> help
    db.help()                    help on db methods
    db.mycoll.help()             help on collection methods
    sh.help()                    sharding helpers
    rs.help()                    replica set helpers
    help admin                   administrative help
    help connect                 connecting to a db help
    help keys                    key shortcuts
    help misc                    misc things to know
    help mr                      mapreduce

    show dbs                     show database names
    show collections             show collections in current database
    show users                   show users in current database
    show profile                 show most recent system.profile entries with time >= 1ms
    show logs                    show the accessible logger names
    show log [name]              prints out the last segment of log in memory, ‘global‘ is default
    use <db_name>                set current database
    db.foo.find()                list objects in collection foo
    db.foo.find( { a : 1 } )     list objects in foo where a == 1
    it                           result of the last line evaluated; use to further iterate
    DBQuery.shellBatchSize = x   set default number of items to display on shell
    exit                         quit the mongo shell
> 

> db.help()
DB methods:
    db.adminCommand(nameOrDocument) - switches to ‘admin‘ db, and runs command [just calls db.runCommand(...)]
    db.aggregate([pipeline], {options}) - performs a collectionless aggregation on this database; returns a cursor
    db.auth(username, password)
    db.cloneDatabase(fromhost) - deprecated
    db.commandHelp(name) returns the help for the command
    db.copyDatabase(fromdb, todb, fromhost) - deprecated
    db.createCollection(name, {size: ..., capped: ..., max: ...})
    db.createView(name, viewOn, [{$operator: {...}}, ...], {viewOptions})
    db.createUser(userDocument)
    db.currentOp() displays currently executing operations in the db
    db.dropDatabase()
    db.eval() - deprecated
    db.fsyncLock() flush data to disk and lock server for backups
    db.fsyncUnlock() unlocks server following a db.fsyncLock()
    db.getCollection(cname) same as db[‘cname‘] or db.cname
    db.getCollectionInfos([filter]) - returns a list that contains the names and options of the db‘s collections
    db.getCollectionNames()
    db.getLastError() - just returns the err msg string
    db.getLastErrorObj() - return full status object
    db.getLogComponents()
    db.getMongo() get the server connection object
    db.getMongo().setSlaveOk() allow queries on a replication slave server
    db.getName()
    db.getPrevError()
    db.getProfilingLevel() - deprecated
    db.getProfilingStatus() - returns if profiling is on and slow threshold
    db.getReplicationInfo()
    db.getSiblingDB(name) get the db at the same server as this one
    db.getWriteConcern() - returns the write concern used for any operations on this db, inherited from server object if set
    db.hostInfo() get details about the server‘s host
    db.isMaster() check replica primary status
    db.killOp(opid) kills the current operation in the db
    db.listCommands() lists all the db commands
    db.loadServerScripts() loads all the scripts in db.system.js
    db.logout()
    db.printCollectionStats()
    db.printReplicationInfo()
    db.printShardingStatus()
    db.printSlaveReplicationInfo()
    db.dropUser(username)
    db.repairDatabase()
    db.resetError()
    db.runCommand(cmdObj) run a database command.  if cmdObj is a string, turns it into {cmdObj: 1}
    db.serverStatus()
    db.setLogLevel(level,<component>)
    db.setProfilingLevel(level,slowms) 0=off 1=slow 2=all
    db.setWriteConcern(<write concern doc>) - sets the write concern for writes to the db
    db.unsetWriteConcern(<write concern doc>) - unsets the write concern for writes to the db
    db.setVerboseShell(flag) display extra information in shell output
    db.shutdownServer()
    db.stats()
    db.version() current version of the server
> 

> db
test
> 
> show dbs
admin   0.000GB
config  0.000GB
local   0.000GB
> 
> use local
switched to db local
> 
> db
local
> 
> exit
bye
[Anliven@localhost bin]$ 

> 111 + 222
333
> 666 / 111
6
>