Remove old backups prior to making a new one

src/freedombone

 # the type of backup system used, rsync or obnam
 BACKUP_TYPE='obnam'
 
+# Number of days to keep backups for
+BACKUP_MAX_DAYS=30
+
 # Name of a script used to create a backup of the system on usb drive
 BACKUP_SCRIPT_NAME="backup"
 
       echo -n "}' | awk -F '/' '{print " >> /usr/bin/$BACKUP_SCRIPT_NAME
       echo -n '$2' >> /usr/bin/$BACKUP_SCRIPT_NAME
       echo "}')" >> /usr/bin/$BACKUP_SCRIPT_NAME
+      echo "    obnam forget --keep=${BACKUP_MAX_DAYS}d" >> /usr/bin/$BACKUP_SCRIPT_NAME
       echo '    obnam backup -r $USB_MOUNT/backup/${2} --encrypt-with $MY_BACKUP_KEY_ID ${1}' >> /usr/bin/$BACKUP_SCRIPT_NAME
   else
       # For rsyncrypto usage see http://archive09.linux.com/feature/125322
       echo -n '$2' >> /usr/bin/$BACKUP_TO_FRIENDS_SCRIPT_NAME
       echo "}')" >> /usr/bin/$BACKUP_TO_FRIENDS_SCRIPT_NAME
 
+      echo "  obnam forget --keep=${BACKUP_MAX_DAYS}d" >> /usr/bin/$BACKUP_TO_FRIENDS_SCRIPT_NAME     
       echo -n '  obnam backup -r $SERVER_DIRECTORY/backup/ ' >> /usr/bin/$BACKUP_TO_FRIENDS_SCRIPT_NAME
       echo '--encrypt-with $MY_BACKUP_KEY_ID ' >> /usr/bin/$BACKUP_TO_FRIENDS_SCRIPT_NAME
       echo '${2} ${1}' >> /usr/bin/$BACKUP_TO_FRIENDS_SCRIPT_NAME