Rebuild Nixos with ZFS snapshot

nixos-rebuild-snapshot.sh

#!/usr/bin/env bash
# Rebuild NixOS.  Snapshots system before rebuilds that are not dry-run, 
# dry-activate, or rollback.  Expects one required argument to nixos-rebuild:
# 'switch', 'boot', 'test', 'build', 
# 'build-vm', 'build-vm-with-bootloader' 
# 'dry-rebuild', 'dry-activate'
# optional arguments begin with --.  Ex: --upgrade, --upgrade-all, --rollback, etc.

#error handling on
set -e

pprint () {
    local cyan="\e[96m"
    local default="\e[39m"
    # ISO8601 timestamp + ms
    local timestamp
    #timestamp=$(date +%FT%T.%3NZ)
	timestamp=$(date +%Y%m%d-%T-%Z)
    echo -e "${cyan}${timestamp} $1${default}" 1>&2
}

argv="$@"

#snapshot before every nixos-rebuild, but not dry runs or rollbacks
if [[ "$@" =~ 'dry' || "$@" =~ 'rollback' ]]
then
	pprint "Dry run or rollback, skipping ZFS snapshot."
else
	pprint "nixos-rebuild $@ requested, creating zfs snapshot -r rpool@pre-rebuild-snap-$timestamp ... ";
	zfs snapshot -r rpool@pre-rebuild-snap-$(date +%Y%m%d-%T-%Z);
	sleep 5
fi

pprint "Starting nixos-rebuild -v --show-trace $@ ... ";
sleep 5;
nixos-rebuild -v --show-trace $argv