As part of transitioning from using an old desktop to a new desktop (while both are still active), I found the 'rsync' command to be very useful. Here is the options I ended up using to accomplish my goal of copying over (old) files from the old machine to the new without wiping out any new files on the new machine:
rsync -avzuhP --log-file=/destination/dir/rsync_log.txt -e ssh remoteuser@remotehost:/source/dir /destination/dir/
Here's what the options do:
-a archive
-v verbose
-z compress
-u update <= Do Not Overwrite the Modified Files at the Destination
-h human-readable
-P progress bar/partial transfers
Note that these options are turned on in '-a' archive mode:
-r, --recursive recurse into directories
-l, --links copy symlinks as symlinks
-p, --perms preserve permissions
-t, --times preserve times
-g, --group preserve group
-o, --owner preserve owner (super-user only)
-D same as --devices --specials
