system-helpers/usr/local/bin/check_updates

#!/usr/bin/env bash

# usage
usage() {
USAGE=$(cat <<EOF
Usage: check_updates [CONFIG_FILE (absolute path)]

If no CONFIG_FILE is given, HOME/.check_updates.conf or /etc/check_updates.conf is used. This fallback option
has to exist or the script will exit.

Configuration can be done in any file and any pre-defined variable can be overwritten.

The following are at least required for the script to work:
- CHECK_UPDATES_MAIL_ADDRESS="" // mail.rc has to be configured

You can copy this script to '/usr/local/bin' and use create a custom CONFIG_FILE as user. Examples can be found in '/usr/share/doc/<scriptname>'.
EOF
)
	echo "$USAGE";
}

set -e;

HOSTNAME=$(hostname)
UPDATES=$(/usr/bin/checkupdates)
UPDATES_AMOUNT=$(/usr/bin/checkupdates|wc -l)
CHECK_UPDATES_MAIL_ADDRESS="";

# check for config file
apply_config() {
  local config=$1;

  if [[ ! -f "$config" ]]; then
      echo "No config file specified";
      echo "";
      usage;
      exit 1;
  fi

  set -a;
  # shellcheck disable=SC1090
  source "$config";
  set +a;
}

source_config() {
  local config=$1;
  local configFallback=$2;
  local configGlobalFallback=$3;

  if [[ -f "$config" ]]; then
    apply_config "$config";
    return;
  fi

  if [[ -f "$configFallback" ]]; then
    apply_config "$configFallback";
    return;
  fi

  if [[ -f "$configGlobalFallback" ]]; then
    apply_config "$configGlobalFallback";
    return;
  fi
}
source_config "$1" "$HOME/.check_updates.conf" "/etc/check_updates.conf"

if [ "$UPDATES_AMOUNT" -gt "0" ]; then
	mailx -s "[updates $HOSTNAME]" "$CHECK_UPDATES_MAIL_ADDRESS" << EOF
There are $UPDATES_AMOUNT updates available on $HOSTNAME.

$UPDATES
EOF
fi