Shell script to create a CSV file from a MongoDB collection. The CSV file will contain all possible top-level keys. Embedded documents are not handled.

make_csv.sh

#!/bin/bash

function usage {
  printf "Usage:\n$0 <db_name> <collection_name> <output_csv_file>\n"
  exit 1
}

db_name=$1
collection=$2
output_file=$3

[[ -z $collection ]] && usage
[[ -z $db_name ]] && usage
[[ -z $output_file ]] && usage

fields=$(mongo "$db_name" --quiet <<EOF | grep -e "_id,"
mr = db.runCommand({
  "mapreduce" : "$collection",
  "map" : function() {
    for (var key in this) { emit(key, null); }
  },
  "reduce" : function(key, stuff) { return null; }, 
  "out": "$collection" + "_keys"
});
var uniqueFields = db[mr.result].distinct("_id");
print(uniqueFields);
EOF
)

mongoexport --db "$db_name" --collection "$collection" --csv --fields "$fields" --out "$output_file"

printf "CSV contents exported to $output_file\n"