Access the mongo Shell Help

In addition to the documentation in the MongoDB Manual, the mongo shell provides some additionalinformation in its “online” help system. This document provides anoverview of accessing this help information.

Command Line Help

To see the list of options and help for starting the mongoshell, use the —help option from the command line:

  1. mongo --help

Shell Help

To see the list of help, in the mongo shell, type help:

  1. help

Database Help

In the mongo shell:

  • To see the list of databases on the server, use the show dbscommand: [1]
  1. show dbs

show databases is an alias for show dbs.

  • To see the list of help for methods you can use on the dbobject, call the db.help() method:
  1. db.help()
  • To see the implementation of a method in the shell, type thedb.<method name> without the parenthesis (()), as in thefollowing example which will return the implementation of the methoddb.updateUser():
  1. db.updateUser
[1]If the deployment runs with access control, the operationreturns different values based on user privileges. SeelistDatabases Behavior for details.

Collection Help

In the mongo shell:

  • To see the list of collections in the current database, use theshow collections command:
  1. show collections

See also

show collections

  • To see the help for methods available on the collection objects(e.g. db.<collection>), use the db.<collection>.help()method:
  1. db.collection.help()

<collection> can be the name of a collection that exists,although you may specify a collection that doesn’t exist.

  • To see the collection method implementation, type thedb.<collection>.<method> name without the parenthesis (()),as in the following example which will return the implementation ofthe save() method:
  1. db.collection.save

Cursor Help

When you perform read operations withthe find() method in themongo shell, you can use various cursor methods to modifythe find() behavior and variousJavaScript methods to handle the cursor returned from thefind() method.

  • To list the available modifier and cursor handling methods, use thedb.collection.find().help() command:
  1. db.collection.find().help()

<collection> can be the name of a collection that exists,although you may specify a collection that doesn’t exist.

  • To see the implementation of the cursor method, type thedb.<collection>.find().<method> name without the parenthesis(()), as in the following example which will return theimplementation of the toArray() method:
  1. db.collection.find().toArray

Some useful methods for handling cursors are:

  • hasNext() which checks whether thecursor has more documents to return.
  • next() which returns the next document andadvances the cursor position forward by one.
  • forEach(<function>) which iterates thewhole cursor and applies the <function> to each document returnedby the cursor. The <function> expects a single argument whichcorresponds to the document from each iteration.

For examples on iterating a cursor and retrieving the documents fromthe cursor, see cursor handling. Seealso Cursor for all available cursor methods.

Wrapper Object Help

To get a list of the wrapper classes available in the mongoshell, such as BinData(), type help misc in themongo shell:

  1. help misc

See also

mongo Shell Methods