gistfile1.sh

#!/bin/sh
num=21 # 3 weeks

for h in albert; do
  date=`date +%Y%m%d-%H%M%S`
  dir=/home/backup/$h.d
  manifest=$dir/manifest

  # Find the most recent backup
  touch $manifest
  newest=`tail -n 1 $manifest`
  if [ -z "$newest" ]; then
    linkarg=""
  else
    linkarg="--link-dest=$dir/$newest"
  fi

  # Perform the backup
  rsync $linkarg -a --filter=". $dir/rsync.inc" --filter="- *" $h:/ $dir/$date

  # If we have too many backups, delete the oldest
  lines=`wc -l < $manifest`
  if [ $lines -gt $num ]; then
    oldest=`sed 1q $manifest`
    rm -rf $dir/$oldest
    sed 1d $manifest > $manifest.new
    mv $manifest.new $manifest
  fi

  echo $date >> $manifest
  rm /home/backup/$h && ln -s $h.d/$date /home/backup/$h
done