bash-based

#!/usr/bin/env bash

trap gexit SIGINT
trap gexit SIGTERM
trap gexit SIGKILL
LOGFILE=$HOME/backup.log


logger() {
    echo $(date '+%Y-%m-%d %H:%M:%S') - $@ | tee -a $LOGFILE
}

gexit() {
    logger Signal received... exiting
    exit 2
}


helpAndExit() {
    cat << EOF

$1

Usage:
    --source source folder to be backed up
    --dest destination folder
    --snapshot Take snapshot on supported filesystems
    --fs (stratis|btrfs) The filesystem of the snapshot

    Options for btrfs
        --btrfs-vol-label The label of the btrfs partition 

    Options for stratis/zfs
        --fs-name The name of the filesystem
        --pool-name The name of the pool

Examples: 
    backup.sh --source / --dest /dst --snapshot --fs zfs --fs-name FS_NAME --pool-name POOL_NAME
    backup.sh --source / --dest /dst --snapshot --fs stratis --fs-name FS_NAME --pool-name POOL_NAME 
    backup.sh --source / --dest /dst


EOF
    exit 1
}

sanityCheck() {
    if  [[ $TAKE_SNAPSHOT == "yes" ]]; then
        if [[ $MODE != "stratis"  &&  $MODE != "btrfs" && $MODE != "zfs" ]] ; then
            helpAndExit "The --fs parameter is required if snapshot requested"
        elif [[ $EUID -ne 0 ]]; then
            helpAndExit "Snapshot requires root"
        fi

    else
        MODE=""
    fi

    if [[ $MODE == "stratis" || $MODE == "zfs" && $FS_NAME == "" ]]; then
        helpAndExit "$MODE filesystem name is required"
    fi

    if [[ $MODE == "stratis" || $MODE == "zfs" && $POOL_NAME == "" ]]; then
        helpAndExit "$MODE pool name is required"
    fi

    if [[ $MODE == "btrfs" && $FS_LABEL == "" ]]; then
        helpAndExit "Filesystem Label is required in case of btrfs"
    fi

    if [[ -z $SOURCE ]]; then
        helpAndExit "Source is required"
    fi

    if [[ -z $DEST ]]; then
        helpAndExit "Dest is required"
    fi

    if ! mountpoint -q $DEST > /dev/null; then
        logger $DEST is not a mounted filesystem
        exit 1
    fi

}

parse_args() {
    POSITIONAL=()
    while [[ $# -gt 0 ]]; do
        key="$1"
        echo $1 $2
        case $key in
            --fs)
                MODE="$2"
                shift # past argument
                shift # past value
                ;;
            --fs-name)
                FS_NAME="$2"
                shift # past argument
                shift # past value
                ;;
            --pool-name)
                POOL_NAME="$2"
                shift # past argument
                shift # past value
                ;;
            --btrfs-vol-label)
                FS_LABEL="$2"
                shift # past argument
                shift # past value
                ;;
            --source)
                SOURCE="$2"
                shift # past argument
                shift # past value
                ;;
            --dest)
                DEST="$2"
                shift # past argument
                shift # past value
                ;;
            --snapshot)
                TAKE_SNAPSHOT="yes"
                shift # past argument
                #shift # past value
                ;;
            --extra)
                EXTRA="$2"
                echo EXTRA $EXTRA
                shift # past argument
                shift # past value
                ;;
            --debug)
                DEBUG="yes"
                shift # past argument
                #shift # past value
                ;;
            --help)
                helpAndExit
                shift # past argument
                #shift # past value
                ;;
            #--default)
                #  DEFAULT=YES
                #  shift # past argument
                #  ;;
            *)    # unknown option
                POSITIONAL+=("$1") # save it in an array for later
                shift # past argument
                logger Unknown option $key $2
                exit 1
                ;;
        esac
    done

    set -- "${POSITIONAL[@]}" # restore positional parameters
}

create_btrfs() {
    return
    mkfs.btrfs -L $LABEL /dev/sd?
    mount /dev/sd? /mnt/tmp
    btrfs subvolume create /mnt/tmp/@rootfs
    mkdir /mnt/tmp/.snapshots
    btrfs subvolume set-default 256 /mnt/tmp
    umount /mnt/tmp
}

snapshotfs() {
    [[ $TAKE_SNAPSHOT != "yes" ]] && return 
    logger Taking Snapshot with $MODE
    TODAY=$(date '+%a')
    SNAPSHOT_TIMESTAMP=$(date '+%a-%Y%m%d')

    if [[ $MODE == "btrfs" ]]; then
        mount_dir=$(mktemp -d -p /mnt)
        mount -o subvolid=5 LABEL=$FS_LABEL $mount_dir
        btrfs subvolume delete $mount_dir/.snapshots/@$TODAY-*   
        btrfs subvolume snapshot $mount_dir/@rootfs $mount_dir/.snapshots/@$SNAPSHOT_TIMESTAMP
        umount $mount_dir
        rmdir $mount_dir
    elif [[ $MODE == "stratis" ]]; then
        local toremove=$(stratis fs | grep ${FS_NAME}-${TODAY} | awk '{print $2}')
        logger Detroying snapshot $toremove
        stratis fs destroy $POOL_NAME ${toremove}
        logger Creating $FS_NAME-$SNAPSHOT_TIMESTAMP
        stratis fs snapshot $POOL_NAME $FS_NAME $FS_NAME-$SNAPSHOT_TIMESTAMP
    elif [[ $MODE == "zfs" ]]; then
        local toremove=$(/sbin/zfs list -t snapshot | grep ${FS_NAME}@${TODAY} | awk '{print $1}')
        if [[ -n $toremove ]]; then
            logger Removing snapshot $toremove
            /sbin/zfs destroy $toremove >> $LOGFILE
        fi
        logger Creating new snapshot $POOL_NAME/$FS_NAME@$SNAPSHOT_TIMESTAMP
        /sbin/zfs snapshot $POOL_NAME/$FS_NAME@$SNAPSHOT_TIMESTAMP >> $LOGFILE 2>>$LOGFILE
    fi
}

doBackup() {
    #Should be run by root
    EXCLUDE_FS=("/dev/*" "/proc/*" "/sys/*" "/tmp/*" "/run/*" "/mnt/*" "/media/*" "/lost+found")
    RSYNC_CMD="/usr/bin/rsync -aAXHuS --delete "
    [[ $DEBUG == "yes" ]] && RSYNC_CMD="$RSYNC_CMD --progress"
    #RSYNC_DELETE="--delete"
    #RSYNC_DELETE_OPTIONS="--delete-before --delete-excluded"

    logger BACKUP started with arguments: $ARGS
    for path in "${EXCLUDE_FS[@]}"; do
        EXCLUDE="$EXCLUDE --exclude=${path}"
    done
    logger Rsyncing...
    $RSYNC_CMD $EXCLUDE $EXTRA $SOURCE $DEST >> $LOGFILE 2>>$LOGFILE
    echo $(date) > $DEST/last_backup
    snapshotfs 
    logger Done.
}

ARGS=$@
parse_args $@
sanityCheck
doBackup