MinecraftUpdater is a Python script that will automatically update your Minecraft server.jar when placed in the same directory and run (e.g. through cron). It is based on eclair4151's project of the same name. Below follows the original description.
# MinecraftUpdater
This is a python package to automate the updating of your server. Its so annoying to try and download the jar,
ftp it over, stop the server, back up your world, etc. This automates alll that. just git clone this in the root of
your server so there is an extra folder. Then run python update.py in the new folder. it will check if you have the
latest version. If not if will download the latest jar, then using screen it will announce to the server that it will
shutdown and give a 30 seconds countdown before stopping the server. it will then backup your world into a new folder
when it updates incase something goes wrong. then update the server jar and start the server back up in screen so its in the background.