copy/copy.go
func isTTY(w io.Writer) bool {
	if f, ok := w.(*os.File); ok {
		return terminal.IsTerminal(int(f.Fd()))
	}
	return false
}
func isTTY(w io.Writer) bool {
	if f, ok := w.(*os.File); ok {
		return terminal.IsTerminal(int(f.Fd()))
	}
	return false
}
// isTTY returns true if the io.Writer is a file and a tty.