Rsync will compare the contents of the source directory with the target directory. If it finds a match, it won’t copy the files, if there’s no match, it copies.
If your goal is to have 1:1 copies, you can use the --delete flag to remove extraneous files in the target directory that aren’t in the source directory.
If you use the -a flag, it’ll maintain all of your permissions.
You can literally rsync a linux installation from one machine to another. While the source machine is running. Pretty nuts.
With some pens, you can jam the spring between the button and the silver thing on the bottom right and the white thing next to it. Then jam it into the top of the pen with the ink stick until it sticks.
Then press the button on the top of the pen and the white thing shoots across the room.