Currently if you want to customise the script for different system it requires manually changing the backup.sh script. This works fine however if the script is ever updated to include new features then those who have manually changed their script will need to adjust their changes to meet the new version.

Making use of named arguments would resolve this and allow for certain settings to be defined when the script is executed, for example:

./backup.sh --from /etc/letsencrypt --to /var/backups/letsencrypt --keep-for 120

A --help flag should be added to list all of the definitions.