check-upgrades.py

#! /usr/bin/env python3

# this script assume that sendmail is working on your system

import socket
from email.mime.text import MIMEText
import subprocess
import re

subprocess.run(['apt', 'update'], stdout=subprocess.DEVNULL, stderr=subprocess.STDOUT)
dry_run_update = subprocess.run(
    ['apt-get', 'upgrade', '--dry-run'],
    stdout=subprocess.PIPE,
    stderr=subprocess.STDOUT
).stdout.decode('utf-8')

dry_run_result = re.search(
    r"^(\d+) upgraded, (\d+) newly installed, (\d+) to remove and (\d+) not upgraded\.$",
    dry_run_update,
    flags=re.MULTILINE
)
to_upgrade = int(dry_run_result.group(1))
to_install = int(dry_run_result.group(2))
if to_upgrade == 0 and to_install == 0:
    exit()  # nothing to upgrade

to_be_upgraded = re.search(
    r"^The following packages will be upgraded:(.*)not upgraded\.$",
    dry_run_update,
    flags=re.DOTALL | re.MULTILINE
).group()


msg = MIMEText("Following is a dry-run of the upgrade:\n" + to_be_upgraded)
msg["From"] = "root@" + socket.getfqdn()
msg["To"] = "[email protected]"
msg["Subject"] = "There are updates to do on " + socket.getfqdn()
subprocess.run(["/usr/sbin/sendmail", "-t", "-oi"], input=msg.as_bytes(unixfrom=True))