package update notifications for Arch Linux, easily portable to other distros

update-notifier.sh

#!/usr/bin/env bash
# Configuration
cache_file=$HOME/.updates

# function to check updates, must work without root privileges and print
# the number of updates to stdout.
function update_count {
  checkupdates | wc -l; return $?
}

# notification function, called: notify TOTAL [NEW]
function notify {
  if [ $# -eq 2 ]; then
    notify-send "$2 new updates ($1 total)" "Run pacman -Syu to upgrade"
  else
    notify-send "$1 updates" "Run pacman -Syu to upgrade"
  fi
}

count=$(update_count)

if [ -f "$cache_file" ] && [ $(<$cache_file) -ge 0 ]; then
  last_count=$(cat $cache_file)

  if [ $last_count -lt $count ]; then
    notify $count $((count-last_count))
    echo $count > $cache_file
  fi
elif [ $count -ge 0 ]; then
  notify $count
  echo $count > $cache_file
fi