Hi,
We have a CLI in the works, announcement post here: Release Announcement · Render CLI v0.1.0
But also, you could use the API (with a helpful tool called jq), e.g.
$ curl --request GET \
--url 'https://api.render.com/v1/services/SERVICE_ID/env-vars?limit=20' \
--header 'accept: application/json' \
--header 'authorization: Bearer API_KEY' \
| jq -r '.[] | (.envVar.key + ": " + .envVar.value)'
Alan