Sure thing, I'm currently using it in docker as a lightweight way to set config files from environment variables. I'll put together a write up of how/why we are doing that and post the link in reply to this.
Just today I made a suggestion in a Github issue[0] to use sed for a similar use case. There, it was to generate an Amazon ECS task definition file from a CI tool's environment variables. Using this, populating the list of environment variables by looping through the output of env and including anything that matches a given prefix would be a breeze.
This is perfect! Thank you for taking the time to make this. It gave me a much better understanding of what sempl is, how to use it, and what it can be used for.