It's usually a good idea to store your app's environment variables separate from the app itself in a .env file. This allows you to easily have different values for development, staging, and production.
Normally when writing a .env file, you might have an unusual property like an API key that has lots of special characters. Typically you would quote this value to handle that.
# a normal environment variable, surrounded by single quotes
KEY='example bl4h 5tuFF 123@#%= ksjhbfdg'
Your system would know to treat what's inside the single quotes as the value of KEY and make it available to your app.
But Docker doesn't work this way.
Let's say you're passing a .env file into a Docker container via docker-compose.yml. Docker would interpret the quotes around the environment variables as part of the value itself!
For a real world example, here's an environment variable passed to the official WordPress Docker image and the resulting output in the container's wp-config.php file (value is random and not used for anything, obviously):
# environment variable in a .env file
WORDPRESS_DB_PASSWORD='Pr65s$CWv{P3k}4j6]I<j=U5n#keN&$D{{Uhv2@L'
// output to wp-config.php
// notice the escaped \' at the beginning and end
define( 'DB_PASSWORD', '\'Pr65s$CWv{P3k}4j6]I<j=U5n#keN&$D{{Uhv2@L\'');
The database password in wp-config.php would be incorrect because Docker considered the single quotes as part of the key value!
So as weird and wrong as it appears, when using .env files with Docker, don't quote values! The above example done correctly would then look like this:
# environment variable in a .env file
WORDPRESS_DB_PASSWORD=Pr65s$CWv{P3k}4j6]I<j=U5n#keN&$D{{Uhv2@L
// output to wp-config.php
define( 'DB_PASSWORD', 'Pr65s$CWv{P3k}4j6]I<j=U5n#keN&$D{{Uhv2@L');
Top comments (4)
This article is out-of date. At some point (~v1.28), docker-compose switched to using dotenv to parse the environment files. Single and double-quoted strings are parsed specially. single-quoted strings can be multiline. Double-quoted strings can have escapes such as "\n" to produce multi-line values.
The article is not outdated for peoople who use Docker Swarm. Its still behaves incorrectly:
$ docker compose up ... with .env_file
$ docker stack deploy ... with .env_file
So if you're going to use Swarm mode you should... avoid quotes and spaces in JSON values and define them like:
it's not outdate. I've ran into this problem today and I'm using Docker version 20.10.23, with node 18 and typescript. And, it took me too much time to find this post. Thanks OP
It made me realize my docker version was way too old.