Cannot get rsync to ignore the git folder and the todo file

There are a few possibilities:

• You can just rsync the .git repository (or even whole repository together with working directory), provided that you don't have any activity in repository during rsyncing (same disclaimer as for using rsync:// protocol).

• You can clone or fetch using deprecated rsync protocol (where repository URL / location looks like this: "rsync://host.xz/path/to/repo.git/"). Note that this protocol is deprecated, because if there is any activity in repository, you can get corrupted clone (or fetch).

  Also, as I have heard, it didn't work correctly in the presence of packed refs since 2007, and nobody noticed till recently. It will (it did) disappear in Git 2.8.

• Or you can create git bundle, rsync it or scp it on other machine, and then clone or fetch from bundle.

There are several ways rsync compares files -- the authoritative source is the rsync algorithm description: https://www.andrew.cmu.edu/course/15-749/READINGS/required/cas/tridgell96.pdf. The wikipedia article on rsync is also very good.

For local files, rsync compares metadata and if it looks like it doesn't need to copy the file because size and timestamp match between source and destination it doesn't look further. If they don't match, it cp's the file. However, what if the metadata do match but files aren't actually the same? Then rsync probably didn't do what you intended.

Files that are the same size may still have changed. One simple example is a text file where you correct a typo -- like changing "teh" to "the". The file size is the same, but the corrected file will have a newer timestamp. --size-only says "don't look at the time; if size matches assume files match", which would be the wrong choice in this case.

On the other hand, suppose you accidentally did a big cp -r A B yesterday, but you forgot to preserve the time stamps, and now you want to do the operation in reverse rsync B A. All those files you cp'ed have yesterday's time stamp, even though they weren't really modified yesterday, and rsync will by default end up copying all those files, and updating the timestamp to yesterday too. --size-only may be your friend in this case (modulo the example above).

--ignore-times says to compare the files regardless of whether the files have the same modify time. Consider the typo example above, but then not only did you correct the typo but you used touch to make the corrected file have the same modify time as the original file -- let's just say you're sneaky that way. Well --ignore-times will do a diff of the files even though the size and time match.