The following script backs up only files that have changed in the last 15 minutes. It keeps the files from earlier backups and adds only the changed files.
#!/bin/bash dir=$1 dir=$2 for d in $dir1 $dir2 do find "$d" -mmin +15 ! -type d -print > "$d".list tar -cpf - -X "$d".list "$d" | (cd backup; tar xf -) /bin/rm -f $d.list done