dump-mongodb-index.js

var cur = db.getCollection('students').getIndexes();

for(var index1 in cur){
    var next = cur[index1];
    if(next["name"] == '_id_') {
        continue;
    }
   var unique = next["unique"] ? true : false;
   print("try{ db.getCollection(\"students\").createIndex("+JSON.stringify(next["key"])+",{unique:"+unique+"},{background:1})}catch(e){print(e)}");
}

https://stackoverflow.com/questions/26458457/mongodb-how-to-mongodump-only-indexes-to-another-mongodb-instance

mongo --quiet mongodb://localhost:27017/mydatabase dump-mongodb-index.js