Pass host environment variables to dockerfile

Question

How can I pass a host environment variable (like user and hostname) to a dockerfile?

For example, if my username is taha:

echo $USER
taha

How do I write my Docker file to get the same output?

FROM centos:centos7   
ARG myuser=$USER  
CMD echo $myuser

Possible duplicate of [Get environment variable value in Dockerfile](https://stackoverflow.com/questions/19537645/get-environment-variable-value-in-dockerfile) — callmemath, Aug 01 '17 at 15:07

Serey · Accepted Answer · 2017-08-01T14:38:35.193

I was experiencing the same issue. My solution was to provide the variable inside of a docker-compose.yml because yml supports the use of environment variables.

In my opinion this is the most efficient way for me because I didn't like typing it over and over again in the command line using something like docker run -e myuser=$USER . . .

Declaring ENV myuser=$USER will NOT work, in the container, $myuser will be set to null.

So your docker-compose.yml could look something like this:

version: '3'
services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
    environment:
       - "myuser=${USER}"

and can be run with the short command docker-compose up

To check that the variable has been applied, run docker exec -it container-name printenv to list all variables in the container.

I guess I need to use Docker-compose, I m new to this, I try it and tell if it works, hopefully it does :) — , Aug 01 '17 at 14:39

score 6 · Answer 2 · answered Aug 01 '17 at 14:26

6

When you start your docker container you can pass environment variables using the -e option like so:

docker run -it <image> -e USER=$USER /bin/bash

answered Aug 01 '17 at 14:26

TDk

1,019
6
18

Great, what to do when you ENV var is a path to a very sensitive file in your host machine (don't want to copy the file to the container)? Create a volume to access the file? – hzitoun Dec 11 '19 at 12:03
1

You can simplify that to `docker run -it -e USER /bin/bash` – Josh Coady Dec 12 '19 at 03:01
@hzitoun yes, depending on your situation, mount it for access – Josh Coady Dec 12 '19 at 03:02

icc97 · Answer 3 · 2021-02-11T16:31:04.493

I had a similar use-case where I wanted to be able to specify a version for the image. This has a slight extra requirement that you must specify the ARG before the FROM.

First we specify IMAGE_VERSION in the Dockerfile, as per the question I'm also including a USER arg that we can pass in too:

# give it a default of latest
# declare the ARG before FROM
ARG IMAGE_VERSION=latest
FROM centos:${IMAGE_VERSION}
ARG myuser  
CMD echo $myuser

Then, as from the Docker compose docs on args:

Add build arguments, which are environment variables accessible only during the build process.

You can add these in your docker-compose.yml for example:

version: '3'
services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
      args:
        "myuser=${USER}"
        IMAGE_VERSION

Then as long as you have IMAGE_VERSION set in your environment it will be passed through.

score -4 · Answer 4 · answered Aug 01 '17 at 14:24

-4

you need to use the ENV setting in your dockerfile

ENV myuser=$USER

https://docs.docker.com/engine/reference/builder/#env

answered Aug 01 '17 at 14:24

Derick Bailey

72,004
22
206
219

FROM centos:centos7 ENV myuser=$USER CMD echo $myuser but it doesn't print the username – Aug 01 '17 at 14:41
This won't take the value of $USER from the host machine. – Ankur Bhatia Nov 13 '18 at 13:50

Pass host environment variables to dockerfile

4 Answers4

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