forEach(
      function (shard,_a,_i) {
          connections.push(new Mongo(shard["host"]));
      }
  );

  db.getMongo().getDB(database).getCollection(collection).find().forEach(
      function (doc, _a, _i) {
          count = 0;
          onshards = [];
          connections.forEach(
              function(con, _a, _i) {
                  if (con.getDB(database).getCollection(collection).find(doc).count()==1) {
                      count += 1;
                      onshards.push(con);
                  }
              }
  );
          if (count > 1) {
              print("duplicate doc: "+doc['_id']+" found on: ");
              onshards.forEach(function(shard,_a,_i) {print(shard.toString())});
          }
      }
  );