export_indexes.js

db.adminCommand({'listDatabases':1, nameOnly:true}).databases.forEach(function(mydb) {
    var dbName = mydb.name;
    if (! ["admin", "config", "local"].includes(dbName)) {
        var currentDB = db.getSiblingDB(dbName);
        var collectionNames = currentDB.getCollectionNames();
        collectionNames.forEach(function (collName) {
            if (/^system\./.test(collName)){
              return;
            }
            var indexes = currentDB[collName].getIndexes();
            //print(`    ${collName} ${indexes}`);
            indexes.forEach(function(index){
                delete index.v;
                delete index.ns;
                var key = index.key;
                delete index.key
                print(`db.getSiblingDB('${dbName}').${collName}.createIndex(${JSON.stringify(key)}, ${JSON.stringify(index)})`)
            });
        });
    }
});