Simple Tarsnap backups with Bash.

tarcinch

#!/bin/bash

# tarcinch: simple tarsnap backups with bash.
# run with a systemd.timer, cron, or manually.
# requires: bash, coreutils, grep, and tarsnap.

# https://gist.github.com/ledti/b8bc6bd0200b7c91ea58
# last modified: 2017/05/30

# * monthly backups on the first of the month (if enabled).
#    - if day of month > 1 and ≤ 21 and no current monthly backup, creates backup.
# * weekly backups on mondays (if enabled).
#    - if day of week is > 1 and ≤ 4 and no current weekly backup, creates backup.
# * daily backups otherwise (if enabled).

# archive format: $PREFIX-$TYPE-$(date +%F-%V-%u), see 'man date'
#  e.g. $PREFIX-$TYPE-YEAR-MONTH-DAY-WEEK-DAYS
#  e.g. tarcinch-DAILY-2015-02-04-05-3

# ---

# base tarsnap command:
# e.g. "tarsnap".
TARSNAP="tarsnap --quiet --configfile $HOME/.config/tarsnap/tarsnaprc"

# all stored tarsnap archives:
# * don't change unless you know what you're doing.
ARCHIVES=$($TARSNAP --list-archives)

# file containing a list of filenames to backup to tarsnap:
# * use the full path to each file, and separate them with a space or newline.
LIST="$HOME/.config/tarsnap/synclist"

# prefix for all backups:
# e.g. "tarcinch".
PREFIX="$HOSTNAME"

# number of daily backups to preserve:
# if set to 0, disable daily backups.
KD="4"

# number of weekly backups to preserve:
# if set to 0, disable weekly backups.
KW="3"

# number of monthly backups to preserve:
# if set to 0, disable monthly backups.
KM="2"

# make tarcinch slightly verbose:
# * does not affect tarsnap's output.
# anything but "true" disables verbosity.
VERBOSE="true"

# ---

# transform the backup list into an array and sanitize it for tarsnap:
mapfile -t SYNCLIST < "$LIST"
for file in "${!SYNCLIST[@]}"; do
    # if a file in the array doesn't exist, then:
    if [[ ! -e ${SYNCLIST[$file]} ]]; then
        # report procedure if $VERBOSE is true:
        if [[ $VERBOSE == "true" ]]; then
            echo "Ignoring file that does not exist: ${SYNCLIST[$file]}"
        fi
        # remove non-existent file from the array:
        unset -v "SYNCLIST[$file]"
    fi
done

# preserves a set number of backups:
PRESERVE() {
    # count the number of backups and if it's < the preserved amount, then:
    if [[ $(echo "$ARCHIVES" | grep -c "$PREFIX-$TYPE") -lt $KEEP ]]; then
        # do nothing and exit:
        exit
    fi
}

# prunes older backups:
PRUNE() {
    # determine the oldest tarsnap archive:
    OLDEST=$(echo "$ARCHIVES" | grep "$PREFIX-$TYPE" | sort | head -n 1)
    # report procedure if $VERBOSE is true:
    if [[ $VERBOSE == "true" ]]; then
        echo "Deleting backup: $OLDEST"
    fi
    # delete the oldest tarsnap archive:
    $TARSNAP -d -f "$OLDEST"
}

# creates a daily backup:
DAILY_BACKUP() {
    TYPE="DAILY"
    KEEP="$KD"
    # report procedure if $VERBOSE is true:
    if [[ $VERBOSE == "true" ]]; then
        echo "Creating backup: $PREFIX-$TYPE-$(date +%F-%V-%u)"
    fi
    # create daily backup:
    $TARSNAP -c -f "$PREFIX-$TYPE-$(date +%F-%V-%u)" "${SYNCLIST[@]}"
}

# creates a weekly backup:
WEEKLY_BACKUP() {
    TYPE="WEEKLY"
    KEEP="$KW"
    # report procedure if $VERBOSE is true:
    if [[ $VERBOSE == "true" ]]; then
        echo "Creating backup: $PREFIX-$TYPE-$(date +%F-%V-%u)"
    fi
    # create weekly backup:
    $TARSNAP -c -f "$PREFIX-$TYPE-$(date +%F-%V-%u)" "${SYNCLIST[@]}"
}

# creates a monthly backup:
MONTHLY_BACKUP() {
    TYPE="MONTHLY"
    KEEP="$KM"
    # report procedure if $VERBOSE is true:
    if [[ $VERBOSE == "true" ]]; then
        echo "Creating backup: $PREFIX-$TYPE-$(date +%F-%V-%u)"
    fi
    # create monthly backup:
    $TARSNAP -c -f "$PREFIX-$TYPE-$(date +%F-%V-%u)" "${SYNCLIST[@]}"
}

# determines if there was a previous backup created today:
ANY_CHECK() {
    # count the number of backups made today:
    ACHK=$(echo "$ARCHIVES" | grep -c "$PREFIX-.*-$(date +%F)-.*-.*")
    # if $ACHK ≥ 1, then:
    if [[ $ACHK -ge 1 ]]; then
        # report result if $VERBOSE is true and exit:
        if [[ $VERBOSE == "true" ]]; then
            echo "$ACHK previous backup(s) created today, aborting..."
        fi
        exit
    fi
}

# insure the creation of a monthly backup if it's not too late into the month and $KM ≥ 1:
MONTHLY_CHECK() {
    # count the number of monthly backups made this month:
    MCHK=$(echo "$ARCHIVES" | grep -c "$PREFIX-MONTHLY-$(date +%Y)-$(date +%m)-.*-.*-.*")
    # if $KM ≥ 1 and $MCHK < 1 and the day of the month is > 1 and also ≤ 21, then:
    if [[ $KM -ge 1 && $MCHK -lt 1 && $(date +%-d) -gt 1 && $(date +%-d) -le 21 ]]; then
        # create a monthly backup and exit:
        MONTHLY_BACKUP
        PRESERVE
        PRUNE
        exit
    fi
}

# insure the creation of a weekly backup if it's not too late into the week and $KW ≥ 1:
WEEKLY_CHECK() {
    # count the number of weekly backups made this week:
    WCHK=$(echo "$ARCHIVES" | grep -c "$PREFIX-WEEKLY-$(date +%Y)-.*-.*-$(date +%V)-.*")
    # if $KW ≥ 1 and $WCHK < 1 and the day of the week is > 1 and also ≤ 4, then:
    if [[ $KW -ge 1 && $WCHK -lt 1 && $(date +%u) -gt 1 && $(date +%u) -le 4 ]]; then
        # create a weekly backup and exit:
        WEEKLY_BACKUP
        PRESERVE
        PRUNE
        exit
    fi
}

# in order, run the following:
ANY_CHECK
MONTHLY_CHECK
WEEKLY_CHECK

 # if $KM ≥ 1 and it's the first day of the month, then:
if [[ $KM -ge 1 && $(date +%-d) -eq 1 ]]; then
    MONTHLY_BACKUP
    PRESERVE
    PRUNE
# if $KW ≥ 1 and it's the first day of the week, then:
elif [[ $KW -ge 1 && $(date +%u) -eq 1 ]]; then
    WEEKLY_BACKUP
    PRESERVE
    PRUNE
# if $KD ≥ 1, then:
elif [[ $KD -ge 1 ]]; then
    DAILY_BACKUP
    PRESERVE
    PRUNE
# report result if $KD and $KW and $KM are disabled and $VERBOSE is true:
elif [[ $KD -lt 1 && $KW -lt 1 && $KM -lt 1 && $VERBOSE == "true" ]]; then
    echo "$(( KD + KW + KM )) backup(s) are set to be preserved, aborting..."
fi