zfs snapshot auto-rotation script

zfs_snapshot.sh

#!/bin/sh
#
# zfs snapshot auto-rotation
#
#     usage: zfs_snapshot.sh <mountpoint> <snapshot name> <number of keeping snapshots> [recursive]
#
#       recursive option: Recursively create snapshot (zfs snapshot -r)
#
# for crontab
#
# @daily   /root/bin/zfs_snapshot.sh tank days_later   7  recursive
# @weekly  /root/bin/zfs_snapshot.sh tank weeks_later  5  recursive
# @monthly /root/bin/zfs_snapshot.sh tank months_later 12 recursive
# @yearly  /root/bin/zfs_snapshot.sh tank years_later  10 recursive


PATH=/sbin:$PATH

mountpoint=$1
snapshot_name=$2
level=$3
option=$4

zfs_opt=
if [ "$option" = "recursive" ]; then
    zfs_opt=-r
fi

## destroy outdated snapshot
i_max=`expr $level - 1`
i_test=`zfs list -t snapshot | grep "$mountpoint@$i_max$snapshot_name" | wc -l`
if [ $i_test -gt 0 ]; then
    zfs destroy $zfs_opt "$mountpoint@$i_max$snapshot_name"
fi

## rolling snapshot
j=`expr $level - 2`
#for i in `jot - $j 0`; do
for i in `seq $j -1 0`; do
    i_plus1=`expr $i + 1`
    i_test=`zfs list -t snapshot | grep "$mountpoint@$i$snapshot_name" | wc -l`

    if [ $i_test -gt 0 ] ; then
        zfs rename $zfs_opt "$mountpoint@$i$snapshot_name" "$mountpoint@$i_plus1$snapshot_name"
    fi
done

## take snapshot
zfs snapshot $zfs_opt "$mountpoint@0$snapshot_name"

This may take costs when it has too many snapshots.
If you regard, you can use original.