Linux Rsync – Compare Two Directories and Copy Differences to a Third Directory

diff()directorylinuxrsync

Running ubuntu 12.04, I want to compare 2 directories, say folder1/ and folder2/ and copy any files that are different to folder3/. There are also nested files, so matching subdirectories should be copied as well

Is there a single command that would help me? I can get the full list of changed files running:

rsync -rcnC --out-format="%f" folder1/ folder2/

But rsync doesn't seem to have the ability to "export" these files on a different target directory. Can I pipe the list to cp or some other program, so that the files are copied, while the directories are created as well? For example, I tried 

rsync -rcnC --out-format="%f" folder1/ folder2/ | xargs cp -t folder3/

but that wouldn't preserve directories as well, it would simply copy all files inside folder3/

Best Answer

Use --compare-dest.

From the man page:

--compare-dest=DIR - This option instructs rsync to use DIR on the destination machine as an additional hierarchy to compare destination files against doing transfers (if the files are missing in the destination directory). If a file is found in DIR that is identical to the sender's file, the file will NOT be transferred to the destination directory. This is useful for creating a sparse backup of just files that have changed from an earlier backup.

first check your syntax with --dry-run

rsync -aHxv --progress --dry-run --compare-dest=folder2/ folder1/ folder3/

Then once you're satisfied with the output:

rsync -aHxv --progress  --compare-dest=folder2/ folder1/ folder3/

this link has a good explanation of --compare-dest scope.

Related Topic