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The mongo Shell

The mongo shell is an interactive JavaScript interface to MongoDB. You can use the mongo shell to query and update data as well as perform administrative operations.

The mongo shell is a component of the MongoDB distributions. Once you have installed and have started MongoDB, connect the mongo shell to your running MongoDB instance.

Start the mongo Shell and Connect to MongoDB

Prerequisites

Ensure that MongoDB is running before attempting to start the mongo shell.

Open a terminal window (or a command prompt for Windows) and go to your <mongodb installation dir>/bin directory:

cd <mongodb installation dir>/bin

Tip

Adding your <mongodb installation dir>/bin to the PATH environment variable allows you to type mongo instead of having to go to the <mongodb installation dir>/bin directory or specify the full path to the binary.

Local MongoDB Instance on Default Port

You can run mongo shell without any command-line options to connect to a MongoDB instance running on your localhost with default port 27017:

mongo

Local MongoDB Instance on a Non-default Port

To explicitly specify the port, include the --port command-line option. For example, to connect to a MongoDB instance running on localhost with a non-default port 28015:

mongo --port 28015

MongoDB Instance on a Remote Host

To explicitly specify the hostname and/or port,

  • You can specify a connection string. For example, to connect to a MongoDB instance running on a remote host machine:

    mongo mongodb://mongodb0.example.com:28015
    
  • You can use the command-line option --host <host>:<port>. For example, to connect to a MongoDB instance running on a remote host machine:

    mongo --host mongodb0.example.com:28015
    
  • You can use the --host <host> and --port <port> command-line options. For example, to connect to a MongoDB instance running on a remote host machine:

    mongo --host mongodb0.example.com --port 28015
    

MongoDB Instance with Authentication

To connect to a MongoDB instance requires authentication:

  • You can specify the username, authentication database, and optionally the password in the connection string. For example, to connect and authenticate to a remote MongoDB instance as user alice:

    Note

    If you do not specify the password in the connection string, the shell will prompt for the password.

    mongo --host mongodb://alice@mongodb0.examples.com:28015/?authSource=admin
    
  • You can use the --username <user> and --password, --authenticationDatabase <db> command-line options. For example, to connect and authenticate to a remote MongoDB instance as user alice:

    Note

    If you specify --password without the user’s password, the shell will prompt for the password.

    mongo --username alice --password --authenticationDatabase admin --host mongodb0.examples.com --port 28015
    

Connect to a MongoDB Replica Set

To connect to a replica set:

  • You can specify the replica set name and members in the connection string.

    mongo mongodb://mongodb0.example.com.local:27017,mongodb1.example.com.local:27017,mongodb2.example.com.local:27017/?replicaSet=replA
    
  • If using the DNS Seedlist Connection Format, you can specify the connection string:

    mongo "mongodb+srv://server.example.com/"
    

    Note

    Use of the +srv connection string modifier automatically sets the ssl option to true for the connection.

  • You can specify the replica set name and members from the --host <replica set name>/<host1>:<port1>,<host2>:<port2>,... command-line option. For example, to connect to replica set named replA:

    mongo --host replA/mongodb0.example.com.local:27017,mongodb1.example.com.local:27017,mongodb2.example.com.local:27017
    

TLS/SSL Connection

For TLS/SSL connections,

  • You can specify the ssl=true option in the connection string.

    mongo mongodb://mongodb0.example.com.local:27017,mongodb1.example.com.local:27017,mongodb2.example.com.local:27017/?replicaSet=replA&ssl=true
    
  • If using the DNS Seedlist Connection Format, you can include the +srv connection string modifier:

    mongo "mongodb+srv://server.example.com/"
    

    Note

    Use of the +srv connection string modifier automatically sets the ssl option to true for the connection.

  • You can specify --ssl command-line option. For example, to connect to replica set named replA:

    mongo --ssl --host replA/mongodb0.example.com.local:27017,mongodb1.example.com.local:27017,mongodb2.example.com.local:27017
    

See also

For more information on the options used in the connection examples as well as other options, see mongo reference and examples of starting up mongo.

Working with the mongo Shell

To display the database you are using, type db:

db

The operation should return test, which is the default database. To switch databases, issue the use <db> helper, as in the following example:

use <database>

To list the available databases, use the helper show dbs. See also db.getSiblingDB() method to access a different database from the current database without switching your current database context (i.e. db).

You can switch to non-existing databases. When you first store data in the database, such as by creating a collection, MongoDB creates the database. For example, the following creates both the database myNewDatabase and the collection myCollection during the insertOne() operation:

use myNewDatabase
db.myCollection.insertOne( { x: 1 } );

The db.myCollection.insertOne() is one of the methods available in the mongo shell.

  • db refers to the current database.
  • myCollection is the name of the collection.

If the mongo shell does not accept the name of a collection, you can use the alternative db.getCollection() syntax. For instance, if a collection name contains a space or hyphen, starts with a number, or conflicts with a built-in function:

db.getCollection("3 test").find()
db.getCollection("3-test").find()
db.getCollection("stats").find()

The mongo shell prompt has a limit of 4095 codepoints for each line. If you enter a line with more than 4095 codepoints, the shell will truncate it.

For more documentation of basic MongoDB operations in the mongo shell, see:

Format Printed Results

The db.collection.find() method returns a cursor to the results; however, in the mongo shell, if the returned cursor is not assigned to a variable using the var keyword, then the cursor is automatically iterated up to 20 times to print up to the first 20 documents that match the query. The mongo shell will prompt Type it to iterate another 20 times.

To format the printed result, you can add the .pretty() to the operation, as in the following:

db.myCollection.find().pretty()

In addition, you can use the following explicit print methods in the mongo shell:

  • print() to print without formatting
  • print(tojson(<obj>)) to print with JSON formatting and equivalent to printjson()
  • printjson() to print with JSON formatting and equivalent to print(tojson(<obj>))

For more information and examples on cursor handling in the mongo shell, see Iterate a Cursor in the mongo Shell. See also Cursor Help for list of cursor help in the mongo shell.

Multi-line Operations in the mongo Shell

If you end a line with an open parenthesis ('('), an open brace ('{'), or an open bracket ('['), then the subsequent lines start with ellipsis ("...") until you enter the corresponding closing parenthesis (')'), the closing brace ('}') or the closing bracket (']'). The mongo shell waits for the closing parenthesis, closing brace, or the closing bracket before evaluating the code, as in the following example:

> if ( x > 0 ) {
... count++;
... print (x);
... }

You can exit the line continuation mode if you enter two blank lines, as in the following example:

> if (x > 0
...
...
>

Tab Completion and Other Keyboard Shortcuts

The mongo shell supports keyboard shortcuts. For example,

  • Use the up/down arrow keys to scroll through command history. See .dbshell documentation for more information on the .dbshell file.

  • Use <Tab> to autocomplete or to list the completion possibilities, as in the following example which uses <Tab> to complete the method name starting with the letter 'c':

    db.myCollection.c<Tab>
    

    Because there are many collection methods starting with the letter 'c', the <Tab> will list the various methods that start with 'c'.

For a full list of the shortcuts, see Shell Keyboard Shortcuts

.mongorc.js File

When starting, mongo checks the user’s HOME directory for a JavaScript file named .mongorc.js. If found, mongo interprets the content of .mongorc.js before displaying the prompt for the first time. If you use the shell to evaluate a JavaScript file or expression, either by using the --eval option on the command line or by specifying a .js file to mongo, mongo will read the .mongorc.js file after the JavaScript has finished processing. You can prevent .mongorc.js from being loaded by using the --norc option.