Get rsync to generate a patch file instead of copying across files?

Question

I'm copying lots of files that have changed from one server to another using rsync. I know I can use the -n option to do a dry run, so I can see what files have been changed. However is it possible to get rsync to print a diff of the file contents that's changed? I'd like to see what's happening before doing a copy? Something I can save to a file and the apply with diff(1) later?

Answer 1

There might be a better way, but this might work, albeit not that efficiently:

 rsync -vrn / dest:/ > ~/file_list

Then edit test to remove the stats, then:

while read file; do
    diff $file <(ssh dest "cat $file")
done < ~/edited_file_list

Another Option:
You might also consider mounting the file system with something like sshfs/fuse, and then just using diff.

Answer 2

rsync can't do this natively, but if there's a possibility of using unison you can produce diff style format from that.

Answer 3

It's not possible natively because rsync only cares about binary differences between files.

You might be able to script it, using rsync's output. But it would be hackish.

I do believe it's natively possible with Unison though.

Answer 4

The rsync algorithm works by comparing binary chunks of the file. Such binary diff is not meant to be printable. There is a command called rdiff that uses the rsync algorithm to generate a binary diff, but I don't think it'd be useful for what you describe, it is commonly used to implement incremental backups.

Answer 5

Why not just use something like diff (for text files) or xdelta (for binary files) to generate the diffs? Why do you need to specifically get something out of rsync?