Run the following script every Friday:
if test -f /etc/foo then rm -f /etc/foo else touch /etc/foo exit 0 fi
I use this in my weekly backup to alternate which remote directory to save to:
# alternate between dump directories each week # argument evaluates to 0 or 1 /usr/local/sbin/backup-smb $((`/bin/date +%-U` % 2))
The 0 or 1 is used as part of the directory name in my backup-smb script.
