Export all of Mongodb collections as csv without the need to specify fields

mongo-dump-csv.sh

OIFS=$IFS;
IFS=",";

# fill in your details here
dbname=DBNAME
user=USERNAME
pass=PASSWORD
host=HOSTNAME:PORT

# first get all collections in the database
collections=`mongo "$host/$dbname" -u $user -p $pass --eval "rs.slaveOk();db.getCollectionNames();"`;
collections=`mongo $dbname --eval "rs.slaveOk();db.getCollectionNames();"`;
collectionArray=($collections);

# for each collection
for ((i=0; i<${#collectionArray[@]}; ++i));
do
    echo 'exporting collection' ${collectionArray[$i]}
    # get comma separated list of keys. do this by peeking into the first document in the collection and get his set of keys
    keys=`mongo "$host/$dbname" -u $user -p $pass --eval "rs.slaveOk();var keys = []; for(var key in db.${collectionArray[$i]}.find().sort({_id: -1}).limit(1)[0]) { keys.push(key); }; keys;" --quiet`;
    # now use mongoexport with the set of keys to export the collection to csv
    mongoexport --host $host -u $user -p $pass -d $dbname -c ${collectionArray[$i]} --fields "$keys" --csv --out $dbname.${collectionArray[$i]}.csv;
done

IFS=$OIFS;

@adamtaiti here is code with fix for exporting dates:

keys=mongo $dbname --host "$host" --port "$port" -u "$user" -p "$pass" --authenticationDatabase "$authdb" --ssl --eval "function z(c,e){if(c===null || c === undefined || c instanceof Date){return e};var a=[];var d=Object.keys(c);for(var f in d){var b=d[f];if(b != undefined && c != undefined && typeof c[b]==='object'){var g=[],h=z(c[b],e+'.'+b);a=g.concat(a,h);}else a.push(e+'.'+b);}return a;}var a=[],b=db['$col'].findOne({}),c=Object.keys(b);for(var i in c){var j=c[i];if(typeof b[j]==='object'&&j!='_id'){var t1=[],t2=z(b[j],j);a=t1.concat(a,t2);}else a.push(j);}a.join(',');" --quiet;

I'm unable to retrieve the Id, because of the following error
"2022-02-08T13:30:02.767-0500 I CONTROL [thread1] machdep.cpu.extfeatures unavailable _id"