Variable substitution using real environment variable fallbacks

[nick-jones]

#54 introduced a change that meant substitution of variables from the real environment (i.e. not that derived from .env itself) was possible.

It looks like #58 removed this behaviour, in particular the deletion of os.LookupEnv - https://github.com/joho/godotenv/pull/58/files#diff-224f281bd0a4cfe0e7dcb394e8c7a585L299. Unfortunately it isn't clear from the PR if that was intended. Any chance someone can clarify?

[andrewmclagan]

Also needing this functionality back..

[fabriciojs]

@nick-jones @andrewmclagan well 1 year later, I had the same need in my project.

I created #102.

For now I am using https://github.com/fireworkweb/godotenv (my fork) where I returned the behaviour.

Just registering this here in case someone stumbles upon this issue and then can check the latest on this.

[nick-jones]

@fabriciojs 👍 there is also #72 and #88. Unfortunately no word from @joho on this.

[evandam]

Hey @fabriciojs we're looking for similar functionality, but where it is able to read environment variables from os.Getenv if the variable in the file has not been defined, like https://github.com/fireproofsocks/dotenvy/blob/main/docs/dotenv-file-format.md#interpolation-aka-variable-substitution.

Is this something that you would be able to update in your fork? (or @joho)

Thanks!

[luisdavim]

#135 and #149 also relate to this.

This is clearly an issue users care about, with so many issues and PRs open regarding it.

@joho any specific reason for this not to be addressed?

[Envek]

Also made #227 as all other pull requests got stale due to parser rewrite in version 1.5.