Re: [Bug-tar] make your tar archive even more anonymous

[Denis Excoffier]

On Wed, Jul 04, 2012 at 11:47:17AM -0700, Tim Kientzle wrote:
>> On Jul 4, 2012, at 7:01 AM, Denis Excoffier wrote:
>> > 
>> > When tar (e.g. tar-1.26) creates an archive of a directory, the
>> > ordering of files (as shown by "ls -f") is preserved in the archive.
>> > 
>> > I would like an option to make this ordering constant (e.g. alphanumeric),
>> > in order that two directories that compare equal (with "diff -r") would
>> > produce the same archive (provided of course that appropriate --mtime,
>> > --owner, --group and --mode options are also set to the same values).
>> 
>> Does this satisfy your requirement?
>> 
>> find dir | sort | tar cf output.tar -I -
>> 
>> The option you propose can have unpleasant implications
>> for tar's memory requirements.  Sorting each directory
>> requires first reading all the items in that directory
>> into memory.
>> 
>> Tim
>>
Yes, this is ok very often (you mean -T instead of -I)
but i have sometimes more than one single folder, and using a
temporary file seems mandatory, something like:

(cd dir1; find . -print | sort > /tmp/1)
(cd dir2; find . -print | sort > /tmp/2)
tar cf output.tar -C dir1 -T /tmp/1 -C dir2 -T /tmp/2
rm /tmp/1 /tmp/2

which is a little bit more tricky than
tar cf output.tar --sort-directories -C dir1 . -C dir2 .

I understand that in the most general case, the memory requirements
might be huge (or use temporary files like 'sort', or use 'sort'
itself). But it has to be taken into account that someone who stores,
say, 10000 files/subdirs in a single directory has probably the
necessary amount of memory to perform 'ls' (with default arguments) on
this directory, which also sorts the output.

For tar, --no-sort-directories would definitely be the default.

Regards,

Denis Excoffier.