How to extend environment variables in github actions with existing ones? - github

Question

A step in a job requires the setting of an environment variable. is something like the code example below possible to achieve with github actions?
Example:
- name: Do Something
env:
NEW_VAR: $EXISTING_VAR/subdir
run: |
echo $NEW_VAR
I know, that i can directly use the environment variable, but it would be nice to construct new env vars by concatenating old ones.
There is also ${{ env.EXISTING_VAR }}, but it looks like that this expression is not evaluated.

Answer 1

Update 2022
The syntax has changed: ::set-env has been deprecated and is replaced with environment files. This means that you can set the new env variable within run in one step and use it in a subsequent step. The syntax would be:
...
- name: Set env variable
run: |
echo "NEW_VAR=${{ env.EXISTING_VAR }}/subdir/${{ env.OTHER_EXISTING_VAR }}" >> $GITHUB_ENV
- name: Use env variable
run: |
echo ${{ env.NEW_VAR }}
...
One caveat is that I was unable to set and use a new environment variable within the same step. Here is a non-working example of what I mean
...
- name: Set env variable
run: |
echo "VAR_FROM_THE_SAME_STEP=${{ env.EXISTING_VAR }}" >> $GITHUB_ENV
echo "NEW_VAR=${{ env.EXISTING_VAR }}/subdir/${{ env.VAR_FROM_THE_SAME_STEP }}" >> $GITHUB_ENV
...
Resolving ${{ env.VAR_FROM_THE_SAME_STEP }} will not work in this case, you would need to do it in a subsequent step, which is of course no big deal in most cases.

Answer 2

There is another way to set env vars.
Try something like that:
- name: Set env to qa
run: |
echo "::set-env name=ENVIRONMENT::qa"
Although this works for me too:
ECS_DOCKER_COMPOSE: "docker-compose-$ENVIRONMENT.yml"
I guess that GitHub actions not work with "/".
Have you tried without slash?