How can I use a variable inside a Dockerfile SHELL instruction?

Question

Inside my Dockerfile:

ENV ENV_NAME=dev_env


RUN conda create -n ${ENV_NAME} python=3.8 pip
SHELL ["conda", "run", "-n", "${ENV_NAME}", "/bin/bash", "-c"]

This would cause error which says ${ENV_NAME} is not a virtual environment name. I would like to know how I can use a variable in a SHELL instruction. I tried to follow How can I use a variable inside a Dockerfile CMD? , but it doesn't work in my case.

The SHELL is set and used at build time (for RUN statements in the Dockerfile). So it doesn't make much sense to try to change it at run-time. Can you elaborate on what you're trying to achieve? — Hans Kilian, Apr 24 '22 at 17:16
@HansKilian I'm trying to install Anaconda in Docker image, init it in bash, create a conda virtual environment, and then activate this newly created conda environment (as in the SHELL line). I'm trying to use a env variable ENV_NAME as the conda environment's name. I'm following this: https://tcoil.info/run-conda-from-virtual-environment-inside-docker-and-start-jupyterlab-with-trading-and-ml-libraries/ — CyberPlayerOne, Apr 25 '22 at 06:43
You might be looking for [this answer](https://stackoverflow.com/a/51770027/5362795) but I have not tried it for `SHELL`, it works for `RUN`. — Nagev, Oct 19 '22 at 18:34

score 0 · Answer 1 · answered Apr 24 '22 at 18:00

A Docker image contains a fixed version of some single application. That means you don't need to make every possible thing parametrizable; just pick a name and use it.

# do not set ENV ENV_NAME=...
RUN conda create -n env python=3.8 pip
SHELL ["conda", "run", "-n", "env", "/bin/sh", "-c"]

(If you can use plain pip install without a Conda wrapper, that's even easier: don't create a virtual environment and don't bother changing SHELL, just pip install things into the image's "system" Python.)

How can I use a variable inside a Dockerfile SHELL instruction?

1 Answers1