var fHandle; 

...
function fSave{

  fHandle = file_open_write("test.txt");

  file_str_write(fHandle, "start"); //1......
  
  file_asc_write(fHandle, 13);  // cr
  file_asc_write(fHandle, 10);  // lf

  file_str_write(fHandle, "end"); //2......

  file_asc_write(fHandle, 13);  // cr
  file_asc_write(fHandle, 10);  // lf

  file_close(fHandle);
}