Allow overriding the default options

[paride]

zfs-auto-snapshot is great for its simplicity, however having the possibility to set the default options would be a great plus. This could be done for example by sourcing /etc/default/zfs-auto-snapshot after setting the opt_ defaults, here:

https://github.com/zfsonlinux/zfs-auto-snapshot/blob/master/src/zfs-auto-snapshot.sh#L46

The /etc/default/zfs-auto-snapshot may in this way override any of those options. This is especially important for people installing the tool from a distribution package, as modifying files installed by a package is generally not a good idea.

[maniac0s]

I second that. For instance I'd like to have predictable file names for the snap created including the exact date string, so I can zfs send the created snapshot to a backup system as soon as it was created.

[paride]

Another solution could be using the shell parameter expansion, like this:

: "${opt_backup_full:=}"
: "${opt_backup_incremental:=}"
: "${opt_default_exclude:=1}"
[...]

to allow the variables to be overridden from the environment. The crontab entries should then source the defaults file before running zfs-auto-snapshot. This solution allows easy integration with systemd timers and service files.

Warning: I didn't test any of this :)