function deleteRows() {
  var sheet = SpreadsheetApp.getActiveSheet();
  var rows = sheet.getDataRange();
  var numRows = rows.getNumRows();
  var values = rows.getValues();

  var rowsDeleted = 0;
  for (var i = 0; i <= numRows - 1; i++) {
    var row = values[i];
    if (row[0] == 'delete' || row[0] == '') { // This searches all cells in columns A (change to row[1] for columns B and so on) and deletes row if cell is empty or has value 'delete'.
      sheet.deleteRow((parseInt(i)+1) - rowsDeleted);
      rowsDeleted++;
    }
  }
};