Docker ENTRYPOINT behaving differently from --entrypoint option

user_10153573 0
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My Dockerfile:

FROM my-image-base

COPY src src

RUN chmod +x src/script.sh

ENTRYPOINT ['/src/script.sh']

After successful build:

docker run created_image

/bin/sh: [/src/script.sh]: No such file or directory


docker run --entrypoint /src/script.sh created_image

script runs successfully

I feel like I'm overwriting the default ENTRYPOINT with the same thing but it behaves differently. Am I misunderstanding something?

docker
1 Answers

No, it's not the same thing, because your ENTRYPOINT is invalid.

ENTRYPOINT has two forms:

  • The shell command form:

    ENTRYPOINT command param1 param2

  • and the exec form:

    ENTRYPOINT ["executable", "param1", "param2"]

Which of the two forms are you using here? If you answer "the second", you have been subtly led astray, because you have single-quotes ' there instead of double-quotes "!

As specified in the docs:

Note: The exec form is parsed as a JSON array, which means that you must use double-quotes (") around words not single-quotes (').

So, you actually have the first form, the shell command form.

Docker will pass your "command" to the shell, like this:

/bin/sh -c "['/src/script.sh']"

Due to the way quotes work when parsing shell command lines, this ends up being equivalent to typing [/src/script.sh] into your shell. The shell then rightfully complains that that's not a valid command.

user_18710330
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