MongoDB drop every database

Try this command:

mongo --quiet --eval 'db.getMongo().getDBNames().forEach(function(i){db.getSiblingDB(i).dropDatabase()})'

You can also do this with a simple mongo command:

db.adminCommand("listDatabases").databases.forEach( function (d) {
    if (d.name != "local" && d.name != "admin"  && d.name != "apiomat"  && d.name != "config")
        db.getSiblingDB(d.name).dropDatabase();
 })

Start mongosh to execute this.

db
  .getMongo()
  .getDBNames()
  .filter(n => !['admin','local','config'].includes(n))
  .forEach(dname =>
    db
      .getMongo()
      .getDB(dname)
      .dropDatabase()
  )
;

One-liner

db.getMongo().getDBNames().filter(n => !['admin','local','config'].includes(n)).forEach(dname => db.getMongo().getDB(dname).dropDatabase());

This drops all DBs but preserves MongoDB's internal collections.

Save this to drop_all_dbs.js:

var databases = db.getMongo().getDBNames()
for(var i in databases){
    db = db.getMongo().getDB( databases[i] );
    if(db.getName() == "admin" || db.getName() == "local"){
        print("skipping db " + db.getName())
        continue
    }
    print( "dropping db " + db.getName() );
    db.dropDatabase();
}

Now you can execute:

mongo drop_all_dbs.js

and all databases (except for admin and local) will be dropped.

This answer is a copy of ALoR's one, just fix drop of system dbs

Adding to @ALoR's answer, for convenience you can put the following in ~/.mongorc.js

function dropDatabases(){
    var mongo = db.getMongo();

    var dbNames = mongo.getDBNames();
    for (var i = 0; i < dbNames.length; i++) {
        var db = mongo.getDB( dbNames[i] );

        print( "Dropping database " + db.getName() + "..." );
        db.dropDatabase();
    }
}

Then at the mongo shell you can simply do

dropDatabases()

From the docs:

Mongo will read the .mongorc.js file from the home directory of the user invoking mongo. In the file, users can define variables, customize the mongo shell prompt, or update information that they would like updated every time they launch a shell.

You can do it easy through c# official driver:

var _mongoServer = MongoServer.Create("mongodb://localhost:27020");

var names = _mongoServer.GetDatabaseNames();
foreach (var name in names)
{
   _mongoServer.DropDatabase(name);
}

Here is a oneliner that allows you to filter for specific names:

for (const dbName of db.getMongo().getDBNames().filter(dbName => dbName.startsWith('test-'))) {console.log(dbName); const dbToDelete = db.getMongo().getDB( dbName ); dbToDelete.dropDatabase()}

This is what worked best for me.

Save this to a file called drop_most_databases.js:

const databasesToSkip = ['admin', 'local', 'config'];
db.getMongo()
  .getDBNames()
  .forEach((dbname) => {
    if (databasesToSkip.includes(dbname)) {
      print(`Skipping ${dbname}`);
    } else {
      print(`Dropping ${dbname}...`);
      db.getMongo().getDB(dbname).dropDatabase();
    }
  });
print(`Now, the only databases that remain are:`);
db.getMongo()
  .getDBNames()
  .forEach((dbname) => {
    print(dbname);
  });

From Terminal, run mongo drop_most_databases.js.