slackMon.sh

#!/bin/bash

DEBUG=1
# Indicator string as seen in dbus messages. Will probably change frequently.
DM_INDICATOR='chrome_app_indicator2_5dc5a4d4fc9f0cfd05f90bfbb2390e06'

function debugEcho {
  if [ "$DEBUG" -eq 1 ] ; then
    echo "$@"
  fi
}

# Force the LED off on startup.
xset -led 3

# Monitor the session dbus for messages indicating that Slack's icon changed.
dbus-monitor "type=method_return" | grep --line-buffered -Eo 'chrome_app_indicator2_[^"]+' | while read indicator ; do
  # If the new icon equals the known DM_INDICATOR icon, turn on the light.
  if [[ "$indicator" == "$DM_INDICATOR" ]] ; then
    debugEcho "[[ \"$indicator\" == \"$DM_INDICATOR\" ]]"
    xset led 3
  # Otherwise, turn it off.
  else
    debugEcho "[[ \"$indicator\" != \"$DM_INDICATOR\" ]]"
    xset -led 3
  fi
done