How to get environment variables in docker cron?

Question

Docker

Building cron container:
Dockerfile

FROM ubuntu:latest

RUN apt-get update && apt-get -y install cron

# Add crontab file in the cron directory
ADD crontab /etc/cron.d/hello-cron

# Give execution rights on the cron job
RUN chmod 0644 /etc/cron.d/hello-cron

# Apply cron job
RUN crontab /etc/cron.d/hello-cron

CMD ["cron", "-f"]

crontab

* * * * * echo "TEST ${TEST}" > /proc/1/fd/1 2>/proc/1/fd/2

I run to check the visibility of a variable

$ docker build . -t cron
$ docker run --env TEST=xxx cron env | grep TEST
TEST=xxx

I run cron

$ docker run --env TEST=xxx cron
TEST

How to make a script run from cron see the passed variables?

Answer 1

Cron always runs commands with an empty environment, docker has nothing to do with it. There are a couple of solutions here:
https://serverfault.com/questions/337631/crontab-e...