I currently have two Dockerfiles that are identical except for some ENV vars at the beginning that have different values. I want to combine them into one Dockerfile and select the ENV vars depending on one build-arg / ARG instead.
I tried something like this with $target being either WIN or UNIX:
FROM alpine
ARG target
ARG VAR1_WIN=Value4Win
ARG VAR1_UNIX=Value4Unix
ARG VAR1=VAR1_$target
ARG VAR1=${!VAR1}
RUN echo $VAR1
But it throws an error: failed to process "${!VAR1}": missing ':' in substitution I tried a lot but I'm unable to double expand $VAR1. How do I do this correctly? Thx.
For the conditional syntax, there is a pattern you can use with a multi-stage build:
# ARG defined before the first FROM can be used in FROM lines
ARG target
# first base image for WIN target
FROM alpine as base-WIN
# switching to ENV since ARG doesn't pass through to the next stage
ENV VAR1=Value4Win
# second base image for UNIX target
FROM alpine as base-UNIX
ENV VAR1=Value4Unix
# select one of the above images based on the value of target
FROM base-${target} as release
RUN echo $VAR1
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