On Wednesday 09 June 2010 11:13 AM, Patrick O'Callaghan wrote: > On Wed, 2010-06-09 at 00:39 -0430, Patrick O'Callaghan wrote: >> On Tue, 2010-06-08 at 21:55 -0500, Robert Nichols wrote: >>> There is no way other than linear search to find a file in a tar >>> archive, so tar always has to read** from the beginning of the archive >>> until it comes to a file you want. >> >> IIRC for uncompressed tarballs this is not strictly the case. The layout >> is basically metadata-file-metadata-file-... so it's possible to seek >> over intermediate files in strides (as the metadata includes the file >> size). For compressed tarballs of course this won't work, which is what >> I was trying to say. >> >>> Even after it has extracted everything you >>> asked for, tar will continue to the end of the archive looking for a >>> possible later version of one of the files you wanted, appended with a >>> --concatenate operation after the original archive was created. >> >> A good point which I hadn't considered. > > On further reflexion and a close reading of "info tar", we find the > following: > > `--occurrence[=NUMBER]' > This option can be used in conjunction with one of the subcommands > `--delete', `--diff', `--extract' or `--list' when a list of files > is given either on the command line or via `-T' option. > > This option instructs `tar' to process only the NUMBERth > occurrence of each named file. NUMBER defaults to 1, so > > tar -x -f archive.tar --occurrence filename > > will extract the first occurrence of the member `filename' from > `archive.tar' and will terminate without scanning to the end of > the archive. > > So in case the under discussion (i.e. when there's no possibility of an > updated version of the target appearing later in the tarball), the best > approach would be: > > tar xf tarball.tar.gz --ocurrence target > > thus avoiding the unnecessary processing of the rest of the tarball. > This discussion has been very enlightening. Thank you all. :) > poc > -- Suvayu Open source is the future. It sets us free. -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines
