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Archive::Zip::FAQ(3)  User Contributed Perl Documentation Archive::Zip::FAQ(3)

       Archive::Zip::FAQ - Answers to a few frequently asked questions about

       It seems that I keep answering the same questions over and over again.
       I assume that this is because my documentation is deficient, rather
       than that people don't read the documentation.

       So this FAQ is an attempt to cut down on the number of personal answers
       I have to give. At least I can now say "You did read the FAQ, right?".

       The questions are not in any particular order. The answers assume the
       current version of Archive::Zip; some of the answers depend on newly
       added/fixed functionality.

Install problems on RedHat 8 or 9 with Perl 5.8.0
       Q: Archive::Zip won't install on my RedHat 9 system! It's broke!

       A: This has become something of a FAQ.  Basically, RedHat broke some
       versions of Perl by setting LANG to UTF8.  They apparently have a fixed
       version out as an update.

       You might try running CPAN or creating your Makefile after exporting
       the LANG environment variable as



Why is my zip file so big?
       Q: My zip file is actually bigger than what I stored in it! Why?

       A: Some things to make sure of:

       Make sure that you are requesting COMPRESSION_DEFLATED if you are stor‐
       ing strings.
	   $member->desiredCompressionMethod( COMPRESSION_DEFLATED );

       Don't make lots of little files if you can help it.
	   Since zip computes the compression tables for each member, small
	   members without much entropy won't compress well.  Instead, if
	   you've got lots of repeated strings in your data, try to combine
	   them into one big member.

       Make sure that you are requesting COMPRESSION_STORED if you are storing
       things that are already compressed.
	   If you're storing a .zip, .jpg, .mp3, or other compressed file in a
	   zip, then don't compress them again. They'll get bigger.

Sample code?
       Q: Can you send me code to do (whatever)?

       A: Have you looked in the "examples/" directory yet? It contains:

       examples/	-- How to find out how big a Zip file will be
       before writing it
       examples/		-- Copies one Zip file to another
       examples/	-- extract file(s) from a Zip
       examples/	-- make and mail a zip file
       examples/		-- demo for use of MockFileHandle
       examples/	-- shows how to use IO::Scalar as the source
       of a Zip read
       examples/	-- a brief example of a self-extracting Zip
       examples/	-- uses Archive::Zip::Tree to unzip an entire
       examples/	-- shows how to read/modify/write a Zip
       examples/	-- shows how to update a Zip in place
       examples/	-- shows how to use IO::Scalar as the destina‐
       tion of a Zip write
       examples/ -- shows how to use IO::String as the destina‐
       tion of a Zip write
       examples/		-- Constructs a Zip file
       examples/	-- One way to check a Zip file for validity
       examples/	-- Prints out information about a Zip archive
       examples/	-- Searches for text in Zip files
       examples/	-- Lists a Zip file and checks member CRCs
       examples/	-- Puts recent files into a zipfile
       examples/	-- Another way to check a Zip file for valid‐

Can't Read/modify/write same Zip file
       Q: Why can't I open a Zip file, add a member, and write it back? I get
       an error message when I try.

       A: Because Archive::Zip doesn't (and can't, generally) read file con‐
       tents into memory, the original Zip file is required to stay around
       until the writing of the new file is completed.

       The best way to do this is to write the Zip to a temporary file and
       then rename the temporary file to have the old name (possibly after
       deleting the old one).

       Archive::Zip v1.02 added the archive methods "overwrite()" and "over‐
       writeAs()" to do this simply and carefully.

       See "examples/" for an example of this technique.

File creation time not set
       Q: Upon extracting files, I see that their modification (and access)
       times are set to the time in the Zip archive. However, their creation
       time is not set to the same time. Why?

       A: Mostly because Perl doesn't give cross-platform access to creation
       time.  Indeed, many systems (like Unix) don't support such a concept.
       However, if yours does, you can easily set it. Get the modification
       time from the member using "lastModTime()".

Can't use Archive::Zip on gzip files
       Q: Can I use Archive::Zip to extract Unix gzip files?

       A: No.

       There is a distinction between Unix gzip files, and Zip archives that
       also can use the gzip compression.

       Depending on the format of the gzip file, you can use Compress::Zlib,
       or Archive::Tar to decompress it (and de-archive it in the case of Tar

       You can unzip PKZIP/WinZip/etc/ archives using Archive::Zip (that's
       what it's for) as long as any compressed members are compressed using
       Deflate compression.

Add a directory/tree to a Zip
       Q: How can I add a directory (or tree) full of files to a Zip?

       A: You can use the Archive::Zip::addTree*() methods:

	  use Archive::Zip;
	  my $zip = Archive::Zip->new();
	  # add all readable files and directories below . as xyz/*
	  $zip->addTree( '.', 'xyz' );
	  # add all readable plain files below /abc as def/*
	  $zip->addTree( '/abc', 'def', sub { -f && -r } );
	  # add all .c files below /tmp as stuff/*
	  $zip->addTreeMatching( '/tmp', 'stuff', '\.c$' );
	  # add all .o files below /tmp as stuff/* if they aren't writable
	  $zip->addTreeMatching( '/tmp', 'stuff', '\.o$', sub { ! -w } );
	  # add all .so files below /tmp that are smaller than 200 bytes as stuff/*
	  $zip->addTreeMatching( '/tmp', 'stuff', '\.o$', sub { -s < 200 } );
	  # and write them into a file

Extract a directory/tree
       Q: How can I extract some (or all) files from a Zip into a different

       A: You can use the Archive::Zip::extractTree() method: ??? ⎪⎪

	  # now extract the same files into /tmpx
	  $zip->extractTree( 'stuff', '/tmpx' );

Update a directory/tree
       Q: How can I update a Zip from a directory tree, adding or replacing
       only the newer files?

       A: You can use the Archive::Zip::updateTree() method that was added in
       version 1.09.

Zip times might be off by 1 second
       Q: It bothers me greatly that my file times are wrong by one second
       about half the time. Why don't you do something about it?

       A: Get over it. This is a result of the Zip format storing times in DOS
       format, which has a resolution of only two seconds.

Zip times don't include time zone information
       Q: My file times don't respect time zones. What gives?

       A: If this is important to you, please submit patches to read the vari‐
       ous Extra Fields that encode times with time zones. I'm just using the
       DOS Date/Time, which doesn't have a time zone.

How do I make a self-extracting Zip
       Q: I want to make a self-extracting Zip file. Can I do this?

       A: Yes. You can write a self-extracting archive stub (that is, a ver‐
       sion of unzip) to the output filehandle that you pass to writeToFile‐
       Handle(). See examples/ for how to write a self-extracting ar‐

       However, you should understand that this will only work on one kind of
       platform (the one for which the stub was compiled).

How can I deal with Zips with prepended garbage (i.e. from Sircam)
       Q: How can I tell if a Zip has been damaged by adding garbage to the
       beginning or inside the file?

       A: I added code for this for the Amavis virus scanner. You can query
       archives for their 'eocdOffset' property, which should be 0:

	 if ($zip->eocdOffset > 0)
	   { warn($zip->eocdOffset . " bytes of garbage at beginning or within Zip") }

       When members are extracted, this offset will be used to adjust the
       start of the member if necessary.

Can't extract Shrunk files
       Q: I'm trying to extract a file out of a Zip produced by PKZIP, and
       keep getting this error message:

	 error: Unsupported compression combination: read 6, write 0

       A: You can't uncompress this archive member. Archive::Zip only supports
       uncompressed members, and compressed members that are compressed using
       the compression supported by Compress::Zlib. That means only Deflated
       and Stored members.

       Your file is compressed using the Shrink format, which isn't supported
       by Compress::Zlib.

       You could, perhaps, use a command-line UnZip program (like the Info-Zip
       one) to extract this.

Can't do decryption
       Q: How do I decrypt encrypted Zip members?

       A: With some other program or library. Archive::Zip doesn't support
       decryption, and probably never will (unless you write it).

How to test file integrity?
       Q: How can Archive::Zip can test the validity of a Zip file?

       A: If you try to decompress the file, the gzip streams will report
       errors if you have garbage. Most of the time.

       If you try to open the file and a central directory structure can't be
       found, an error will be reported.

       When a file is being read, if we can't find a proper PK.. signature in
       the right places we report a format error.

       If there is added garbage at the beginning of a Zip file (as inserted
       by some viruses), you can find out about it, but Archive::Zip will
       ignore it, and you can still use the archive. When it gets written back
       out the added stuff will be gone.

       There are two ready-to-use utilities in the examples directory that can
       be used to test file integrity, or that you can use as examples for
       your own code:

       examples/ shows how to use an attempted extraction to test a
       examples/ shows how to test CRCs in a file.

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 $zip->memberNamed($someName);

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

File ownership/permissions/ACLS/etc
       Q: Why doesn't Archive::Zip deal with file ownership, ACLs, etc.?

       A: There is no standard way to represent these in the Zip file format.
       If you want to send me code to properly handle the various extra fields
       that have been used to represent these through the years, I'll look at

I can't compile but ActiveState only has an old version of Archive::Zip
       Q: I've only installed modules using ActiveState's PPM program and
       repository. But they have a much older version of Archive::Zip than is
       in CPAN. Will you send me a newer PPM?

       A: Probably not, unless I get lots of extra time. But there's no reason
       you can't install the version from CPAN. Archive::Zip is pure Perl, so
       all you need is NMAKE, which you can get for free from Microsoft (see
       the FAQ in the ActiveState documentation for details on how to install
       CPAN modules).

My JPEGs (or MP3's) don't compress when I put them into Zips!
       Q: How come my JPEGs and MP3's don't compress much when I put them into

       A: Because they're already compressed.

Under Windows, things lock up/get damaged
       Q: I'm using Windows. When I try to use Archive::Zip, my machine locks
       up/makes funny sounds/displays a BSOD/corrupts data. How can I fix

       A: First, try the newest version of Compress::Zlib. I know of Windows-
       related problems prior to v1.14 of that library.

       If that doesn't get rid of the problem, fix your computer or get rid of

Zip contents in a scalar
       Q: I want to read a Zip file from (or write one to) a scalar variable
       instead of a file. How can I do this?

       A: Use "IO::String" and the "readFromFileHandle()" and "writeToFileHan‐
       dle()" methods.	See "examples/" and "exam‐

Reading from streams
       Q: How do I read from a stream (like for the Info-Zip "funzip" pro‐

       A:   This isn't currently supported, though writing to a stream is.

perl v5.8.8			  2008-10-12		  Archive::Zip::FAQ(3)

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