生成中未拾取环境变量

Dockerfile文件

FROM node:lts-alpine as build-stage
ENV VUE_APP_BACKEND_SERVER=${_VUE_APP_BACKEND_SERVER}
RUN echo "server env is:"
RUN echo $VUE_APP_BACKEND_SERVER
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run gcpbuild

Cloudbuild配置

steps:
  - name: gcr.io/cloud-builders/docker
    args:
      - build
      - '--no-cache'
      - '-t'
      - '$_GCR_HOSTNAME/$PROJECT_ID/$REPO_NAME/$_SERVICE_NAME:$COMMIT_SHA'
      - front
      - '-f'
      - front/Dockerfile
      - '--build-arg=ENV=$_VUE_APP_BACKEND_SERVER'
    id: Build
...
...
options:
  substitutionOption: ALLOW_LOOSE
substitutions:
  _VUE_APP_BACKEND_SERVER: 'https://backend.url'

我还在“高级”部分的替换中设置了变量。然而,在构建过程中 echo 打印一个空白,而该变量在应用程序中不可用。