tasks:
  one:
    python: print('one')
    once: true
  two:
    python: print('two')
    once: true
  three:
    python: print('three')
    once: true
  concat:
    python: |
      import os
      print(os.environ['one'], os.environ['two'], os.environ['_'])
    once: true
  nested:
    multi:
      - python: print('nested')
        once: true
  all:
    multi:
      - task: one
        export: one
      - task: two
        export: two
      - task: three
      - task: concat
      - task: nested