Docker · tool · fg-0268

Variables from the Compose project dotenv file are substituted into the YAML but missing inside the container

printenv inside the container does not list the variable

Verified 2026-10-15 · Confirmed by 0 builders · Trust 50/100

Cause

Compose reads the dotenv file in the project directory only to fill ${VAR} references in the Compose file, and --env-file only changes which file feeds that substitution. Nothing reaches a container unless a service lists it under environment or env_file.

Fix

Reference each variable under environment, or point the service at the file with env_file.

Apply

services:
  api:
    env_file: app.env
    environment:
      DATABASE_URL: ${DATABASE_URL}

Affects: Docker Compose v2, as of October 2026

Sources

• https://docs.docker.com/compose/how-tos/environment-variables/variable-interpolation/

claude mcp add --transport http footgun https://getfootgun.com/api/mcp