Compare & Copy Directories : Bash Script Help

view full story

http://www.unix.com – Beginner/Intermediate shell; comfortable in the command line. I have been looking for a solution to a backup problem. I need to compare Directory 1 to Directory 2 and copy all modified or new files/directories from Directory 1 to Directory 3. I need the directory and file structure to be mirrored on Directory 3. Another way of thinking about the logic is: Dir1 - Dir2 = Dir3. I want Dir3 to be portable between users/machines so I don't think an incremental backup with hardlinks will work. Seems like it should be easy right? I found a scripts that seems like it could do the trick. However, (HowTos)