docker-compose adding to PATH

Question

I need to add some paths to my PATH in docker-compose.yml

in docker-compose.yml I have tried

app:     ...     environment:         - PATH /code/project 

however that just overwrites the existing PATH - whereas I want to add to the existing PATH

Answer 1

A docker-compose.yml does not offer you any mean to extend an environment variable which would already be set in a Docker image.

The only way I see to do such things is to have a Docker image which expects some environment variable (let's say ADDITONAL_PATH) and extends at run time its own PATH environment variable with it.

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Let's take the following Dockerfile:

FROM busybox ENV PATH /foo:/bar CMD export PATH=$PATH:$ADDITIONAL_PATH; /bin/echo -e "ADDITIONAL_PATH is $ADDITIONAL_PATH\nPATH is $PATH" 

and the following docker-compose.yml file (in the same directory as the Dockerfile):

app:   build: . 

Build the image: docker-compose build

And start a container: docker-compose up, you will get the following output:

app_1 | ADDITIONAL_PATH is

app_1 | PATH is /foo:/bar:

Now change the docker-compose.yml file to:

app:   build: .   environment:     - ADDITIONAL_PATH=/code/project 

And start a container: docker-compose up, you will now get the following output:

app_1 | ADDITIONAL_PATH is /code/project

app_1 | PATH is /foo:/bar:/code/project

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Also note a syntax error in your docker-compose.yml file: there must be an equal sign (=) character between the name of the environment variable and its value.

environment:     - PATH=/code/project 

instead of

environment:     - PATH /code/project 

Answer 2

I know this is an old thread, but I think there are a couple of things that can be clarified.

Through docker-compose file one can only address variables from the host machine, therefore it is NOT possible to extend image's PATH from docker-compose.yml:

app:     ...     environment:         - PATH=/code/project:$PATH 

On the other hand, using RUN or CMD EXPORT directive will not suffice due to EXPORTED variables not persisting through images. Since every Dockerfile directive generates an intermediate image, these values will be reflected in them and not in the main image where you actually need them.

The best option would be to use build option in docker-compose.yml:

  app:     build: . 

and adding ENV option to a Dockerfile:

ENV PATH /path/to/bin/folder:$PATH

This is suggested in issue #684 and I would also suggest looking at an answer: docker ENV vs RUN export.