Access env variables inside docker entrypoint script

Question

I want to pass environment variables in my docker run command and access them in my entrypoint shell script.

This is my super simple Dockerfile for test purposes:

FROM ubuntu:20.04

WORKDIR /

ADD entrypoint.sh .

RUN chmod 755 entrypoint.sh

ENTRYPOINT [ "/entrypoint.sh" ]

And this is the entrypoint.sh:

#!/bin/sh

printf "env var TEST = ${TEST} "

I just build the Dockerfile like this: docker build -t test:1.0 .

And then run it like this: docker run -i test:1.0 -e TEST='Hello world'

Unfortunately the output is not containing the env var.

Answer 1

For the record: Predefining the variables is not the solution.

The order of the args is important, like David Maze said.

# incorrect
docker run -i test:1.0 -e TEST='Hello world'

# correct
docker run -i -e TEST='Hello world' test:1.0 

Answer 2

Something like this will work:

entrypoint.sh

#!/bin/sh
echo $MYVAR

Dockerfile

FROM alpine:3.15.4
WORKDIR /home/app
COPY ./entrypoint.sh .
ENV MYVAR=""
ENTRYPOINT ["/bin/sh", "/home/app/entrypoint.sh"]

And then you can build & run the container while setting the environment variable with:

$ docker build -t test . && docker run -e MYVAR="hello world" test