env-file

Learn to load variables from a file with --env-file.

--env-file

Instead of writing many variables one by one with -e, they are collected in a file. Each line has the form NAME=value; lines starting with # are comments. Values aren't quoted (the quotes become part of the value):

# app.env
DB_HOST=db
DB_PORT=5432
DB_USER=app
LOG_LEVEL=info

docker run -d --env-file app.env api:1.0

Order and secrecy

--env-file and -e can be used together; if the same variable is in both, -e wins. Env files containing secret values aren't put under version control; a sample file without values is shared instead:

docker run -d --env-file app.env -e LOG_LEVEL=debug api:1.0

# .gitignore
app.env
# sample put in the repo: app.env.ornek
DB_PASSWORD=

Exercise An env file

Write the contents of the app.env file: DB_HOST=db, DB_PORT=5432, LOG_LEVEL=info (each on its own line). On the last line, write the command starting a container named api from api:1.0 in the background using this file.

Show example solution

# app.env
DB_HOST=db
DB_PORT=5432
LOG_LEVEL=info

docker run -d --name api --env-file app.env api:1.0

Test yourself

If LOG_LEVEL="info" is written in app.env, what is the value in the container?
- It errors
- "info" (with the quotes)
- info
- Empty
Show answer

"info" (with the quotes) — docker run --env-file doesn't strip quotes; Compose's .env reading does.

Read the variables from a file.

docker run -d ____ app.env api:1.0

Show answer

docker run -d --env-file app.env api:1.0

Match.

NAME=value

One line
# comment

Ignored
conflict with -e

-e wins
app.env.ornek

Shared sample

Next lesson: The WORKDIR instruction

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