如何在 bamboo specs 部署文件中检索变量

Question

我有以下 deploy.yaml 文件

deployment:
  name: a deploy
  source-plan: dp

environments:
  - first.env

first.env:
  requirements:
    - name: excel_exec
  variables:
    - env_name: first.env
  tasks:
     - artifact-download:
         - destination: end1
           name: some.${env_name}.out
         - destination: end2
           name: another_end

${env_name}

虽然总是空的。我错过了什么？