How to rename a document field in a MongoDB? [duplicate]

Question

How is possible to rename a field in multiples documents in a MongoDB? I have a collections with elements like this, and I want the rename the field "name" by "userName" in all the collection

{
    "name"       : "luisPerez",
    "address"    : "Gaiman",
    "addressFmt" : "Gaiman, Chubut Province, Argentina",
    "loc" : {
        "type" : "Point",
        "coordinates" : [ -65.4920111, -43.2895976  ]
    }, 
}

Answer 1

You may use rename operator to rename your fields

db.coll.update({}, {$rename:{"name":"userName"}}, false, true);

false : upsert:false
true : multi:true 

Answer 2

Posible duplicity with:

How can I rename a field for all documents in MongoDB?

Posible use $rename

db.collection({}, {$rename:{"name":"userName"}}, false, true);