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How can I evaluate and assign default value to ARG in dockerfile?

Basically I want to assign a dynamically calculated default value for ARG in my Dockerfile:

FROM node:20-alpine

ARG RELEASE_TAG=$(git describe --tags --always)

# Other commands...

So, far it doesn’t interpolate the value of $(git describe --tags --always) and simply assigns this value to the RELEASE_TAG variable.

Is there any way I can achieve this?

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2

Answers


  1. 0

    You can use the --build-arg argument with docker build

    export RELEASE_TAG=$(git describe --tags --always)
docker build --build-arg RELEASE_TAG=$RELEASE_TAG -t your_image_name .

    And inside your Dockerfile:

    FROM node:20-alpine

ARG RELEASE_TAG

    That way, RELEASE_TAG will now have the value of git describe --tags --always output.

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  2. 0

    You can achieve the expected effect by putting it in RUN :

    FROM ubuntu

WORKDIR /app

COPY . .

RUN apt-get update && apt-get install -y git
RUN RELEASE_TAG=$(git describe --tags --always) &&
    echo npm run build -- --version=$RELEASE_TAG

CMD sleep inf
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