Bash script for automated shutting down if there are no active sessions

autohalt.sh

#!/bin/bash

# Copy script to `/etc/cron.hourly/autohalt` (*without extension*).
# Log and pid files will be placed in root directory.

DELAY=${1:-30} # minutes
LOG=${2:-"autohalt.log"}
PID=${2:-"autohalt.pid"}

function log {
  echo "[$$][$(date)] $1" >> $LOG
}

function loop {
  local STEP=0
  while [ $STEP -lt $DELAY ]; do
    sleep 1m

    local SESSIONS=$(w -h | wc -l)
    if [ $SESSIONS -eq 0 ]; then
      log "No active sessions found on step $STEP, sleeping..."
      STEP=$((STEP + 1))
    else
      log "$SESSIONS active session(s) found, sleeping..."
      STEP=0
    fi
  done
}

function main {
  log "Starting..."

  if [ -f $PID ]; then
    log "Pid file found, exiting..."
    exit 0
  else
    echo $$ > $PID
  fi

  loop

  log "No active sessions, shutting down..."
  rm -f $PID
  halt
}

main &