How to pass bind port as a param ?

[Baptistemontan]

I'm deploying my app with docker on heroku and the doc says I need to bind to port $PORT, so in the dockerfile I have

ENV LEPTOS_OUTPUT_NAME="my-app"
ENV LEPTOS_SITE_ROOT="site"
ENV LEPTOS_SITE_PKG_DIR="pkg"
ENV LEPTOS_SITE_ADDR="0.0.0.0:${PORT}"

but from what I understand $PORT is not static and is not known when the docker is image built, it is set as en environnement variable when the container is launched.

Is there a way to have something like

ENTRYPOINT ["/my-app", "--port", "$PORT"]

[Baptistemontan]

for now I have a work around where I have a start.sh script

#!bin/sh

export LEPTOS_SITE_ADDR="0.0.0.0:$PORT"

./${LEPTOS_OUTPUT_NAME}

and do

ENTRYPOINT ["/start.sh"]

in the Dockerfile