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.
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
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