My rsync-based backup script

gistfile1.sh

#! /bin/zsh
# Backup script written by Greg Sexton

# bomb out on first non-zero exit code
set -e
trap 'echo !!! BACKUP EXITED WITH ERROR STATUS !!!' ERR

DATE=$(date "+%Y-%m-%dT%H:%M:%S")
ROOT=/mnt/backup
BACKUP_PREFIX="bak-"
WIP_PREFIX="inprogress-"
DEST=$ROOT/$BACKUP_PREFIX$DATE
WIPDEST=$ROOT/$WIP_PREFIX$DATE
LATEST=$ROOT/latest
INCLUDES=/etc/backup
EXCLUDES=/etc/backup-excludes
MIN_SPACE=10000000 #10G
MIN_INCREMENTS=14

echo "\n*** Starting backup at $DATE"

# Precondition: there should be something mounted on $ROOT
mount|grep -q $ROOT
echo "There is a mount point at $ROOT"

# Possibly remove the oldest incremental backup
INC_COUNT=$(ls -1d $ROOT/$BACKUP_PREFIX*|wc -l)
echo "There are $INC_COUNT incremental backups on $ROOT"
if [[ $INC_COUNT -gt MIN_INCREMENTS ]]
then
    OLDEST_BACKUP=$(find $ROOT -maxdepth 1 -name "$BACKUP_PREFIX*"|sort|head -1)
    echo "Removing: $OLDEST_BACKUP"
    rm -rf $OLDEST_BACKUP
    echo "Successfully removed $OLDEST_BACKUP"
fi

# Check min space threshold. rsync makes it difficult (without
# parsing) to get the exact space requirement. Use this as a simple
# heuristic instead.
if [[ $(df --output=avail $ROOT|sed -e '1d') -lt $MIN_SPACE ]]
then
    echo "The backup volume does not meet the minimum free space requirement."
    false
fi

# Backup
for source in $(cat $INCLUDES)
do
    LINKDEST=""
    if [[ -e $LATEST ]]; then; LINKDEST="--link-dest=$LATEST${source%/}"; fi

    echo "* Backing up $source to $DEST"
    rsync -ax --stats $LINKDEST \
        --delete --delete-excluded \
        --exclude-from=$EXCLUDES \
        ${source%/}/ $WIPDEST${source%/}
done

# Ensure everything is flushed
sync

# Bookkeeping
mv -v $WIPDEST $DEST
rm -vf $LATEST
ln -s $DEST $LATEST

echo "*** Successfully finished backup at $(date "+%Y-%m-%dT%H:%M:%S")"