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I'm trying to copy extended attributes from one file to another using the OSX "xattr" utility. The background is that we are building a backup tool and the files/structure must retain all attributes, ACLs, etc... Everything is working fine except large attributes like resource forks. Small attributes work fine using method below. Attempting this on OS X 10.7.5 Here is what I am doing:

First I identify the attributes on a file using "ls -l@". Result below:

-rwxrwxrwx@ 1 testuser  staff        0  3 Jan  2011 File
        com.apple.FinderInfo         32 
        com.apple.ResourceFork   237246

Now I export the attribute (com.apple.ResourceFork is the one causing issues):

xattr -px com.apple.ResourceFork File > attribfile

I now want to apply this attribute to the copy of the file on another mac using this command:

xattr -wx com.apple.ResourceFork "`cat attribfile`" File

This results in:

-bash: /usr/bin/xattr: Argument list too long

I think I know why it is happening... the resource fork data is way too long to fit in an argument. I have not established the threshold at which it starts to break but I suspect it has to do with ARG_MAX. xargs doesn't help here since it is not several smaller arguments, but one very large one.

So multiple questions:

  1. Is there a way to make xattr accept this large value? Somehow pipe it in via standard input? man page does not show it, but I am not an expert and maybe there is some creative way to do it
  2. Can anyone tell me the proper way to apply a large extended attribute using stock command line tools?
  3. if there is no stock command line tools, any recommendations for 3rd party tools?
hippietrail
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Chris
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  • This could be getting a little involved, but it might not be impossible to reverse-engineer `xattr` and write your own simple replacement which accepts a file of attributes as its input. If you're lucky, there's a single system call with a binding in a convenient scripting language - Perl one-liner? – tripleee Nov 24 '12 at 07:52
  • We're looking at this option. Looks like the tool is MIT license, so its commercial friendly. – Chris Nov 26 '12 at 18:44

2 Answers2

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I don't know of a way to do it with xattr, but there's an old filesystem trick you can use. Note: this is basically obsolete, but still works in 10.8.2; I make no promises about 10.8.3 etc. If the attribfile is in hex format, use this:

xxd -r -p attribfile >File/..namedfork/rsrc

If the attribfile is raw, use cat instead of xxd -r -p. If the attribute is something other than the resource fork, ... I have no idea.

Gordon Davisson
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  • hmmm, I tried exporting the resource forks that way and it was failing in 10.7+. Never tried setting it in that way. I'll give it a try. – Chris Nov 26 '12 at 18:45
  • Well it seems this does work, which solves the problem of resource forks! Thanks! – Chris Nov 26 '12 at 19:45
  • You could also do without the intermediate temporary file: `xattr -p -x com.apple.ResourceFork src | xxd -p -r - > dst/..namedfork/rsrc` – dardo82 Mar 06 '17 at 09:09
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The accepted answer did not work for me, so I continued and found another solution, which I post here in case other people need it.

My problem was copying vlc-2.1.4 to the /Applications folder. It kept saying:

The Finder can’t complete the operation because some data in “VLC” can’t be read or written.
(Error code -36)

And If I tried using a cp in the terminal i was getting the error indicated in this thread.

So what I did was to execute the following commands in the console (summarizing I tar the VLC and untar it in its destination, so ... it works as a cp):

cd /Volumes/vlc-2.1.4/
tar cf /Applications/vlc.tar  VLC.app
cd /Applications/
tar xf vlc.tar 
rm vlc.tar

I hope this will be useful for others with the same problem.

Daniel
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