Running different CircleCI workflows based on environment variables created in a shell script

.circleci slash config.yml

version: 2.1

setup: true

orbs:
  continuation: circleci/continuation@0.1.2

jobs:
  determine-workflow:
    machine: true
    steps:
      - checkout
      - run:
          name: Generate parameters for main job
          shell: /usr/bin/env bash -eo pipefail
          command: |
            env
            export COMMIT_MESSAGES="$(git log stage.. --pretty=format:%B)";

            if [[ "$CIRCLE_TAG" =~ ^v[0-9.]+$ ]]; then
              WORKFLOW='prod'
            elif [[ "$CIRCLE_BRANCH" =~ ^stage ]]; then
              WORKFLOW='stage'
            elif [[ "$COMMIT_MESSAGES" =~ deploy.demo ]]; then
              WORKFLOW='demo'
            else
              WORKFLOW='dev'
            fi

            cat \<<- EOF > /home/circleci/main_parameters.json
              {
                "workflow": "$WORKFLOW"
              }
            EOF

            cat /home/circleci/main_parameters.json

      - continuation/continue:
          configuration_path: .circleci/main.yml
          parameters: /home/circleci/main_parameters.json

workflows:
  version: 2

  setup:
    jobs:
      - determine-workflow

.circleci slash main.yml

version: 2.1

setup: false

parameters:
  workflow:
    type: enum
    enum:
      - prod
      - stage
      - demo
      - dev
    default: dev

jobs:
  # ...
 
workflows:
  version: 2

  stage:
    when:
      equal: [stage, << pipeline.parameters.workflow >>]
    jobs: # ...
    
  prod:
    when:
      equal: [prod, << pipeline.parameters.workflow >>]
    jobs: # ...

  dev:
    when:
      or:
        - equal: [dev, << pipeline.parameters.workflow >>]
        - equal: [demo, << pipeline.parameters.workflow >>]
    jobs: # ...
    

  demo:
    when:
      equal: [demo, << pipeline.parameters.workflow >>]
    jobs: # ...