backup shell script

#!/bin/sh
export LANG=C

DATE=`date '+%Y%m%d_%H%M'`
GENERATION=2
BACKUP_PATH='/path/to/backup/dir/'
ARCHIVE_TARGET_DIR='/path/to/target/dir'
ARCHIVED_FILE_NAME=${ARCHIVE_TARGET_DIR##*/}_${DATE}.tar.gz



archive() {
    echo "archive ${ARCHIVE_TARGET_DIR}"
    tar zcf /tmp/${ARCHIVED_FILE_NAME} ${ARCHIVE_TARGET_DIR}
}


delete_old_backup() {
    num=`ls -t ${BACKUP_PATH}${ARCHIVE_TARGET_DIR##*/}_*.tar.gz | wc -l`
    num=`expr ${num} - ${GENERATION}`
    if [ ${num} -gt 0 ]
    then
 echo "deleting ${num} files..."
        for file in `ls -t ${BACKUP_PATH}${ARCHIVE_TARGET_DIR##*/}_*.tar.gz | tail -${num}`
        do
            rm -f ${file}
        done
    fi
}

if archive
then
    mv /tmp/${ARCHIVED_FILE_NAME} ${BACKUP_PATH}
    delete_old_backup
    echo 'backup successful!'
fi