time machine like backups using rsync

backup_base.sh

#!/bin/bash
#
# will create new directories each time it is executed with hard links to unchanged files
# exclude file can be used to skip certain files/directories as specified by rsync
#  see the FILTER section of https://linux.die.net/man/1/rsync

SRC=$1
DST=$2

if [ ! \( -d "$DST" -a -d "$SRC" \) ]; then
    echo "must specify valid destination and source"
    exit 1
fi

EXCLUDE=${0%/*}/exclude_empty

if [ ! -z $3 ]; then
    EXCLUDE="$3"
fi

date=$(date "+%Y-%m-%dT%H:%M:%S")
rsync --itemize-changes --modify-window=3601 -aP --link-dest=$DST/current --exclude-from=$EXCLUDE $SRC/* $DST/back-$date
rm -f $DST/current
ln -s $DST/back-$date $DST/current