Printing Mongo query output to a file while in the mongo shell

2 days old with Mongo and I have a SQL background so bear with me. As with mysql, it is very convenient to be in the MySQL command line and output the results of a query to a file on the machine. I am trying to understand how I can do the same with Mongo, while being in the shell

I can easily get the output of a query I want by being outside of the shell and executing the following command:

mongo localhost:27017/dbname --eval "printjson(db.collectionName.findOne())" > sample.json

The above way is fine, but it requires me to exit the mongo shell or open a new terminal tab to execute this command. It would be very convenient if I could simply do this while still being inside the shell.

P.S: the Question is an offshoot of a question I posted on SO

AFAIK, there is no a interactive option for output to file, there is a previous SO question related with this: Printing mongodb shell output to File

However, you can log all the shell session if you invoked the shell with tee command:

$ mongo | tee file.txt
MongoDB shell version: 2.4.2
connecting to: test
> printjson({this: 'is a test'})
{ "this" : "is a test" }
> printjson({this: 'is another test'})
{ "this" : "is another test" }
> exit
bye

Then you'll get a file with this content:

MongoDB shell version: 2.4.2
connecting to: test
> printjson({this: 'is a test'})
{ "this" : "is a test" }
> printjson({this: 'is another test'})
{ "this" : "is another test" }
> exit
bye

To remove all the commands and keep only the json output, you can use a command similar to:

tail -n +3 file.txt | egrep -v "^>|^bye" > output.json

Then you'll get:

{ "this" : "is a test" }
{ "this" : "is another test" }

We can do it this way -

mongo db_name --quiet --eval 'DBQuery.shellBatchSize = 2000; db.users.find({}).limit(2000).toArray()' > users.json

The shellBatchSize argument is used to determine how many rows is the mongo client allowed to print. Its default value is 20.

If you invoke the shell with script-file, db address, and --quiet arguments, you can redirect the output (made with print() for example) to a file:

mongo localhost/mydatabase --quiet myScriptFile.js > output 

There are ways to do this without having to quit the CLI and pipe mongo output to a non-tty.

To save the output from a query with result x we can do the following to directly store the json output to /tmp/x.json:

> EDITOR="cat > /tmp/x.json"
> x = db.MyCollection.find(...).toArray()
> edit x
>

Note that the output isn't strictly Json but rather the dialect that Mongo uses.

It may be useful to you to simply increase the number of results that get displayed

In the mongo shell > DBQuery.shellBatchSize = 3000

and then you can select all the results out of the terminal in one go and paste into a text file.

It is what I am going to do :)

(from : https://stackoverflow.com/a/3705615/1290746)