<a id="hello"></a>
## Hello

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Example input:

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```yaml
on: push
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - run: echo ${{ unknown }}
```

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Output:

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```
test.yaml:6:23: undefined variable "unknown". available variables are "env", "github", "inputs", "job", "matrix", "needs", "runner", "secrets", "steps", "strategy", "vars" [expression]
  |
6 |       - run: echo ${{ unknown }}
  |                       ^~~~~~~
```

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[Playground](https://rhysd.github.io/actionlint/#eNokyjEOhSAQRdGeVbzit2yA3XwMCVEzQ5x5sSDs3YxWtzhXpWDQetq1WkmAN/MocFEsh7NSnPn8h71k3oZ9F5DjLGhbV/zmBOUQvQVrPQEAAP//SLkdHQ==)

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This is minimal test case.
