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.

[silverwind]

Is there a fork of this module with env substitution added back? According to #182, the autor sees the module as "complete", I'm not sure on their stance regarding this issue.

Edit: I forked, applied #227 and tagged it as github.com/silverwind/godotenv@v1.0.1, works perfectly.

[Envek]

But also according to #182:

Exceptions will be made to:

• …
• maintain compatibility with env file formats of other mainstream "dotenv" libraries, primarily the OG Ruby dotenv and the Node.js dotenv

And OG Ruby dotenv has variable substitution using real environment variables, so we can hope that @joho will finally notice #227 one day.

[silverwind]

But also according to #182:

Exceptions will be made to:

• …
• maintain compatibility with env file formats of other mainstream "dotenv" libraries, primarily the OG Ruby dotenv and the Node.js dotenv

And OG Ruby dotenv has variable substitution using real environment variables, so we can hope that @joho will finally notice #227 one day.

Yes, expansion from environment also is a feature in JS dotenv, specifically with the dotenv-expand module that enables expansion:

https://github.com/motdotla/dotenv-expand/blob/ff7e2efd0d9925c7da82c167ae77d22a6c76e878/tests/main.js#L50-L64

[joho]

I'll give #227 a review and merge if I'm confident on backwards compatibility

[joho]

I've done a pre-release at https://github.com/joho/godotenv/releases/tag/v1.6.0-pre.1

I've set something in my calendar to do the full release on nov 15th (AU time) to give time for bug reports to come in and remediate if needed.