Mongo - compact collection in background

I want to compact very large collection in mongo (around 800GB of data).
I know that I need to run it on separate replicas (first secondaries, then promote another node to primary, and then compact last secondary). And that is fine.
to do this i need to run:

db.runCommand({compact: "collectionName"})

But i want to execute it in background. And this is my problem because when I execute:

mongosh mongodb://database.host.net:27017/databaseName --eval "db.runCommand({compact: "collectionName"})"

I'm getting message:

ReferenceError: collectionName is not defined

How can i run compacting in background ?

The message ReferenceError: collectionName is not defined you're getting is due to how your command is formatted. You need to use different quotes for embedded quotes, otherwise it will cause syntax errors like yours.

Try instead of:

mongosh mongodb://database.host.net:27017/databaseName --eval "db.runCommand({compact: "collectionName"})"

A command:

mongosh mongodb://database.host.net:27017/databaseName --eval 'db.runCommand({compact: "collectionName"})'

Note how I used single quotes ' instead of double quotes " around --eval.

And to run it on background, use this:

nohup mongosh mongodb://database.host.net:27017/databaseName --eval 'db.runCommand({compact: "collectionName"})' & 

& makes a command run on background. And nohup makes a command run even when terminal is closed.