Cron job to shut down an idle computer

shutdown_idle.sh

#!/bin/sh

# This script, intended to be run as a cron job, checks if there are any logins or recent logins and shuts down if there are none. It is not intended to be portable and was written on a Ubuntu 16.04 machine.

last_login_time=$(grep "systemd-logind" /var/log/auth.log | perl -pe "s/ ip.*//" | tail -1 | date --file=/dev/stdin +%s)

if [ $(($cur_time - $last_login_time)) -ge 3600 ] && [ $(who | wc -l) -eq 0 ]
then
  init 0
else
  echo 'current logins:' > /home/ubuntu/logins
  who >> /home/ubuntu/logins
fi