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WesternGun
Asked: 2022-01-01 05:10:39 +0800 CST

GNU tar - update tar file, overwriting the original file in command line(which is possible by drag-and-drop in Archive Manager)

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I want to update a tar file with part of the content modified, by overwriting the original file, in a script.

I tried tar -u, -A and -r, but none does what I want. I also tried with --overwrite.

An easy test:

cd ~
mkdir test
echo foo > test1.txt
mkdir test_dir
cd test_dir
echo bar > test2.txt
cd ../..
tar cvf test.tar test
tar tvf test.tar # check content
echo barbarbar >> test/test_dir/test2.txt
tar rvf test.jar test # or Avf, or uvf, it's the same: modified file does not overwrite the original file in the tar
  • -u --overwrite theoretically will "update", but actually it only appends and does not append the changed file, so I see two test1.txt and one test2.txt there in the tar, with the test2.txt being the old one
  • -A --overwrite theoretically will append, but errors out: tar: test: Read error at byte 0, while reading 1024 bytes: Is a directory tar: Error is not recoverable: exiting now
  • -r --overwrite theoretically will "append", but will only append, and no overwrite, so I see two test1.txt and two test2.txt in the tar.

I thought: OK then tar does not include the possibility of updating the tar in place. But then I remember that this can be achieved easily by drag the new folder to the tar file in Gnome(I think this is handled by "Archive Manager"), so it's at least possible.

How can I overwrite files in tar in command line/script?

command-line

2 Answers

  1. you could create a script that would create another tarball instead of updating the original and then remove the original and rename the new one as the original...

    the way that the "archive manager" app is probably doing this is a bit more advanced and I wouldn't bother trying to emulate that behavior in bash, but that doesn't mean that you shouldn't try...

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  2. I found this paragraph in GNU tar doc, so overwriting is not supported by tar. I will remove the original file from the tar, and append the modified one.

    https://www.gnu.org/software/tar/manual/html_node/how-to-update.html#how-to-update

    4.2.3.1 How to Update an Archive Using ‘--update’

    You must use file name arguments with the ‘--update’ (‘-u’) operation. If you don’t specify any files, tar won’t act on any files and won’t tell you that it didn’t do anything (which may end up confusing you).

    To see the ‘--update’ option at work, create a new file, ‘classical’, in your practice directory, and some extra text to the file ‘blues’, using any text editor. Then invoke tar with the ‘update’ operation and the ‘--verbose’ (‘-v’) option specified, using the names of all the files in the ‘practice’ directory as file name arguments:

    $ tar --update -v -f collection.tar blues folk rock classical
blues
classical
$

    Because we have specified verbose mode, tar prints out the names of the files it is working on, which in this case are the names of the files that needed to be updated. If you run ‘tar --list’ and look at the archive, you will see ‘blues’ and ‘classical’ at its end. There will be a total of two versions of the member ‘blues’; the one at the end will be newer and larger, since you added text before updating it.

    The reason tar does not overwrite the older file when updating it is that writing to the middle of a section of tape is a difficult process. Tapes are not designed to go backward. See section Tapes and Other Archive Media, for more information about tapes.

    EDIT: --delete does not work/is very slow. It seems that delete files from tar is not very feasible, maybe by design. I think I have to extract/remove/repackage, or: https://unix.stackexchange.com/questions/68732/remove-files-from-tar-archive but I don't know how yet.

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