Change permissions on single file in tar.gz file

Question

I need to change permission on a single file in a tar.gz archive without extracting it, but I was unable to find any way to achieve it either on man pages or by google search.

More detailed scenario:

We start on a Linux machine with three files:

[root@localhost tar-test]# ls -l
total 0
-rw-r--r--. 1 root root 0 Nov 17 14:41 a.txt
-rw-rw-r--. 1 root root 0 Nov 17 14:41 b.txt
-rw-r--r--. 1 root root 0 Nov 17 14:41 c.txt

Then we create tar.gz archive:

tar cvzf test.tar.gz a.txt b.txt c.txt

Then, test.tar.gz is sent to my Windows machine. Now I need to change permissions of a.txt file without extracting the whole archive. I have access to MinGW, but not to a full Linux machine (virtual or physical). I also don't want to extract the whole archive. It can be assumed, that I know both name and location of the file in the archive.

The solution is restricted to command line tools, since I intend to script it later on.

Answer 1

I was just faced with the same question and came up with this using Python:

import os, tarfile


def chmod_in_targz(archivepath:str, files_to_change:list[str], new_mode:int):
    os.rename(archivepath, f"{archivepath}.orig")
    with tarfile.open(f"{archivepath}.orig", "r:gz") as source:
        with tarfile.open(archivepath, "w:gz") as target:
            for entry in source.getmembers():
                if entry.path in files_to_change:
                    entry.mode = new_mode # <-- HERE WE CHANGE THE PERMISSION
                target.addfile(entry, source.extractfile(entry))

    os.remove(f"{archivepath}.orig")


cwd = os.path.dirname(__file__)

chmod_in_targz("test.tar.gz", ["a.txt"], 0o666)

Running this will:

1. rename test.tar.gz to test.tar.gz.orig
2. create a new test.tar.gz based on the content of test.tar.gz.orig but with fixed file permissions
3. delete test.tar.gz.orig