MongoDB Sample MapReduce in a file with usage

run.sh

#!/bin/bash
mongo localhost:27017/data_gatherer test.js

test.js

var map = function(){
  emit(this.url, 1);
}
var reduce = function(key, values){
  var res = 0;
  values.forEach(function(v){ res += 1});
  return {count: res};
}

db.sites.mapReduce(map, reduce, { out: "mapped_urls" });