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

update-notifier.sh

#!/usr/bin/env bash

# Requires "pacman-contrib"

# 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 --icon=info "$2 new updates ($1 total)" "Run pacman -Syu to upgrade"
  else
    notify-send --icon=info "$1 updates available" "Run pacman -Syu to upgrade"
  fi
}

# Test for network conection
function online_check {
  for interface in $(ls /sys/class/net/ | grep -v lo);
  do
    online=$(cat /sys/class/net/$interface/carrier)
    if [ "$online" = 1 ]; then
      echo 1
    fi
  done
}

# main app

online=$(online_check)

# Retry in one minute because my laptop is so slow (okay, not that slow) to connect to a wifi network...
if [ "$online" != 1 ]; then
    notify-send --icon=info "Arch Linux package update notifier" "Waiting internet connection... Will retry in one minute."
    sleep 1m
    online=$(online_check)
fi

if [ "$online" != 1 ]; then
  notify-send --icon=error "Arch Linux package update notifier" "Update check failed ! Check your internet connection !"
else
  count=$(update_count)
fi


if [ -f "$cache_file" ] && [ $(cat $cache_file) -ge 0 ]; then
  last_count=$(cat $cache_file)
  if [ $((count+last_count)) = 0 ]; then
    notify-send --icon=info "No package update available..." "How rare is that ?"
  elif [ "$last_count" = "$count" ]; then
    notify $count
  elif [ $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

I added a function to test if a internet connection is up. My laptop takes some time to connect to my wi-fi network and the script would have been launched before the connection is up...

Thanks to the original script, made by logarytm.

Also thanks to the persons who answered on this Stackoverflow thread .