3

I would like to skip a large gzip file when I extract a tar file, but everytime tar starts to gunzip it to look inside it seems.

Even when I just try to peek inside tar seems to start gunzipping it, for example:

tar -tvf my.tar.gz --exclude="huge_mysql_file.gz"

Any tips how to skip entirely that file? I see gzip running when tar gets to that gz file.

Improve this question
5
  • 2
    why do you think that tar is gunzipping the file? Commented Sep 30, 2012 at 7:27
  • Try gzip -dc my.tar.gz | tar tf -. Commented Sep 30, 2012 at 8:04
  • It always gets stuck at a large gz file, and when I look at top in another shell window I can see gzip running next to tar. Commented Sep 30, 2012 at 9:16
  • I don't really understand you problem here, but it seems that inside that .tar.gz are other .gz files? If that's the case, then the archive is wrong to begin with. a .tar.gz file, is a gziped tar-file, which contains a collection of uncompressed files. Everything else is pretty much done by an idiot. Commented Sep 30, 2012 at 12:56
  • 1
    As others have pointed out, tar has to read .tar.gz files sequentially, so it can't find out what's after "huge_mysql_file.gz" without reading it in to get to the next file in the archive. If you need to view the contents of a .tar.gz file frequently, you can always create a text file containing the files list. e.g. tar tvzf my.tar.gz > my.tar.gz.list. you can then read that .list file with less or grep it etc. Commented Sep 30, 2012 at 22:43

1 Answer 1

Reset to default
7

my.tar.gz is a gzipped tar file. tar ist short for 'tape archive'. So the file my.tar.gz has to be unzipped by gzip -d before the tar file can be read. There is no random access to the content of a gzip file. I do not really know the gzip file format but at least there is no option for gzip to do this. The 'gzip -d' started by tar to unzip the my.tar.gz file is the gzip you can see. tar does not decompress the file huge_mysql_file.gz but it has to read (and ignore) the file huge_mysql_file.gz because this is provided by the pipe to gunzip.

if the tar file is not gzipped and you list its content like in

tar -tvf my.tar --exclude="huge_mysql_file.gz"

only the header of huge_mysql_file.gz in the archive must be read to know its size. Then tar can skip the file without reading it and continue on the following file.

Improve this answer
3
  • Note that tar cannot do sequential access in this case because the archive is read from a pipe (from gzip), but for a tar in a regular file (uncompressed), it will not read the full content and will skip to the start of each file header in that archive (for -t to display the content) Commented Sep 30, 2012 at 21:50
  • thx to @sch: I will check this and adjust my answer as soon as possible Commented Oct 1, 2012 at 6:08
  • thx again @sch: I rewrote the post and hope now there are no more errors Commented Oct 7, 2012 at 9:11

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.