Mongo elimina todos los DBS
mongo --quiet --eval 'db.getMongo().getDBNames().forEach(function(i){db.getSiblingDB(i).dropDatabase()})'
Proud Platypus
mongo --quiet --eval 'db.getMongo().getDBNames().forEach(function(i){db.getSiblingDB(i).dropDatabase()})'// if you have a list of Databases to delete then you may run the following command?
['db1', 'db2', 'db3', 'db4'].forEach(function(i){db.getSiblingDB(i).dropDatabase()})