I've added a small feature to run a pre-backup script before running the duplicacy backup. I don't have it prevent the backup from running upon failure, but could add that. My use case for this was to be able to mount a ZFS snapshot (the latest one for a dataset) to a fixed mount point before running duplicacy on that mount point. That way duplicacy will only see the changes in the latest snapshot and the snapshot will give an immutable snapshot of the filesystem to avoid problems with files changing while duplicacy is backing up. This is helpful for backing up database files without needing to shutdown the DB (part of the pre-snapshot process handles quiescing the DB first).
I've added a small feature to run a pre-backup script before running the duplicacy backup. I don't have it prevent the backup from running upon failure, but could add that. My use case for this was to be able to mount a ZFS snapshot (the latest one for a dataset) to a fixed mount point before running duplicacy on that mount point. That way duplicacy will only see the changes in the latest snapshot and the snapshot will give an immutable snapshot of the filesystem to avoid problems with files changing while duplicacy is backing up. This is helpful for backing up database files without needing to shutdown the DB (part of the pre-snapshot process handles quiescing the DB first).