How to pass ARG value to ENTRYPOINT?

Like Blake Mitchell sais, you cannot use ARG in ENTRYPOINT. However you can use your ARG as a value for ENV, that way you can use it with ENTRYPOINT:

Dockerfile

ARG my_arg
ENV my_env_var=$my_arg

ENTRYPOINT echo $my_env_var

and run:

docker build --build-arg "my_arg=foo" ...