MongoDB - The mongo Shell, mongo Shell Quick Reference

Posted 2020-08-21 huey

mongo Shell Command History

You can retrieve previous commands issued in the mongo shell with the up and down arrow keys. Command history is stored in ~/.dbshell file. See .dbshell for more information.

 

Command Line Options

The mongo shell can be started with numerous options. See mongo shell page for details on all available options. The following table displays some common options for mongo:

Option	Description
--help	Show command line options
--nodb	Start mongo shell without connecting to a database. To connect later, see Opening New Connections.
--shell	Used in conjunction with a javascript file (i.e. <file.js>) to continue in the mongo shell after running the JavaScript file.  See JavaScript file for an example.

 

Command Helpers

The mongo shell provides various help. The following table displays some common help methods and commands:

Help Methods and Commands	Description
help	Show help.
db.help()	Show help for database methods.
db.<collection>.help()	Show help on collection methods. The <collection> can be the name of an existing collection or a non-existing collection.
show dbs	Print a list of all databases on the server.
use <db>	Switch current database to <db>. The mongo shell variable db is set to the current database.
show collections	Print a list of all collections for current database
show users	Print a list of users for current database.
show roles	Print a list of all roles, both user-defined and built-in, for the current database.
show profile	Print the five most recent operations that took 1 millisecond or more. See database profiler for more information.
show databases	Print a list of all available databases.
load()	Execute a JavaScript file. See Write Scripts for the mongo Shell for more information.

 

Basic Shell JavaScript Operations

The mongo shell provides a JavaScript API for database operations.

In the mongo shell, db is the variable that references the current database. The variable is automatically set to the default database test or is set when you use the use <db> to switch current database.

The following table displays some common JavaScript operations:

JavaScript Database Operations	Description
db.auth()	If running in secure mode, authenticate the user.
coll = db.<collection>	Set a specific collection in the current database to a variable coll, as in the following example: coll = db.myCollection;  You can perform operations on the myCollection using the variable, as in the following example: coll.find();
db.collection.find()	Find all documents in the collection and returns a cursor.  See the db.collection.find() and Query Documents for more information and examples.  See Iterate a Cursor in the mongo Shell for information on cursor handling in the mongo shell.
db.collection.insert()	Insert a new document into the collection.
db.collection.update()	Update an existing document in the collection.
db.collection.save()	Insert either a new document or update an existing document in the collection.
db.collection.remove()	Delete documents from the collection.
db.collection.drop()	Drops or removes completely the collection.
db.collection.createIndex()	Create a new index on the collection if the index does not exist; otherwise, the operation has no effect.
db.getSiblingDB()	Return a reference to another database using this same connection without explicitly switching the current database. This allows for cross database queries.

For more information on performing operations in the shell, see:

• MongoDB CRUD Operations
• mongo Shell Methods

 

Keyboard Shortcuts

The mongo shell provides most keyboard shortcuts similar to those found in the bash shell or in Emacs. For some functions mongo provides multiple key bindings, to accommodate several familiar paradigms.

The following table enumerates the keystrokes supported by the mongo shell:

Keystroke	Function
Up-arrow	previous-history
Down-arrow	next-history
Home	beginning-of-line
End	end-of-line
Tab	autocomplete
Left-arrow	backward-character
Right-arrow	forward-character
Ctrl-left-arrow	backward-word
Ctrl-right-arrow	forward-word
Meta-left-arrow	backward-word
Meta-right-arrow	forward-word
Ctrl-A	beginning-of-line
Ctrl-B	backward-char
Ctrl-C	exit-shell
Ctrl-D	delete-char (or exit shell)
Ctrl-E	end-of-line
Ctrl-F	forward-char
Ctrl-G	abort
Ctrl-J	accept-line
Ctrl-K	kill-line
Ctrl-L	clear-screen
Ctrl-M	accept-line
Ctrl-N	next-history
Ctrl-P	previous-history
Ctrl-R	reverse-search-history
Ctrl-S	forward-search-history
Ctrl-T	transpose-chars
Ctrl-U	unix-line-discard
Ctrl-W	unix-word-rubout
Ctrl-Y	yank
Ctrl-Z	Suspend (job control works in linux)
Ctrl-H (i.e. Backspace)	backward-delete-char
Ctrl-I (i.e. Tab)	complete
Meta-B	backward-word
Meta-C	capitalize-word
Meta-D	kill-word
Meta-F	forward-word
Meta-L	downcase-word
Meta-U	upcase-word
Meta-Y	yank-pop
Meta-[Backspace]	backward-kill-word
Meta-<	beginning-of-history
Meta->	end-of-history

 

Queries

In the mongo shell, perform read operations using the find() and findOne() methods.

The find() method returns a cursor object which the mongo shell iterates to print documents on screen. By default, mongo prints the first 20. The mongo shell will prompt the user to “Type it” to continue iterating the next 20 results.

The following table provides some common read operations in the mongo shell:

Read Operations	Description
db.collection.find(<query>)	Find the documents matching the <query> criteria in the collection. If the <query> criteria is not specified or is empty (i.e {} ), the read operation selects all documents in the collection.
db.collection.find(<query>, <projection>)	The following example selects the documents in the userscollection with the name field equal to "Joe": coll = db.users; coll.find( { name: "Joe" } );  For more information on specifying the <query> criteria, see Specify Query Filter Conditions.
db.collection.find().sort(<sort order>)	Find documents matching the <query> criteria and return just specific fields in the <projection>.  The following example selects all documents from the collection but returns only the name field and the _id field. The _id is always returned unless explicitly specified to not return. coll = db.users; coll.find( { }, { name: true } ); For more information on specifying the <projection>, see Project Fields to Return from Query.
db.collection.find(<query>).sort(<sort order>)	Return results in the specified <sort order>.  The following example selects all documents from the collection and returns the results sorted by the name field in ascending order (1). Use -1 for descending order: coll = db.users; coll.find().sort( { name: 1 } );
db.collection.find( ... ).limit( <n> )	Limit result to <n> rows. Highly recommended if you need only a certain number of rows for best performance.
db.collection.find( ... ).skip( <n> )	Skip <n> results.
db.collection.count()	Returns total number of documents in the collection.
db.collection.find(<query>).count()	Returns the total number of documents that match the query.  The count() ignores limit() and skip(). For example, if 100 records match but the limit is 10, count() will return 100. This will be faster than iterating yourself, but still take time.
db.collection.findOne(<query>)	Find and return a single document. Returns null if not found.  The following example selects a single document in the users collection with the name field matches to "Joe": coll = db.users; coll.findOne( { name: "Joe" } );  Internally, the findOne() method is the find() method with a limit(1).

See Query Documents documentation for more information and examples. See Query and Projection Operators to specify other query operators.

 

Error Checking Methods

Changed in version 2.6.

The mongo shell write methods now integrates the Write Concern directly into the method execution rather than with a separate db.getLastError() method. As such, the write methods now return a WriteResult() object that contains the results of the operation, including any write errors and write concern errors.

Previous versions used db.getLastError() and db.getLastErrorObj() methods to return error information.

 

Administrative Command Helpers

The following table lists some common methods to support database administration:

JavaScript Database Administration Methods	Description
db.cloneDatabase(<host>)	Clone the current database from the <host> specified. The<host> database instance must be in noauth mode.
db.copyDatabase(<from>, <to>, <host>)	Copy the <from> database from the <host> to the <to>database on the current server.  The <host> database instance must be in noauth mode.
db.fromColl.renameCollection(<toColl>)	Rename collection from fromColl to <toColl>.
db.repairDatabase()	Repair and compact the current database. This operation can be very slow on large databases.
db.getCollectionNames()	Get the list of all collections in the current database.
db.dropDatabase()	Drops the current database.

See also administrative database methods for a full list of methods.

 

Opening Additional Connections

You can create new connections within the mongo shell. The following table displays the methods to create the connections:

JavaScript Connection Create Methods	Description
db = connect("<host><:port>/<dbname>")	Open a new database connection.
conn = new Mongo()  db = conn.getDB("dbname")	Open a connection to a new server using new Mongo().  Use getDB() method of the connection to select a database.

See also Opening New Connections for more information on the opening new connections from the mongoshell.

 

Miscellaneous

The following table displays some miscellaneous methods:

Method	Description
Object.bsonsize(<document>)	Prints the BSON size of a <document> in bytes

See the MongoDB JavaScript API Documentation for a full list of JavaScript methods 

 

Additional Resources

Consider the following reference material that addresses the mongo shell and its interface:

• mongo
• mongo Shell Methods
• Database Commands
• Aggregation Reference
• Getting Started Guide

Additionally, the MongoDB source code repository includes a jstests directory which contains numerous mongo shell scripts.