$BUILDKITE_ENV_FILE is not documented

[nhooyr]

https://github.com/buildkite-plugins/docker-buildkite-plugin/blob/7340a5f7cfc8ffe9af8d1813e110a66d5771998c/hooks/command#L208

Its used by the docker plugin to propagate the env through correctly but doesn't seem to be documented.

[lox]

Correct, it's not documented, which means it's undocumented and you shouldn't depend on it. Here be dragons!

[nhooyr]

Pretty much anyone who uses Docker to run builds with a custom infrastructure will want it. Otherwise I can't use my pipeline's env variables in my command steps. It should become a supported feature.

[lox]

Indeed, it's a tricky problem to solve, as Docker's env file format is basically broken. Some context at buildkite/agent#682.

[nhooyr]

Confused what you mean. Docker's env file format being broken is independent of this issue.

[lox]

Kinda. My point is just that you can't simply jam BUILDKITE_ENV_FILE into docker's --env-file. Let us know how you go with it and we can potentially include some documentation in future.

[nhooyr]

I'm confused still. I'm aware of that and use the same technique the docker plugin does to do it properly. My concern is this feature is very useful but not documented.

[nhooyr]

See https://github.com/buildkite-plugins/docker-buildkite-plugin/blob/7340a5f7cfc8ffe9af8d1813e110a66d5771998c/hooks/command#L209-L213

[lox]

Noted!

[nhooyr]

@lox so why are you hesitant to document this?

[lox]

I'm not really, if you'd submitted a PR instead of an issue I'd probably just have merged it!

[harrietgrace]

BUILDKITE_ENV_FILE is being added as part of #361. I'll leave this open until it's merged.