CircleCI2.0ではenvironmentで変数展開ができない ref: https://qiita.com/chaspy/items/488e1cc2595a3f76fb00

file0.txt

version: 2
jobs:
  build:
    docker:
      - image: circleci/ruby
    environment:
      - PATH: /path/to/dir:$PATH

file1.txt

    steps:
      - run:
          command: echo 'export PATH=/path/to/dir:$PATH' >> $BASH_ENV