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Write Scripts for the mongo Shell

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  • Opening New Connections
  • Differences Between Interactive and Scripted mongo
  • Scripting


The following document pertains to the mongo shell, included in the MongoDB Server Download. For information on the new MongoDB Shell (mongosh) refer to the mongosh documentation.

To understand the differences between the two shells, see Comparison of the mongo Shell and mongosh.

You can write scripts for the mongo shell in JavaScript that manipulate data in MongoDB or perform administrative operation.

This tutorial provides an introduction to writing JavaScript that uses the mongo shell to access MongoDB.

From the mongo shell or from a JavaScript file, you can instantiate database connections using the Mongo() constructor:

new Mongo()
new Mongo(<host>)
new Mongo(<host:port>)

Consider the following example that instantiates a new connection to the MongoDB instance running on localhost on the default port and sets the global db variable to myDatabase using the getDB() method:

conn = new Mongo();
db = conn.getDB("myDatabase");

If connecting to a MongoDB instance that enforces access control, you can use the db.auth() method to authenticate.

Additionally, you can use the connect() method to connect to the MongoDB instance. The following example connects to the MongoDB instance that is running on localhost with the non-default port 27020 and set the global db variable:

db = connect("localhost:27020/myDatabase");


See also:


Starting in version 4.2, the mongo shell provides the method isInteractive() that returns a boolean indicating whether the mongo shell is running in interactive or script mode.

When writing scripts for the mongo shell, consider the following:

  • To set the db global variable, use the getDB() method or the connect() method. You can assign the database reference to a variable other than db.

  • Write operations in the mongo shell use a write concern of { w: 1 } by default. If performing bulk operations, use the Bulk() methods. See Write Method Acknowledgements for more information.

  • You cannot use any shell helper (e.g. use <dbname>, show dbs, etc.) inside the JavaScript file because they are not valid JavaScript.

    The following table maps the most common mongo shell helpers to their JavaScript equivalents.

    Shell Helpers
    JavaScript Equivalents
    show dbs, show databases
    use <db>
    db = db.getSiblingDB('<db>')
    show collections
    show users
    show roles
    db.getRoles({showBuiltinRoles: true})
    show log <logname>
    db.adminCommand({ 'getLog' : '<logname>' })
    show logs
    db.adminCommand({ 'getLog' : '*' })
    cursor = db.collection.find()
    if ( cursor.hasNext() ){;
  • In interactive mode, the mongo shell prints the results of operations including the content of all cursors. In scripts, either use the JavaScript print() function or the mongo specific printjson() function which returns formatted JSON.


    To print all items in a result cursor in mongo shell scripts, use the following idiom:

    cursor = db.collection.find();
    while ( cursor.hasNext() ) {
    printjson( );

From the system prompt, use the mongo shell to evaluate JavaScript.

Use the --eval option to the mongo shell to pass the shell a JavaScript fragment, as in the following:

mongo test --eval "printjson(db.getCollectionNames())"

This returns the output of db.getCollectionNames() using the mongo shell connected to the mongod or mongos instance running on port 27017 on the localhost interface.

You can specify a .js file to the mongo shell, and mongo will execute the JavaScript directly. Consider the following example:

mongo localhost:27017/test myjsfile.js

This operation executes the myjsfile.js script in a mongo shell that connects to the test database on the mongod instance accessible via the localhost interface on port 27017.

Alternately, you can specify the mongodb connection parameters inside of the javascript file using the Mongo() constructor. See Opening New Connections for more information.

You can execute a .js file from within mongosh, using the load() function, as in the following:


This function loads and executes the myjstest.js file.

The load() method accepts relative and absolute paths. If the current working directory of mongosh is /data/db, and the myjstest.js resides in the /data/db/scripts directory, then the following calls within mongosh would be equivalent:



There is no search path for the load() function. If the desired script is not in the current working directory or the full specified path, mongosh will not be able to access the file.

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