Pass env vars to docker image on build, can be used to pass vars during github actions for building a prod vs dev image.

build-run-image.sh

#!/usr/bin/env bash

docker build --build-arg DETECTED_BUILD='PROD' -t dereckmezquita/hello-world:latest .
docker run dereckmezquita/hello-world:latest
#> YEET

Dockerfile

FROM ubuntu:20.04

WORKDIR /app

ARG DETECTED_BUILD
ENV BUILD=$DETECTED_BUILD

COPY . .

ENTRYPOINT [ "/bin/bash", "yeet.sh" ]

yeet.sh

#!/usr/bin/env bash

echo $BUILD