Capturing the output of a job-exec using Docker labels?

[gremo]

Using Docker labels:

labels:
    ofelia.enabled: "true"
    ofelia.job-exec.backup-db.schedule: "@every 15s"
    ofelia.job-exec.backup-db.command: "echo 'hello' > foo.sql"

I'd like to capture the output of the command (i.e. mysqldump command)). I find hard to understand where foo.sql is placed?