Sorry for this "newbie" question. I found myself the answer :
tarsnap -x -f MyArchive /CompletePath/singlefile
Jean-Louis
> Message du 04/01/13 09:32
> De : "Jean Louis FEREY"
> A : tarsnap-users@tarsnap.com
> Copie à :
> Objet : How to extract a single file from a Tarsnap archive
>
>> Hi,
>
> Is it possible to extract a single file from a Tarsnap archive like with the tar command : tar xvf backup.tar singlefile ?
>
> Best regards.
>
> Jean-Louis