sending mispelled words in a file

Hello,


I would like to use aspell to check a text file in a non-interactive way, aspell
should only output in a separate file the list of mispelled words of the input
file.


In fact I would like aspell to do the same as :
spell myfile.txt > mistakes.txt


But I cannot find any option to do that. I believe I have missed one option in
the documentation, but I cannot find which one.

How could I do that with aspell ?