Merging MongoDB files
what exactly are you trying to accomplish? do you want to have all db on another machine?

then you have to use these export and import it


use mongodump to export all you database (you can use mongodump -d your_db) http://docs.mongodb.org/manual/reference/program/mongodump/
use mongorestore to import it http://docs.mongodb.org/v2.2/reference/mongorestore/


you can also use --collection , -c for exporting/importing individual collections