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Is there a way to modify permissions for a file in a zip without unzipping the file? For clarification, I am not asking to change the contents of the file, but the Unix permissions that are set on one. I have not found an answer for that yet other than extracting and updating the file.

Sir Intellegence-BrainStormexe
  • 237

2 Answers2

5

Yes, sometimes there is. Without going in too deep about the details, a Zip file has a list of entries for each file and then another entry at the end that summarizes them. The entries might or might not have file permissions, it depends on the tool (and its version), filesystem, Zip format, ... But if they do, you can modify them.

The following steps are tested on Debian 10.

Lets create a zip file:

$ echo "This is file 1" > file1.txt
$ chmod 777 file1.txt
$ echo "This is file 2" > file2.txt
$ chmod 555 file2.txt
$ zip files file?.txt

Then list the files and permissions:

$ zipinfo files.zip

Archive:  files.zip
Zip file size: 344 bytes, number of entries: 2
-rwxrwxrwx  3.0 unx       15 tx stor 20-Jun-08 18:35 file1.txt
-r-xr-xr-x  3.0 unx       15 tx stor 20-Jun-08 18:30 file2.txt
2 files, 30 bytes uncompressed, 30 bytes compressed:  0.0%

Now, we could manually iterate through the entries, but there is a program that already does it and prints the result:

$ zipdetail files.zip

That outputs lots of information. You have the offset at the left and the name and contents of each field next to it.

We just want the Ext File Attributes for each file:

$ zipdetails files.zip | egrep "Ext File Attributes|Filename"

001A Filename Length       0009
001E Filename              'file1.txt'
006C Filename Length       0009
0070 Filename              'file2.txt'
00C0 Filename Length       0009
00CA Ext File Attributes   81FF0000
00D2 Filename              'file1.txt'
010F Filename Length       0009
0119 Ext File Attributes   816D0001
0121 Filename              'file2.txt'

Now, let's modify the permissions on file2.txt to make it 777 by writing 0x81FF0000 (the file attributes for file1.txt to offset 0x0119 (decimal 281, the file attributes for file2.txt) taking into account the endianness:

$ printf "\x00\x00\xff\x81" | dd of=files.zip bs=1 seek=281 count=4 conv=notrunc

And list the contents again:

$ zipinfo files.zip
Archive:  files.zip
Zip file size: 344 bytes, number of entries: 2
-rwxrwxrwx  3.0 unx       15 tx stor 20-Jun-08 18:35 file1.txt
-rwxrwxrwx  3.0 unx       15 tx stor 20-Jun-08 18:30 file2.txt
2 files, 30 bytes uncompressed, 30 bytes compressed:  0.0%

Now both files share the same permissions.

If you want to set your own permissions you can copy them from an existing file in a Zip or check them here.

Eduardo Trápani
  • 12,834
-3

That is not possible.

ZIP file format does not originate from UNIX systems and it doesn't thus have any UNIX-related permission support.

raspi
  • 1,376