docker how to break COPY into multiple lines

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The Dockerfile causes the error.

Error response from daemon: dockerfile parse error line 4: COPY requires at least two arguments, but only one was provided. Destination could not be determined.

Is it because COPY command cannot split into multiple lines? What is the way to split into multiple lines then? There are examples for RUN command using \ && but not sure of COPY.

Dockerfile

FROM python:3.7-slim
WORKDIR /app

COPY [
    "requirements.txt",
    "serving/main.py",
    "."
]
RUN pip install --upgrade -r requirements.txt

ENTRYPOINT ["python"]
CMD ["/app/main.py"]

I can put into one line but it is not readable.

COPY [ "requirements.txt", "serving/main.py", "training/simple_linear_regr_utils.py", "training/simple_linear_regr.py", "."]
docker
1 Answers

In a Dockerfile, \ is the line continuation character. It can be used to split any directive across multiple physical lines. && has nothing to do with Dockerfile syntax; that's shell syntax is only relevant in RUN lines (which are executed by the shell).

So you can write:

COPY requirements.txt \
     serving/main.py \
     .

But! That probably won't do what you want, in that you'll end up with a directory that looks like:

/app
├── main.py
└── requirements.txt

That is, it copies everything into the same directory without preserving the directory hierarchy (but so does your COPY [ ... ] version).

user_1473560
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