How to run command conditionally in docker compose - bash

Question

I want to run command conditionally in docker-compose
because when someone run this application at first time,
They would have to run migrate command so that they can run django application properly
But If their docker have run migrate, there is no need to run migrate again
So this is the command to check that their docker have run migrate.
if [[ -z $(python3 zeus/manage.py showmigrations | grep '\[ \]')]]; then
echo 'no need to migrate'
else
echo 'need to migate'
fi
This is my docker-compose.
version: '3'
services:
db:
image: postgres
web:
command: >
bash -c "if [[ -z $(python3 zeus/manage.py showmigrations | grep '\[ \]')]]; then
echo 'no need to migrate'
else
echo 'need to migate'
fi && python3 zeus/manage.py runserver 0.0.0.0:8000
"
But Error occurs like this
ERROR: Invalid interpolation format for "build" option in service
"web": "bash -c "if [[ -z $(python3 zeus/manage.py showmigrations | grep '\[ \]')]]; then
echo 'no need to migrate' else echo 'need to migate' fi
&& python3 zeus/manage.py runserver 0.0.0.0:8000""
Any idea?
Edit
This is fine when I run the script of checking migration in normal bash
I think docker-compose can't parse $(python3 manage.py .....) part.

Answer 1

try this :
version: '3'
services:
db:
image: postgres
web:
command: bash -c "if [[ -z $$(python3 zeus/manage.py showmigrations | grep '\\[ \\]') ]]; then
echo 'no need to migrate';
else
echo 'need to migate';
fi && python3 zeus/manage.py runserver 0.0.0.0:8000"
three problems were there , you need to escap the escape charachter \ and add more $ to escape the replacment in compose and one more space before the last ]]

Answer 2

Try to avoid writing complicated scripts in docker-compose.yml, especially if they're for normal parts of your application setup.
A typical pattern is to put this sort of setup in an entrypoint script. That script ends with the shell command exec "$#". In a Docker context, that tells it to replace itself with the command (from a Dockerfile CMD statement or Docker Compose command:). For your example this could look like
#!/bin/sh
if [ -z $(python3 zeus/manage.py showmigrations | grep '\[ \]')]; then
echo 'no need to migrate'
else
echo 'need to migate'
fi
exec "$#"
Then in your Dockerfile, copy this file in and specify it as the ENTRYPOINT; leave your CMD that runs your application unmodified.
COPY entrypoint.sh /app
RUN chmod +x entrypoint.sh
ENTRYPOINT ["/app/entrypoint.sh"]
CMD python3 zeus/manage.py run --host=0.0.0.0:8000
The ENTRYPOINT statement must be the JSON-array form and must not have an explicit sh -c wrapper in it.
If you want to verify that things have gotten set up correctly, you can run
docker-compose run web sh
and you will get a shell at the point that exec "$#" is: after your migrations and other setup have run, but instead of your main server process.