docker: pass arguments to entrypoint

Question

If I have a super-dumb dockerfile, like this:

FROM ubuntu:latest ENTRYPOINT echo

Is it possible to pass arguments to the ENTRYPOINT, so that it will print whatever argument I pass? I tried docker build -t test . && docker run test foo but I just got an empty line.

I would recommend a combination of arguments and/or environment variables, as this SO answer outlines. You can specify default values if you like. Your ENTRYPOINT line should allow you to make use of an env var. — Eric McCormick
– Eric McCormick, Commented Jan 30, 2018 at 16:11
Is it possible to directly do the thing I'm asking about, or do I need to use a different solution? — ewok
– ewok, Commented Jan 30, 2018 at 16:12
If you can't edit the Dockerfile, you may wish to build a new Dockerfile off of the original one; assuming it's build specific. Otherwise you next best option may be to override the entrypoint during your docker run, such as docker run --entrypoint="<your new entrypoint>". Here's the documentation from Docker. — Eric McCormick
– Eric McCormick, Commented Jan 30, 2018 at 16:15

Mike Doe · Accepted Answer · 2018-01-30 16:43:03Z

You can extend the image and fix the entrypoint:

FROM user_name/image_name ENTRYPOINT ["echo"]

Or override the entrypoint:

docker run --entrypoint=echo user_name/image_name Hello World

Either way you don't need to be the owner of the Dockerfile you mention as long as you have access to the image.

I don't own the dockerfile. I'm trying to find a way to do it from the command line
Either extend the image or override the entrypoint via arguments of docker run then.

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