How to get mongo command results in to a flat file

Question

How do I export the results of a MongoDB command to a flat file

For example, If I am to get db.collectionname.find() into a flat file.

I tried

Answer 1

Having missed the db needing to be the actual db in Peshkira's answer, here is a general syntax for a one liner in shell (assuming no password):

mongo : --eval "var x = ..; while(x.hasNext()) { printjson( x.next() ) }" >> out.txt

I tested it both on my mac and Google cloud Ubuntu 15 with Mongo 3+.