A way to avoid calling a command with read dotenv variables

[frederikhors]

I think we need a way to avoid to execute a command with loaded environments variables from dotenv file.

Example: I use set dotenv-load in a justfile which will call later a command like npm run build. I need to have envs read in my justfile but not for that command because some of them are being modified a from justfile before it executes that command.

[casey]

Check out #953, which would make variable evaluation lazy, i.e. they would only be evaluated when used. Would that fix the problem?

[frederikhors]

I think these are two different problems. And both are needed. 😄

[casey]

Can you provide an example dotenv file, and example justfile? They should be as simple as possible, just to demonstrate the use-case and issue. I want to make sure I understand the use-case.

[frederikhors]

Let's say I have a .env file like:

THIS_IS_CHANGED_DURING_BUILD="123"

APP_URL="https://a"

and a justfile like:

set dotenv-load

build:
  curl {{APP_URL}}
  command that changes .env file here
  npm run build

The npm run build command is executed with both initial envs but this is not correct because I need it to be executed with the updated (by justfile command) .env.

[casey]

Gotcha. My hunch is that this isn't something that can be supported cleanly at the moment. I think the way to go for this is to implement #945, and then have two different .env files, like .just-env for just and .env for npm.

[frederikhors]

Oh. I do not like it very much.

I think .env file needs to be just one.

Can you think about this syntax instead?

set dotenv-load
  I_NEED_THIS
  AND_THIS_ONE_ONLY

[dionjwa]

Two alternative approaches:

• turn that recipe into a bash script, that way you can set or read the env var directly and export it into the script context
• create another recipe structure:

build:
 curl {{APP_URL}}
 command that changes .env file here
 # This will consume the updated .env
 just _build

_build:
 npm run build

This way it's a bit more explicit that you're re-consuming the changed env vars, otherwise there's some indirection in your commands and env vars.