Docker shell script not parameterizing as expected

Question

I have the following run.sh script:

#!/bin/bash
if [[ "$1" = build ]]
then
    python -m flask run --host=0.0.0.0
else
    echo "$1"
fi

And the following Dockerfile definition:

FROM python:3
COPY "app.py" /
COPY "requirements.txt" /
COPY "run.sh" /
RUN ["pip", "install", "-r", "requirements.txt"]
RUN ["chmod", "+x", "/run.sh"]
ENV FLASK_APP app.py
EXPOSE 5000
ENTRYPOINT /run.sh
CMD build

./run.sh foo prints out foo , but docker build . -t test; docker run test docker build . -t test; docker run test docker build . -t test; docker run test prints an empty line. How come?

Answer 1

Use the json/exec syntax for your CMD and ENTRYPOINT lines. Otherwise docker will wrap the commands with a shell:

ENTRYPOINT ["/run.sh"]
CMD ["build"]

See the table in this documentation for more details on how the two syntaxes interact.