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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=

Practice 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.

Starter code

terminal
# app.env
# buraya yaz

Sample solution

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

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

Expected output

a3b4c5d6e7f8

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 If LOG_LEVEL="info" is written in app.env, what is the value in the container?

  • It errors
  • "info" (with the quotes) Correct answer
  • info
  • Empty

Explanation: docker run --env-file doesn't strip quotes; Compose's .env reading does.

2 Read the variables from a file.

Question 
docker run -d ____ app.env api:1.0
Answer 
docker run -d --env-file app.env api:1.0

Explanation: --env-file loads each line as a variable.

3 Match.

Term Meaning
NAME=value One line
# comment Ignored
conflict with -e -e wins
app.env.ornek Shared sample

All lessons in Beginner

1 What is Docker?

  1. What is Docker?
  2. Containers and virtual machines
  3. Images and containers
  4. Docker architecture
  5. Use cases
  6. Summary - What is Docker

2 Installation and first commands

  1. Installing Docker
  2. docker version
  3. docker info
  4. The hello-world container
  5. Docker Desktop
  6. Summary - Installation

3 First container

  1. docker run basics
  2. Running in the background
  3. docker ps
  4. docker stop and rm
  5. docker logs
  6. Summary - First container

4 Dockerfile basics

  1. What is a Dockerfile?
  2. The FROM instruction
  3. The RUN instruction
  4. COPY and ADD
  5. CMD and ENTRYPOINT
  6. Summary - Dockerfile

5 Build and images

  1. docker build
  2. Tagging images
  3. Build context
  4. Layers and cache
  5. .dockerignore
  6. Summary - Build

6 docker run options

  1. Interactive mode
  2. Naming containers
  3. Restart policy
  4. Working directory
  5. Switching users
  6. Summary - docker run

7 Image management

  1. docker images
  2. docker rmi
  3. docker pull
  4. docker push
  5. docker tag
  6. Summary - Image management

8 Port mapping

  1. The port concept
  2. The -p flag
  3. Multiple ports
  4. Random ports
  5. IP binding
  6. Summary - Port mapping

9 Volumes and data

  1. Data persistence
  2. Named volumes
  3. The -v flag
  4. Bind mounts
  5. Volume management
  6. Summary - Volumes

10 Environment variables

  1. The -e flag
  2. The ENV instruction
  3. The ARG instruction
  4. env-file
  5. The WORKDIR instruction
  6. Summary - Environment

11 Project: docker-compose

  1. Compose design
  2. Service definition
  3. Database service
  4. Volume and network
  5. Putting it together - compose

12 Docker Hub and registry

  1. What is Docker Hub?
  2. docker login
  3. Searching images
  4. Official images
  5. Private registry
  6. Summary - Registry

13 Network basics

  1. Network drivers
  2. docker network ls
  3. Bridge network
  4. Container connectivity
  5. Publishing ports
  6. Summary - Network

14 Beginner final

  1. Challenge - Dockerfile
  2. Challenge - Build and run
  3. Challenge - Volume
  4. Challenge - Compose
  5. Challenge - Beginner project