Not an answer but an extension of the question.

If I want to copy the contents of say File1 to a new File2 while only being able to have one file open at a time in SD.

It seems that I can open File1 and read to a buffer until say a line end, and then close File1, open File2 and write to File2. Close File2 and reopen File1.

Then I have a problem, having reopened File1 I need to read from where I had got to when I last closed it. Read the next until say line end, close File1, reopen File2 as append and write to File2.

The append means that File 2 gradually accumulates the information so no problem but I am unclear as to how in File1 I return to the last read location.

Do I need to loop through the file each time I open it for the number of, until line end, reads previously done?