Clearing inherited variables in System.cmd

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Passing env: [] to System.cmd/3 does not clear the child environment.

System.put_env("VENDOR_TOKEN", "development")

System.cmd("sh", ["-c", ~s(printf %s "$VENDOR_TOKEN")], env: [])
#=> {"development", 0}

System.cmd("sh", ["-c", ~s(printf %s "$VENDOR_TOKEN")],
  env: [{"VENDOR_TOKEN", nil}]
)
#=> {"", 0}

The child inherits its parent environment. :env changes only the keys you provide, so an empty list leaves it alone.

Use nil for a token or other value that must not reach a subprocess. Otherwise, a local credential can make a test or external command succeed by accident.

System.cmd/3 documentation

Clearing inherited variables in System.cmd

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