set the slack status as away on screen lock and back to active on screen unlock

update-slack-status-on-lock-events

#/bin/bash

TOKEN='put your token here. Get a new from https://api.slack.com/docs/oauth-test-tokens'

dbus-monitor --session type='signal',interface='com.canonical.Unity.Session' | while true
do
  read x
  if echo "$x" | grep -q Locked; then
    echo "set yourself away at $(date)"
    curl -X GET -H "Cache-Control: no-cache" "https://slack.com/api/users.setPresence?token=$TOKEN&presence=away"
  elif echo "$x" | grep -q Unlocked; then
    echo "set yourself active at $(date)"
    curl -X GET -H "Cache-Control: no-cache" "https://slack.com/api/users.setPresence?token=$TOKEN&presence=auto"
  fi
done

Getting dbus-monitor: command not found. How to make it work for Mac-based systems? I really appreciate any help you can provide.

You can't - dbus is Linux specific. You would need to work out how you can detect presence in Mac.