My issue is with exporting env variables from within a shell script into action env variables.

I tried using the echo “::set-env…”  from within the shell script without success - I suspect ::set-env does not trigger the action from registering env variables

pseudocode e.g.

calc-version.sh

#!/bin/bash
export VERSION=19.2.5
export FULL_TAG=19.2.5-beta
export SHORT_TAG=beta

build-docker.yml

<snip>
- name: calc version
   run: ./calc-version.sh 

name: build and push myimage

run: |

docker build -t myimage:${{ env. FULL_TAG }} .

docker push myimage:${{ env.FULL_TAG }}

docker tag myimage:${{ env. FULL_TAG }} myimage:${{ env.SHORT_TAG }}

docker push myimage:${{ env.SHORT_TAG }}

You should access your env vars like this

docker build -t myimage:${FULL_TAG} .
docker build -t myimage:$FULL_TAG .

I guess that run command executes as is. So double curly braces isn’t a valid syntax for shell command, at least to access env variable. The two variants above are valid.

I think that the following syntax ${{ env. FULL_TAG }} it’s a way to access variables in the YAML context. For example, pass arguments to actions.

I tried add set-env command in bash scripts calc-version.sh : 

#!/bin/bash
echo "::set-env name=VERSION::19.2.5"

My workflow is : 

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v2
    - name: set output
      id: set
      run: |
   chmod +x calc-version.sh
   ./calc-version.sh

- name: use output
  run: |
    echo $VERSION
    echo ${{env.VERSION }}

Both invoke env variable syntax could work: 

VERSION  and {{env.VERSION }}

echo var.png763×480 10.1 KB

Can you try again? 

Thanks for documenting this. It pointed me in the right direction.
Github has changed the mechanism since then though. Read here how it now works:

Workflow commands for GitHub Actions - GitHub Docs

//docs.github.com/en/actions/reference/workflow-commands-for-github-actions