Update headless raspberry pi using a script

update.sh

#!/bin/bash
# Update script for headless pi
# Add these options to the end of cmdline.txt file
# systemd.run=/boot/firmware/update.sh systemd.run_success_action=reboot systemd.unit=kernel-command-line.target

set -euo pipefail

# Remove options from cmdline for normal reboot
cleanup() {
  exit_code=$?
  sed -i 's/systemd.*//g' /boot/firmware/cmdline.txt
  exit $exit_code
}

trap cleanup EXIT

CONN_NAME=foo
SSID=bar
PASSWORD=foobar

umask 177
cat <<EOF >/etc/NetworkManager/system-connections/$CONN_NAME.nmconnection
[connection]
id=$CONN_NAME
uuid=$(uuid)
type=wifi
[wifi]
mode=infrastructure
ssid=$SSID
hidden=false
[ipv4]
method=auto
[ipv6]
addr-gen-mode=default
method=auto
[proxy]
[wifi-security]
key-mgmt=wpa-psk
psk=$PASSWORD
EOF