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Amandasaurus
Asked: 2009-09-05 03:02:44 +0800 CST

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

  • 772

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?

rsync diff patch-management

7 Answers

  1. Best Answer

    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.

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  2. For create patch:

    rsync -arv --only-write-batch=patch new/ old/

    For apply it:

    rsync -arv --read-batch=patch dir/

    or use auto-generated script:

    ./patch.sh

    Sources:

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

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  4. 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.

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  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?

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  6. To expand on Kyle's answer, this automates the process. Note that it is totally untested, probably pretty fragile, and may delete your computer and kill your dog.

    #!/bin/bash

REMOTE=${1?Missing Remote Path}
LOCAL=${2?Missing Local Path}

# Trim trailing slash since we'll be adding it as a separator later
REMOTE=${REMOTE%/}
LOCAL=${LOCAL%/}

#Break it down
RHOST=${REMOTE%:*}
RPATH=${REMOTE#*:}

while read FILE; do
    diff -u ${LOCAL}/${FILE} <(ssh $RHOST "cat ${RPATH}/${FILE}")
done < <(rsync -vrn $REMOTE/ $LOCAL/ | sed '1d;/^$/q')
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  7. 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.

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