Find by id :

db.test.find({"_id" : ObjectId("4ecc05e55dd98a436ddcc47c")})

Show all ids :

var a = db.c.find({}, {_id:1}).map(function(item){ return item._id; })

Run actions on elements :

 tests.forEach(function(test) {
        if (evaluation.hasOwnProperty('toto')) {
            print('toto was here');
        } else {
            db.tests.save(test);
        }
    });

Run javascript :

load('/tmp/xxx.js');

Connect to database :

db = connect("mongodb://user:password@localhost:27017/lcri?authSource=admin");