text: show dbs
  use pcat
  show collections
  db.runCommand ( {"isMaster":1 })
  db.runCommand ("isMaster")
  db.isMaster()
  db.isMaster
  db.serverStatus()
  print ( "Current operations:" )
  // just call this function interactively :-)
  db.currentOp()
  db.killOp
  db.products.findOne()
  db.products.ensureIndex({"name": 1})
  print ( "Sorting+" )
  db.products.find({},{name:1}).sort({name:1})
  print ( "Sorting-" )
  db.products.find({},{name:1}).sort({name:-1})
  db.products.find( { "name" : "AC3 Case Red" }).explain()
  db.products.getIndexes()
  db.system.indexes.find()
  db.products.help()
  db.products.stats()
  db.system.namespaces.find()
  use admin
  db.runCommand( { "listDatabases" : 1 } )