This is a very simple CLI script for updating an Atom feed.
I had to hack together something as I couldn't find a simple CLI based atom feed generator. It does no XML parsing or anything fancy, so it may break your existing feed if you use it ;-)
# Create a feed if it doesn't exist yet
./feedy.sh test.atom
# You have to manually edit the feed and enter your Author name and host
# Add a new entry to your feed
./feedy.sh test.atom 'Cool new feed entry'
Host the feed on a http server like Nginx or Apache