Simple backup script, using hard-links and rsync to efficiently backup entire directories

backup.sh

#!/bin/sh

set -e
usage() {
    echo "$0 <backup-media> <source-dir> [<source-dir>...]"
    echo "where backup-media = directory to backup to"
    echo "and source-dir = one or more directories to backup"
}

get_last_id() {
    last_id=`ls -d [0-9]*|tail -1`
    if [ -z "$last_id" ];then
        last_id=1000
        mkdir 1000
    fi
    echo $last_id
}

if [ $# -lt 2 ];then
    usage
    exit
fi

BACKUP_MEDIA=$1
shift 1
BACKUP_SRCS=$*

if [ ! -d "$BACKUP_MEDIA" ];then
    echo "$BACKUP_MEDIA is not a directory"
    exit 1
fi
cd "$BACKUP_MEDIA"

# Last backup id
last_id=`get_last_id`
next_id=$(($last_id + 1))

echo "Cloning last backup $last_id to $next_id"
cp -al $last_id $next_id
touch $next_id

for src in $BACKUP_SRCS; do
    target="$BACKUP_MEDIA/$next_id$src"
    echo "Backup $src to $target"
    [ -d "$target" ] || mkdir -p "$target"
    rsync --delete -F -a "$src"/ "$target"/
done