system-helpers/usr/local/bin/check_updates

#!/usr/bin/env bash

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

Sends out update notifications. Please see man check_updates.
EOF
  )
  echo "$USAGE"
}

set -e

# 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
}

apply_defaults() {
  [[ -z ${CHECK_UPDATES_UPDATES_CMD} ]] && CHECK_UPDATES_UPDATES_CMD="/usr/bin/checkupdates"
  [[ -z ${CHECK_UPDATES_UPDATES_AMOUNT_CMD} ]] && CHECK_UPDATES_UPDATES_AMOUNT_CMD="/usr/bin/checkupdates | wc -l"
}

check_required() {
  if [[ -z ${CHECK_UPDATES_UPDATES_CMD} ]]; then
    echo "CHECK_UPDATES_UPDATES_CMD is required"
    exit 1
  fi
  if [[ -z ${CHECK_UPDATES_UPDATES_AMOUNT_CMD} ]]; then
    echo "CHECK_UPDATES_UPDATES_AMOUNT_CMD is required"
    exit 1
  fi
  if [[ -z ${CHECK_UPDATES_MAIL_ADDRESS} ]]; then
    echo "CHECK_UPDATES_MAIL_ADDRESS is required"
    exit 1
  fi

  type hostname &> /dev/null || { echo "Requiring 'hostname' but it's not installed"; exit 1; }
  type mailx &> /dev/null || { echo "Requiring 'mailx' but it's not installed"; exit 1; }
}

source_config "$1" "$HOME/.check_updates.conf" "/etc/check_updates.conf"
apply_defaults
check_required

HOSTNAME=$(hostname)
CHECK_UPDATES_UPDATES=$(eval "${CHECK_UPDATES_UPDATES_CMD}")
CHECK_UPDATES_UPDATES_AMOUNT=$(eval "${CHECK_UPDATES_UPDATES_AMOUNT_CMD}")

if [[ "$CHECK_UPDATES_UPDATES_AMOUNT" -gt "0" ]]; then
  SUBJECT="[updates ${HOSTNAME}]"
  MESSAGE=$(
    cat <<EOF
There are ${CHECK_UPDATES_UPDATES_AMOUNT} updates available on ${HOSTNAME}.

${CHECK_UPDATES_UPDATES};
EOF
  )
  echo "$MESSAGE" | mailx -Ssendwait -s "$SUBJECT" "$CHECK_UPDATES_MAIL_ADDRESS"
fi