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def main : IO Unit := do
  -- Read input immediately without waiting for newline
  _ ← IO.Process.run {
    cmd := "stty"
    args := #["-F", "/dev/tty", "cbreak", "min", "1"],
  }
  -- Hide user input
  _ ← IO.Process.run {
    cmd := "stty"
    args := #["-F", "/dev/tty", "-echo"],
  }
  let stdin ← IO.getStdin
  while true do
    let a ← stdin.read 1
    match String.fromUTF8? a with
    | some str => IO.println s!"Hello {str}"
    | none => return