You can use the rsync command to synchronize folders.
rsync -a source --delete destination
The source and destination represents the paths to your folders.
rsync -a /mnt/sda1/ --delete /home/user/some_dir
-a will archive all folders and subdirectories
--delete will synchronize folders
The /mnt/sda1 is a usb stick, it will have the recent updated files. Rsync will make a duplicate copy of
/mnt/sda1 to /home/user/some_dir
Use the --delete with caution! This will delete files
from the destination path not found in the source path.
In other words, files updated or deleted from the source will be applied equally to the destination.
You can do the same thing without the --delete option. This will keep the files on both sides updated, but nothing is deleted.