podman/docs/source/markdown/options/env-merge.md

####> This option file is used in: ####> podman create, run ####> If you edit this file, make sure your changes ####> are applicable to all of those.

--env-merge=env

Preprocess default environment variables for the containers. For example if image contains environment variable hello=world user can preprocess it using --env-merge hello=${hello}-some so new value will be hello=world-some.