technology, sound, and design
Rsync is an indispensable open source tool originally co-developed by Andrew Tridgell. It is perhaps most widely used to copy files between remote or local mirrors and/or perform incremental backups of data. I highly recommend rsync considering its speed and availability. However, despite being immediate and practical to use, it is best to proceed cautiously by testing its various command functions on non-essential data first.
Here is a link to the current man page.
Below is an example of a useful command that performs a dry-run (thereby allowing the user to preview the tool's behavior), deletes extraneous files within the destination path, and excludes a single directory from transfer if necessary:
# rsync -avn --delete --exclude 'directory/' /source/path/ /destination/path