Migrating data from mongo database to another

I have two database connections docDb and mongoDb each having three databases db1,db2, and db3. I want to read all data from db1 of docDb to db1 of mongoDb in Go using mongo-driver and I want to do the same for other databases as well.

This is what I have so far,

func MigrateData(mongoConnection *mongo.Client, docDbConnection *mongo.Client){
	db1Doc := docDbConnection.Database("db1")
	db1Mongo := mongoConnection.Database("db1")

	coll_doc := db1Doc.Collection("collection_1")
	cursor, err := coll_doc.Find(context.TODO(), bson.M{})
	if err != nil {
		log.Fatal(err)
	}
	var documents []bson.M
	if err = cursor.All(context.TODO(), &documents); err != nil {
		log.Fatal(err)
	}

    coll_mongo := db1Mongo.Collection("collection_1")
}

Now this documents consists of all the documents in collection_1 in db1. But I am not able to figure out how to write these to collection_1 of db1 and skip if the document is already present. I did some research online but all I found was inserting custom-made document objects. But here I am getting type []primitive.M.

1. How do I write these to coll_mongo ( collection_1 in db1 of mongodb)?

2. If I do it this way, I will need to know the collection names beforehand and migrate in between collections, or get a list of collection names and loop through it but this sounds like a workaround or a wrong way to do it. Is there another way in Go and mongo-driver where I can read everything from a database and directly write it to another database ( all collections, all documents )?

execute bash script with Go
first dump db docDb with this bash command
create backup.sh file and put this command in it

mongodump --db=docDb --out=./

and then import data to mongoDb with these commands
create restore.sh file and put in it

mongorestore -d mongoDb -c db1  ./docDb/db1.bson --drop
mongorestore -d mongoDb -c db2  ./docDb/db2.bson --drop 
mongorestore -d mongoDb -c db3  ./docDb/db3.bson --drop 

this is sample code in Go to exec bash command

package main

import (
   "fmt"
   "exec"
   "os"
   "bytes"
   "io"
)

func main() {
    app := "bash backup.sh"
    cmd, err := exec.Run(app, []string{app, "-l"}, nil, "", exec.DevNull, exec.Pipe, exec.Pipe)

    if (err != nil) {
       fmt.Fprintln(os.Stderr, err.String())
       return
    }

    var b bytes.Buffer
    io.Copy(&b, cmd.Stdout)
    fmt.Println(b.String())

    cmd.Close()

    app := "bash restore.sh"
    cmd, err := exec.Run(app, []string{app, "-l"}, nil, "", exec.DevNull, exec.Pipe, exec.Pipe)

    if (err != nil) {
       fmt.Fprintln(os.Stderr, err.String())
       return
    }

    var b bytes.Buffer
    io.Copy(&b, cmd.Stdout)
    fmt.Println(b.String())

    cmd.Close()


}