Why do I get files like ._foo in my tarball on OS X?

Question

When I tar certain files in OS X:

tar cvf foo.tar foo

It produces an extra file ._foo in the tarball:

./._foo
foo

which only shows up if I extract it on a non-Mac operating system. But ._foo doesn't exist on my file system! What's going on? How can I get rid of it?

Answer 1

It's a product of extended file attributes. The file foo has an extended attribute, which you can see with ls -l:

$ ls -l
...
-rw-r--r--@ 1 beder  staff     760 Oct 26 19:12 foo

The @ sign indicates that it has an extended attribute. To see what it is:

$ xattr foo
com.apple.TextEncoding

tar recognizes the extended attribute and creates ._foo in the archive, which is then reconstructed when it's unpacked. So how to get rid of them? It's actually pretty annoying. For one file, it's easy:

$ xattr -d "com.apple.TextEncoding" foo
$ ls -l
...
-rw-r--r--  1 beder  staff     760 Oct 26 19:12 foo

Presto! But for many files, it's more difficult. I used the following script to get rid of them, but it's pretty slow:

# /usr/bin/bash

dir=$1

rmvattr() {
    cd "$1"
    echo "Entering $1"
    for d in *
    do
        if [ -d "$d" ]; then
            (rmvattr "$d")
        else
            enc=`xattr $d`
        if [$enc != ""]; then
                xattr -d $enc $d
            fi
        fi
    done
}

(rmvattr $dir)

Unfortunately, there is no option for tar to ignore extended attributes (on Linux, it appears --no-xattrs works, but this doesn't exist on my version of tar). One option is to copy everything, and use the option cp -X, which ignores extended attributes. Another option, which I found from a couple threads, including here is to set

export COPY_EXTENDED_ATTRIBUTES_DISABLE=true

on Tiger, or

export COPYFILE_DISABLE=true

on Leopard. Then tar (and I think everything else) will ignore all extended attributes.

Answer 2

The period character, ".", is used on the Mac platform as a hidden file indicator. On Windows, it is the "$" character. Anyways, the ._foo file probably holds some OS X specific information and I would recommend against deleting it. On other systems you will have to ignore it, or someone here might be able to provide you with a script that will hide files and folders that begin with a ".".

Answer 3

Here's a python script for removing those files. Should work in any popular OS.

Not thoroughly tested, use at your own risk!

import os
import os.path

def dot_clean(folder):
    files = os.listdir(folder)
    for file in files:
        full_name = folder + "/" + file
        if os.path.isdir(full_name):
            dot_clean(full_name)
        elif file.startswith("._"):
            os.remove(full_name)

dot_clean('.')            

Answer 4

The ._ files are resource forks as mentioned in other answers. However, there's a better way to get rid of them when using tar:

export COPYFILE_DISABLE=true
tar cvf foo.tar foo

There's also a dot_clean utility for cleaning up these files (I think it's usually used for external storage).