using environment variables in docker-compose mounted files for initializing mysql - mysql

Question

I am having trouble initializing mysql via docker-compose with the use of /docker-entrypoint-initdb.d whenever my initializing scripts requires environment variables.
I have the following docker-compose.yml file.
version: '3'
services:
mysql:
image: mysql
container_name: mysql
restart: always
env_file: .env
environment:
- MYSQL_ROOT_PASSWORD=$MYSQL_ROOT_PASS
- MYSQL_USER=$MYSQL_USER
- MYSQL_PASSWORD=$MYSQL_PASS
- MYSQL_DB=$MYSQL_DB
volumes:
- db-data:/var/lib/mysql
- ./init.sql:/docker-entrypoint-initdb.d/init.sql
ports:
- $MYSQL_PORT:3306
volumes:
db-data:
This is my ./init.sql
CREATE DATABASE IF NOT EXISTS ${MYSQL_DB};
GRANT ALL PRIVILEGES ON ${MYSQL_DB}.* TO '${MYSQL_USER}'#'%';
DELETE FROM mysql.user WHERE User='root' AND Host NOT IN ('localhost', '127.0.0.1', '::1');
When I run docker-compose up, I get an error with my ./init.sql and here's what it says:
mysql | 2021-07-16 14:53:17+00:00 [Note] [Entrypoint]: /usr/local/bin/docker-entrypoint.sh: running /docker-entrypoint-initdb.d/init.sql
mysql | ERROR 1064 (42000) at line 1: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '{MYSQL_DB}' at line 1
Everything works perfectly if I change my ~/init.sql to use hardcoded values like this :
CREATE DATABASE IF NOT EXISTS testingdb;
GRANT ALL PRIVILEGES ON testingdb.* TO 'testinguser'#'%';
DELETE FROM mysql.user WHERE User='root' AND Host NOT IN ('localhost', '127.0.0.1', '::1');
# where testingdb and testinguser is my .env.MYSQL_DB and .env.MYSQL_USER respectively
How do I use environment variables in docker's volume mounted files?

Answer 1

Env variables can be used in .sh file, so you can achieve what you want like this:
Create an init_db.sh file (instead of init_db.sql)
Then in the init_db.sh file:
echo "** Creating default DB and users"
mysql -u root -p$MYSQL_ROOT_PASSWORD --execute \
"CREATE DATABASE IF NOT EXISTS $MYSQL_DB;
GRANT ALL PRIVILEGES ON $MYSQL_DB.* TO '$MYSQL_USER'#'%';
DELETE FROM mysql.user WHERE User='root' AND Host NOT IN ('localhost', '127.0.0.1', '::1');"
echo "** Finished creating default DB and users"