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tar operations, ‘--create’ (‘-c’),
‘--list’ (‘-t’) and ‘--extract’ (‘--get’,
‘-x’), are currently presented and described in the tutorial
chapter of this manual. This section provides some complementary notes
for these operations.
Creating an empty archive would have some kind of elegance. One can
initialize an empty archive and later use ‘--append’
(‘-r’) for adding all members. Some applications would not
welcome making an exception in the way of adding the first archive
member. On the other hand, many people reported that it is
dangerously too easy for
tar to destroy a magnetic tape with
an empty archive(9). The two most common errors are:
extract, when the intent was to extract the full contents of an archive. This error is likely: keys c and x are right next to each other on the QWERTY keyboard. Instead of being unpacked, the archive then gets wholly destroyed. When users speak about exploding an archive, they usually mean something else :-).
file, when the intent was to create an archive with a single file in it. This error is likely because a tired user can easily add the f key to the cluster of option letters, by the mere force of habit, without realizing the full consequence of doing so. The usual consequence is that the single file, which was meant to be saved, is rather destroyed.
So, recognizing the likelihood and the catastrophic nature of these
tar now takes some distance from elegance, and
cowardly refuses to create an archive when ‘--create’ option is
given, there are no arguments besides options, and
‘--files-from’ (‘-T’) option is not used. To get
around the cautiousness of GNU
tar and nevertheless create an
archive with nothing in it, one may still use, as the value for the
‘--files-from’ option, a file with no names in it, as shown in
the following commands:
tar --create --file=empty-archive.tar --files-from=/dev/null tar -cf empty-archive.tar -T /dev/null
A socket is stored, within a GNU
tar archive, as a pipe.
tar now shows dates as ‘1996-08-30’,
while it used to show them as ‘Aug 30 1996’. Preferably,
people should get used to ISO 8601 dates. Local American dates should
be made available again with full date localization support, once
ready. In the meantime, programs not being localizable for dates
should prefer international dates, that’s really the way to go.
Look up http://www.cl.cam.ac.uk/~mgk25/iso-time.html if you are curious, it contains a detailed explanation of the ISO 8601 standard.
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