Multiple copies of the same file in same ZIP archive

[bofh_of_oz]

In a script i'm working on, I create a ZIP archive and add a file to it. Or, if the zip file exists, just add the file to it. I have noticed a strange thing: I tell the script to add the same file to the ZIP archive many times, then open the archive with Winzip and what do I see? There are indeed many files inside - with the same filename! When I try to rename/delete those files, each of them is treated independently of others.

Even though this behaviour seems logical to me, I cannot reproduce the same functionality when I use PKZIP/Winzip/any other utility... Is that an 'undocumented feature' of Perl or what?

The code used is here:

use Archive::Zip qw(:CONSTANTS :ERROR_CODES);
use IO::Scalar;

my $fname = 'file1.txt';
my $zipfile = 'filename.zip';
my $zip = Archive::Zip -> new();
if (-e $zipfile)
{
   $zip ->read($zipfile);
} 

my $member = $zip->memberNamed( $fname );
if ($member eq undef)
{
   $member = $zip->addFile( $fname );
}

$member -> desiredCompressionLevel( 9 );

$fname = 'autotransParams.txt';
$member = $zip->memberNamed( $fname );
if ($member eq undef)
{
   $member = $zip->addFile( $fname );
}

$member -> desiredCompressionLevel( 9 );
my $status = $zip -> overwriteAs($zipfile);

[thundergnat]

Is that an 'undocumented feature' of Perl or what?

Actually, that appears to be a documented feature of Archive::Zip

Selected quote from Archive::Zip::FAQ.

---

Duplicate files in Zip?

Q: Archive::Zip let me put the same file in my Zip twice! Why don't you prevent this?

A: As far as I can tell, this is not disallowed by the Zip spec. If you think it's a bad idea, check for it yourself:

  $zip->addFile($someFile, $someName) unless $zip->memberNamed($someNa
+me);

I can even imagine cases where this might be useful (for instance, multiple versions of files).

---

See perldoc Archive::Zip::FAQ for further info.

[marnanel]

Well, the original file format specification didn't say anything about multiple filenames sharing the same name, so it's not actually contrary to the spec. It's easy enough to check for an existing file and delete it if found before adding the new one: after all, that's what WinZip and friends are doing behind the scenes anyway.

[PodMaster]

Is that an 'undocumented feature' of Perl or what?

Definetly no. If Winzip/pkzip/whatever can read such archives, then its probably an unused/unadvertised and/or unintentional feature of the format.