simple differential backup based on tar

backup.sh

#!/bin/sh

DATE=`date +%Y-%m-%d__%H-%M`
BACKUP_NAME=$DATE.tar.gz
DIR_TO_BACKUP='dir/to/backup'

# next differential backup
tar -czg snapshot.snar -f $BACKUP_NAME $DIR_TO_BACKUP 

full_backup.sh

#!/bin/sh

# Run this file only once

BACKUP_NAME=full.tar.gz
DIR_TO_BACKUP='dir/to/backup'

# first full backup
tar -czg snapshot.snar -f $BACKUP_NAME $DIR_TO_BACKUP 

cp snapshot.snar snapshot.snar.bak

restore.sh

#!/bin/sh

# Use:
# to restore directory do date `2020-06-25__11-18` :
# ./restore.sh -d 2020-06-25__11-18
# date format see file backup.sh line 3
#

# get date from CLI

DATE=

while getopts d: option
do
case "${option}"
in
d) DATE=${OPTARG};;
esac
done

# restore full backup first
tar -xzpf full.tar.gz


# loop thru files with incremental backups

for FILE in `find . -name "*.tar.gz" ! -name "full.tar.gz" -type f -printf "%f\n" | sort -n`
do
    tar --incremental -xzpf ${FILE}
    if [ $DATE'.tar.gz' = $FILE ]
        then
            break
    fi
done