from the rsync man page
-a, --archive
This is equivalent to -rlptgoD. It is a quick way of saying you
want recursion and want to preserve almost everything (with -H
being a notable omission). The only exception to the above
equivalence is when --files-from is specified, in which case -r
is not implied.
Note that -a does not preserve hardlinks, because finding multi-
ply-linked files is expensive. You must separately specify -H.
-u, --update
This forces rsync to skip any files which exist on the destina-
tion and have a modified time that is newer than the source
file. (If an existing destination file has a modify time equal
to the source file’s, it will be updated if the sizes are dif-
ferent.)
In the current implementation of --update, a difference of file
format between the sender and receiver is always considered to
be important enough for an update, no matter what date is on the
objects. In other words, if the source has a directory or a
symlink where the destination has a file, the transfer would
occur regardless of the timestamps. This might change in the
future (feel free to comment on this on the mailing list if you
have an opinion).
-v, --verbose
This option increases the amount of information you are given
during the transfer. By default, rsync works silently. A single
-v will give you information about what files are being trans-
ferred and a brief summary at the end. Two -v flags will give
you information on what files are being skipped and slightly
more information at the end. More than two -v flags should only
be used if you are debugging rsync.
Note that the names of the transferred files that are output are
done using a default --out-format of "%n%L", which tells you
just the name of the file and, if the item is a link, where it
points. At the single -v level of verbosity, this does not men-
tion when a file gets its attributes changed. If you ask for an
itemized list of changed attributes (either --itemize-changes or
adding "%i" to the --out-format setting), the output (on the
client) increases to mention all items that are changed in any
way. See the --out-format option for more details.
-E, --extended-attributes
Apple specific option to copy extended attributes, resource
forks, and ACLs. Requires at least Mac OS X 10.4 or suitably
patched rsync.