// Define value binder function unixTimestampToDate($value) { return date('Y-m-d', $value); } // Set value binder for cell A1 PHPExcel_Cell::setValueBinder(new PHPExcel_Cell_AdvancedValueBinder(), PHPExcel_Cell::COLUMN_STRING . '1', 'unixTimestampToDate'); // Set value for cell A1 $objPHPExcel->getActiveSheet()->setCellValue('A1', 1546300800); // Output cell value echo $objPHPExcel->getActiveSheet()->getCell('A1')->getValue(); // Output: 2019-01-01In this example, we define a value binder function `unixTimestampToDate` that takes a Unix timestamp value and returns a formatted date string. We then set this value binder function to be used for cell A1 using `PHPExcel_Cell::setValueBinder`. We set the value of cell A1 to a Unix timestamp using `PHPExcel_Worksheet::setCellValue`, and then output the formatted value of the cell using `PHPExcel_Worksheet::getCell`. The package library used in this example is PHPExcel, a library for reading and writing Microsoft Excel files in PHP. However, PHPExcel has been deprecated and replaced by PhpSpreadsheet. Thus, the `PHPExcel_Cell` class and related classes may not be available in newer versions of PhpSpreadsheet.