How to get the md5sum of a file on Amazon's S3

Question

If I have existing files on Amazon\'s S3, what\'s the easiest way to get their md5sum without having to download the files?

Thanks

Answer 1

ETag does not seem to be MD5 for multipart uploads (as per Gael Fraiteur's comment). In these cases it contains a suffix of minus and a number. However, even the bit before the minus does not seem to be the MD5, even though it is the same length as an MD5. Possibly the suffix is the number of parts uploaded?