Evaluate bash expression in Dockerfile

Question

I'm trying read application version from a file VERSION such that echo -n 1.0.0 > VERSION, and store the version number in an environment variable, lets say, VERSION. My Dockerfile

FROM debian
WORKDIR /app
COPY VERSION .
ENV VERSION $(cat VERSION)
# I'd like to use the version number in later steps like
RUN apt update && apt install -y curl
RUN curl path/to/executable-${VERSION}

env | grep VERSION returns:

VERSION=$(cat VERSION)

I want

VERSION=1.0.0

you can not set value for ENV using subshell as it key pair only, but you can try suggested answer. or if you still want from file then try something like RUN curl path/to/executable-$(cat VERSION) — Adiii
– Adiii, Commented Nov 27, 2019 at 18:36

ShayK · Accepted Answer · 2019-11-27 22:04:20Z

2

ENV does not interpolate variables.

How about this:

FROM debian
WORKDIR /app
COPY VERSION version-file
RUN echo "export VERSION=$(cat version-file)" >> /root/.bashrc
RUN apt update && apt install -y curl
RUN curl path/to/executable-${VERSION}

This uses a RUN step to add an export command to .bashrc file. the export command adds the VERSION env var.

answered Nov 27, 2019 at 22:04

ShayK

4393 silver badges6 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Moazzem Hossen Over a year ago

looks like an easy workaround for my case. build-arg seems a better option though

alex067 · Accepted Answer · 2019-11-27 18:30:16Z

1

You can provide the version number as a build argument

FROM debian
ARG VERSION
WORKDIR /app
ENV VERSION=$VERSION
# I'd like to use the version number in later steps like
RUN apt update && apt install -y curl
RUN curl path/to/executable-${VERSION}

Then you can build it with:

docker build --build-arg $VERSION .

answered Nov 27, 2019 at 18:30

alex067

3,3211 gold badge14 silver badges19 bronze badges

3 Comments

Moazzem Hossen Over a year ago

Thanks for the answer. CI tool builds the image. I'll see if I can pass as argument.

alex067 Over a year ago

which CI tool are you using?

Moazzem Hossen Over a year ago

concourse registry-image resource. github.com/vito/oci-build-task. It takes BUILD_ARG

Collectives™ on Stack Overflow

Evaluate bash expression in Dockerfile

2 Answers 2

1 Comment

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related