elif Block Not Entering as Expected When BACKUP_CRON Is Unset

[LeoColman]

docker-borgmatic/root/etc/s6-overlay/s6-rc.d/svc-cron/run

Lines 43 to 60 in 9a8c38e

	# Disable cron if it's set to disabled.
	if [[ "$BACKUP_CRON" = "false" ]]; then
	echo "Disabling cron, removing configuration"
	# crontab -r # quite destructive
	# echo -n > /etc/crontabs/root # Empty config, doesn't look as nice with "crontab -l"
	echo "# Cron disabled" > /etc/crontabs/root
	echo "Cron is now disabled"
	# Apply default or custom cron if $BACKUP_CRON is unset or set (not null):
	elif [[ -v BACKUP_CRON ]]; then
	BACKUP_CRON="${BACKUP_CRON:-"0 1 * * *"}"
	CRON_COMMAND="${CRON_COMMAND:-"/usr/local/bin/borgmatic --stats -v 0 2>&1"}"
	echo "$BACKUP_CRON $CRON_COMMAND" > /etc/crontabs/root
	echo "Applying custom cron"
	# If nothing is set, revert to default behaviour
	else
	echo "Applying crontab.txt"
	crontab /etc/borgmatic.d/crontab.txt
	fi

The current behavior of the script does not align with the intended functionality. Specifically, the elif [[ -v BACKUP_CRON ]] block is not entered when the BACKUP_CRON variable is unset.

The intended behavior is for the script to handle the case where BACKUP_CRON is not set and to enter the elif block with a default value.

---

Steps to Reproduce

1. Run the script with the BACKUP_CRON environment variable unset.
2. Observe that the elif [[ -v BACKUP_CRON ]] block is not executed, and the script proceeds to the else block instead.

---

Expected Behavior

When the BACKUP_CRON variable is unset, the script should enter the elif block and set BACKUP_CRON to the default value (0 1 * * *) and apply the corresponding cron job.

---

Actual Behavior

When BACKUP_CRON is unset, the script skips the elif block and falls into the else block, applying the default crontab.txt instead.

---

Proposed Fix

Update the condition for the elif block to explicitly handle the unset BACKUP_CRON variable. Suggested change:

elif [[ -z "${BACKUP_CRON+x}" ]]; then
    BACKUP_CRON="${BACKUP_CRON:-"0 1 * * *"}"
    CRON_COMMAND="${CRON_COMMAND:-"/usr/local/bin/borgmatic --stats -v 0 2>&1"}"
    echo "$BACKUP_CRON $CRON_COMMAND" > /etc/crontabs/root
    echo "Applying custom cron"

The [[ -z "${BACKUP_CRON+x}" ]] check ensures that the block is entered when BACKUP_CRON is not set.

---

Current Workaround

The current workaround that I found was to set the default value in the config too:

  backup:
    image: b3vis/borgmatic
    volumes:
      - database:/data/database
      - redmine:/data/redmine
      - ssh:/root/.ssh/
    environment:
      - BORG_PASSPHRASE
      - BACKUP_CRON=0 1 * * * # Remove when https://github.com/borgmatic-collective/docker-borgmatic/issues/375 is fixed
    configs:
      - source: borgmatic-config-redmine
        target: /etc/borgmatic.d/config.yaml