Is there a script/system to check Ubuntu/Debian sources for updates?

Solution 1:

Subscribe to debian-announce. No, really, you don't want to automate version upgrades, as by definition, things might break.

Solution 2:

Is sudo apt-get update; sudo apt-get upgrade what you're looking for?

Look at section 2.4 of this intro: http://newbiedoc.sourceforge.net/system/apt-get-intro.html

Solution 3:

You tagged you're question as Ubuntu and Debian which is a bit confusing. Your comment to rescdsk's answer seems to indicate you're really looking for an answer for Debian.

However here's a solution for Ubuntu I'm not sure if it will work for Debian or not.

Install update-manager-core if it's not already on the system then you can see if there's a new release using do-release-upgrade -c