Fix outdated syntax rule about handling of quotes in Compose .env files

[antoineco]

Proposed changes

Since Compose 1.26.0, the following information doesn't seem to be true anymore:

• There is no special handling of quotation marks. This means that they are part of the VAL.

Surrounding quotes (single or double) are effectively removed from the value, like in a shell.

Proof:

# .env
MY_VAL='some_value'

# docker-compose.yml
version: '3.7'

services:

  env-test:
    image: alpine
    environment:
      MY_VAL: ${MY_VAL:-}
    entrypoint:
      - sleep
      - '3600'
    init: true

With either Compose 1.29.2 or Compose 2.2.3:

$ docker-compose config
services:
  env-test:
    entrypoint:
    - sleep
    - '3600'
    environment:
      MY_VAL: some_value
    image: alpine
    init: true
version: '3.7'

After executing docker-compose up with either Compose 1.29.2 or Compose 2.2.3:

$ docker-compose exec env-test printenv MY_VAL
some_value

Related:

• Inconsistent env var parsing from docker-compose.yml compose#2854
• Add python-dotenv to delegate .env file processing compose#7150

cc. @ulyssessouza, maybe you can validate my assumption that the docs are wrong since you worked on the aforementioned issue a while ago?

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Related issues (optional)

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[usha-mandya]

@ulyssessouza Could you PTAL?

[docker-robott]

Thanks for the pull request. We'd like to make our product docs better, but haven’t been able to review all the suggestions.
As our docs have also diverged, we do not have the bandwidth to review and rebase old pull requests.

If the updates are still relevant, review our contribution guidelines and rebase your pull request against the latest version of the docs, then mark it as fresh with a /remove-lifecycle stale comment.
If not, this pull request will be closed in 30 days. This helps our maintainers focus on the active pull requests.

Prevent pull requests from auto-closing with a /lifecycle frozen comment.

/lifecycle stale

[antoineco]

/remove-lifecycle stale

[antoineco]

Superseded by #15759