sanoid -> shadow symlinker

#!/usr/bin/env bash
#
# Create symbolic links from sanoid's autosnaps
# to something that samba's vfs_shadow_copy2 can read
#
# This script should be run from a directory at the root
# of a ZFS filesystem
#
# Known caveats:
# will break if sanoid creates snapshots with spaces
# or funny characters in the snapshot names
#

set -e

target_snaproot=$(cd $(dirname "$0"); pwd)
zfs_snaproot=$(cd "$target_snaproot/../.zfs/snapshot"; pwd)


# bail if we can't find ZFS's snapshot directory
[ -d "$zfs_snaproot" ] || ( echo "ZFS snap dir $zfs_snaproot not found" ; exit )

while read snapdate;
do
  source_snapdir=""
  target_snapdir="$target_snaproot/$snapdate"

  # determine which snapshot to symlink for a given date
  # i.e. if an there is a yearly and monthly snapshot for the same date, use the yearly one
  if [ -d "$zfs_snaproot/autosnap_${snapdate}_yearly" ] ; then
    source_snapdir="$zfs_snaproot/autosnap_${snapdate}_yearly" ;
  elif [ -d "$zfs_snaproot/autosnap_${snapdate}_monthly" ] ; then
    source_snapdir="$zfs_snaproot/autosnap_${snapdate}_monthly" ;
  elif [ -d "$zfs_snaproot/autosnap_${snapdate}_daily" ] ; then
    source_snapdir="$zfs_snaproot/autosnap_${snapdate}_daily" ;
  elif [ -d "$zfs_snaproot/autosnap_${snapdate}_hourly" ] ; then
    source_snapdir="$zfs_snaproot/autosnap_${snapdate}_hourly" ;
  fi;

  # this shouldn't happen - but check the next date if we
  # don't find one of sanoid's snapdirs
  [ -z "$source_snapdir" ] && continue;

  echo ln -sf "$source_snapdir" "$target_snapdir"
  ln -sf "$source_snapdir" "$target_snapdir"

done < <( cd "$zfs_snaproot"; ls -1 -d autosnap* | perl -ne '/autosnap_(.+)_(monthly|hourly|yearly|daily)/; print "$1\n";' | sort -u )