Docker run ENTRYPOINT does not replace environment variable

Question

I have an entry point as shown here

ENTRYPOINT /usr/bin/java ... /usr/path/$FILE

I am trying to pass an environment variable while starting container

-e FILE=myfile.txt

However this value does not seem to be replaced. Java throws an exception that /usr/path is a directory . If I hard code the entrypoint with a file name in the dockerfile, it works perfectly fine.

ENTRYPOINT /usr/bin/java ... /usr/path/myfile.txt

It confirms $FILE is not replaced.

How to fix this?

NOTE:

Interestingly docker-compose works perfectly fine!!

environment:
  - FILE=myfile.txt

Answer 1

In order to ensure that the shell form of ENTRYPOINT, that you correctly are using, does substitute the environment variable $FILE, add an exec:

ENTRYPOINT exec /usr/bin/java ... "/usr/path/$FILE"

Then check that your docker run -e FILE=xxx yourImage does work.

That supposes that your Dockefile includes an ENV FILE aDefaultFile directive, in order for docker run -e to work.