Deleting everything in a test MongoDb is a common operation for test and dev machine and it is a relative simple operation that I described here. After a little while I got really tired every time to search my gist or into my hd the little script that deletes everything , thus I decided to store it inside the admin db.
The solution is really really simple, just connect to the admin database and register a server side function to delete all databases.
Once the function is saved, you should see it from a GUI tool like Robo 3T.
Figure 1: DeleteAllDb function stored inside the admin database.
Now you can simply load all functions from the Shell and execute the new DeleteAllDbFunction.
And now you can avoid looking around from the script, just invoke DeleteAllDb(db) function from the shell and you will delete all db, except Admin and Local.