I would suggest to use rysnc command :
rsync (stands for remote synchronization) is an open source tool for data transfers between Unix systems.
rsync synchronizes directories – makes one directory look (contain the same files and subdirectories) exactly like another one. by comparing them as per specified criteria (file size, creation/modification date or checksum) .
How to use rsync :
sudo rsync -az /pathof folder A /pathof folder B
sudo rsync -az /pathof folder B /pathof folder A
-a archive mode (implies recursive, copy symlinks as symlinks, preserve owner, modification times, group, owner, special and device files)
-z compresses the data
I would Suggest also to use watch command which will repeat rsync every interval of time , or use cron .
For more info about watch command : Here
Reference : Here