Per an answer to another question, you can set the undocumented(?) environment variable COPYFILE_DISABLE to prevent several of the system-supplied programs (including tar) from giving special meaning to
._* archive members. In particular, it will prevent them from:
storing extended attribute data (including resource forks) in
._* archive members
(i.e. do not “pollute” archives created on Mac OS X but meant for use on other systems), and
attempting to extract extended attributes or resources from archive members named like
(i.e. do not misinterpret
._* archive members in archives from other systems).
The value you use for the environment variable is not important (it can even be the empty string). Values like
false will not reenable the feature. The only thing that matters is whether the variable is set (you have to “unset” it to reenable the feature).
You can use this variable on individual commands by taking advantage of the ability of Bourne-style shells (sh, ksh, bash, zsh, etc.) to prefix commands with extra environment variables.
COPYFILE_DISABLE=1 tar cf new.tar …
If you run into the problem more often than not, then you might want to set and export this variable in one of your shell’s initialization files.
# turn off special handling of ._* files in tar, etc.
COPYFILE_DISABLE=1; export COPYFILE_DISABLE
When you need to, you can then unset the variable for individual commands.
(unset COPYFILE_DISABLE; tar cf somefile.tar …)
On this Mac OS X 10.6 system, the following commands all seem to know about COPYFILE_DISABLE:
/usr/bin/tar (a symbolic link to
COPYFILE_DISABLE originated in Mac OS X 10.5. If you need to support 10.4, it has COPY_EXTENDED_ATTRIBUTES_DISABLE that works in the same way.