A ZFS snapshots rotation script

rotate.bash

#!/usr/bin/env bash
# A ZFS snapshots rotation script
# by Akihiro Uchida, CC0 dedicated to the public domain
# see http://creativecommons.org/publicdomain/zero/1.0/
usage="usage: $(basename $0) [-v] filesystem generation"

die() {
    echo "$@" >&2
    exit 1
}

VERBOSE=false
while getopts ":v" opt; do
    case $opt in
        v) VERBOSE=true;;
        *) die $usage;;
    esac
done
shift $((OPTIND - 1))

print() {
    $VERBOSE && echo "$@"
}

if [ $# -ne 2 ]; then
    die $usage
fi
filesystem=$1
generation=$2

pool=$(echo $filesystem | cut -d/ -f1)
if [ -z "$(zpool list $pool 2>/dev/null)" ]; then
    die "zfs pool: $pool does not exist!"
fi
mntpt=$(zfs get -H mountpoint $pool | cut -f3)
path=$(echo $filesystem | sed -e "s|$pool|$mntpt|")
if ! [ -e "$path" ]; then
    die "path to $filesystem: $path does not exist!"
fi

if ! [[ "$generation" =~ ^[0-9]+$ ]]; then
    die "generation: $generation must be numeric value!"
fi

snapshots=$(zfs list -H -t snapshot | grep "$filesystem@" | cut -f1)
delete_list=$(echo "$snapshots" | sort -r | sed -e "1,${generation}d")
for snapshot in $delete_list; do
    print "destroy $snapshot"
    # ignore errors on destroy (snapshots may have non-zero userrefs)
    zfs destroy $snapshot || :
done
exit 0