ZFS Backup Tool Part 2

I will start with the snapshot names. The part after the @. Those start with zfs-auto-snap so “zfs-auto-snap” will match it.

The next section is which timer made the snapshot. This section can also be called the increment. The valid timers are yearly, monthly, weekly, daily, hourly, and frequent for a default install of zfs-auto-snapshot. The regex “yearly|monthly|weekly|daily|hourly|frequent” will match these timers. However, I would like to get which timer created the snapshot without further parsing. That is the perfect job for a capturing sub match. After adding the capturing sub match, the regex looks like “(?P<increment>yearly|monthly|weekly|daily|hourly|frequent)”.

The final section is the timestamp of the snapshot. Like with the timer section, it is useful not to have to parse this data a second time. With the sub matches “

(?P<year>[[:digit:]]{4})-(?P<month>[[:digit:]]{2})-(?P<day>[[:digit:]]{2})-(?P<hour>[[:digit:]]{2})(?P<minute>[[:digit:]]{2})

” will work.

With the snapshot names completed, I need to capture the zfs tree structure before the @ symbol. I haven’t found a reliable regular expression that will capture that tree but “(?:[[:word:]-.]+)+(?:/?[[:word:]-.]+)*” will recognize a subset of all valid zfs trees. Avoid using anything it won’t recognize, or you may end up with inaccessible files.

package main

import (
	"bufio"
	"fmt"
	"os"
	"regexp"
)

const zfsRegexStart string = "zfs-auto-snap"
const zfsRegexIncrement string = "(?P<increment>yearly|monthly|weekly|daily|hourly|frequent)"
const zfsRegexDateStamp string = "(?P<year>[[:digit:]]{4})-(?P<month>[[:digit:]]{2})-(?P<day>[[:digit:]]{2})-(?P<hour>[[:digit:]]{2})(?P<minute>[[:digit:]]{2})"

var zfsRegex = regexp.MustCompile(zfsRegexStart + "_" + zfsRegexIncrement + "-" + zfsRegexDateStamp)

func testSnapshot(possible string, increment string) (bool, bool) {
	var matches = zfsRegex.FindStringSubmatch(possible)
	if matches == nil {
		return false, false
	}
	var isASnapshot = true
	if matches[1] == increment {
		return isASnapshot, true
	}
	return isASnapshot, false
}

func isAYearlySnapshot(possible string) bool {
	_, isYearly := testSnapshot(possible, "yearly")
	return isYearly
}

func isAMonthlySnapshot(possible string) bool {
	_, isMonthly := testSnapshot(possible, "monthly")
	return isMonthly
}

func isAWeeklySnapshot(possible string) bool {
	_, isWeekly := testSnapshot(possible, "weekly")
	return isWeekly
}

func isADailySnapshot(possible string) bool {
	_, isDaily := testSnapshot(possible, "daily")
	return isDaily
}

func isAnHourlySnapshot(possible string) bool {
	_, isHourly := testSnapshot(possible, "hourly")
	return isHourly
}

func isAFrequentSnapshot(possible string) bool {
	_, isFrequent := testSnapshot(possible, "frequent")
	return isFrequent
}

const poolNameRegex string = "(?:[[:word:]-.]+)+(?:/?[[:word:]-.]+)*"

var snapshotLineRegex = regexp.MustCompile("^" + poolNameRegex + "@" + zfsRegex.String() + ".*$")

func main() {
	//fmt.Println(snapshotLineRegex.MatchString("dpool/ww[email protected]_frequent-2020-08-04-1830\t0B\t-\t201M\t-"))
	input := bufio.NewScanner(os.Stdin)
	for input.Scan() {
		if snapshotLineRegex.MatchString(input.Text()) {
			fmt.Println(snapshotLineRegex.FindStringSubmatch(input.Text()))
			fmt.Println(snapshotLineRegex.SubexpNames())
		} else {
			fmt.Printf("%s\t%s\n", input.Text(), "Is not a snapshot.")
		}
	}
	if err := input.Err(); err != nil {
		fmt.Fprintln(os.Stderr, "reading Standard Input:", err)
	}
}

Recognizing a snapshot made by zfs-auto-snapshot.