OS X extended attributes



Like most other modern filesystems the HFS filesystem on OS X supports extended attributes and OS X access control lists ACL,
Files on OS X using the systems standard HFS file system consists of parts:
Payload data
The actual data
Extended Attributes
like icons
Finder meta-file
color tags, description

Transfer OS X extended attributes: AppleSingle and AppleDouble formats

The OX on board Unix commands like cp copy the OS X extended attributes when the target system supports it.
For user uses like the tar archiver Apple has developed a format to store the extended attributes in a separate file. AppleSingle' combined both file forks and the related Finder meta-file information into a single file, whereas 'AppleDouble stored them as two separate files.

Commands that work with OS X extended attributes

Unix-ls command

To list extended attributes from the command line specify the @-switch with the Unix Unix-ls command:
 ls -l@ *
 -rw-r--r--@ 1 ckent  staff  225868823 Sep  9  2012 Myfile01.flv
com.apple.FinderInfo 42 com.apple.ResourceFork 41338


The xattr command displays and manipulates extended attributes on OS X.
 xattr -l  MyMovie.flv 
 00000000  00 00 00 00 00 00 00 00 04 08 00 00 00 00 00 00  |................|
 00000010  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  |................|

tar command

The Unix-tar archiver command stores OS X extended attributes in a separate file in AppleDouble format.
 time ( tar cvf -  .  |( cd /Volumes/UserHDA/ahaack/; tar xvf - )) 2> /tmp/kenterr.log

Status: Published Date: 2017/06/05 14:13:06 Revision: 1.1

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