Script input data run commands based off it

Question

Not sure where to begin I only know basic text processing.

I am trying to create a script that will search for zfs snapshots based off a VM name (given as a command parametet) and then select the newest snapshot and finally transfer it to another server.

For example I will run

script.sh 2839

Which will first run

zfs list -t snapshot | grep "vm-2839"

find the following files, and select the newest one based off the date

zfs/backups/vm-2839-disk-0@ZAP_home1_2023-01-20T21:53:29p0000--1d      193M      -     11.9G  -
zfs/backups/vm-2839-disk-0@ZAP_home1_2023-01-22T11:54:19p0000--1d     18.2M      -     11.9G  -
zfs/backups/vm-2839-disk-0@ZAP_home1_2023-01-22T16:08:20p0000--1d        0B      -     11.9G  -

It should then finally send that file to an external server

zfs send zfs/backups/vm-2839-disk-0@ZAP_home1_2023-01-22T16:08:20p0000--1d | ssh [email protected] "zfs receive zfs/vm-2839-disk-0"

Answer 1

Luckily, the date format you're using is numerically sortable.

So the approach to this is

• Tell zfs list to not output data you don't care about
• Tell zfs list to sort according to the date of creation
• take the first line of output and roll with it

So, I don't have zfs set up on the machine I'm sitting in front of right now, so I'm just going of the official documentation – as you should have!

#!/bin/bash

machine=$1 # save the first passed argument in the variable "machine"

zfs list -o name -s creation -t snapshot | grep "vm-${machine}" |tail -n1 | xargs zfs send | ssh [email protected] "zfs receive zfs/vm-${machine}-disk-0"

#         ^------------------------------ specify the field(s) to display;
#                ^                        "name" is the first mentioned on the
#                |                        man page.
#                |
#                \----------------------- specify which field to sort by. As
#                                         linked to, zfsprops man page tells
#                                         that "creation" is the time the
#                                         snapshot was created
#
#                                                             ^---- pipe to "tail", which
#                                                                   ^---- keeps the last 1 line(s)
#
#                                                                        ^---- pipe to xargs, which
#                                                                              takes the input and
#                                                                              appends it as argument
#                                                                              to the passed command
#                                                                              "zfs send"
#          
#                                                                                      ^---- pipe to
#                                                                                            your ssh
#                                                                                            as before