dehydrated
letsencrypt/acme client implemented as a shell-script
...Other dependencies are cURL, sed, grep, mktemp (all found on almost any system, cURL being the only exception). Please keep in mind that this software and even the acme-protocol are relatively young and may still have some unresolved issues. Feel free to report any issues you find with this script or contribute by submitting a pull request. dehydrated is looking for a config file in a few different places, it will use the first one it can find.