5 Archive::Zip::FAQ - Answers to a few frequently asked questions about Archive::Zip
10 It seems that I keep answering the same questions over and over again. I
11 assume that this is because my documentation is deficient, rather than that
12 people don't read the documentation.
15 So this FAQ is an attempt to cut down on the number of personal answers I have
16 to give. At least I can now say "You I<did> read the FAQ, right?".
19 The questions are not in any particular order. The answers assume the current
20 version of Archive::Zip; some of the answers depend on newly added/fixed
23 =head1 Install problems on RedHat 8 or 9 with Perl 5.8.0
26 B<Q:> Archive::Zip won't install on my RedHat 9 system! It's broke!
29 B<A:> This has become something of a FAQ.
30 Basically, RedHat broke some versions of Perl by setting LANG to UTF8.
31 They apparently have a fixed version out as an update.
33 You might try running CPAN or creating your Makefile after exporting the LANG
34 environment variable as
38 L<https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=87682>
41 =head1 Why is my zip file so big?
44 B<Q:> My zip file is actually bigger than what I stored in it! Why?
47 B<A:> Some things to make sure of:
51 =item Make sure that you are requesting COMPRESSION_DEFLATED if you are storing strings.
56 $member->desiredCompressionMethod( COMPRESSION_DEFLATED );
59 =item Don't make lots of little files if you can help it.
63 Since zip computes the compression tables for each member, small
64 members without much entropy won't compress well. Instead, if you've
65 got lots of repeated strings in your data, try to combine them into
69 =item Make sure that you are requesting COMPRESSION_STORED if you are storing things that are already compressed.
73 If you're storing a .zip, .jpg, .mp3, or other compressed file in a zip,
74 then don't compress them again. They'll get bigger.
81 B<Q:> Can you send me code to do (whatever)?
84 B<A:> Have you looked in the C<examples/> directory yet? It contains:
88 =item examples/calcSizes.pl -- How to find out how big a Zip file will be before writing it
92 =item examples/copy.pl -- Copies one Zip file to another
96 =item examples/extract.pl -- extract file(s) from a Zip
100 =item examples/mailZip.pl -- make and mail a zip file
104 =item examples/mfh.pl -- demo for use of MockFileHandle
108 =item examples/readScalar.pl -- shows how to use IO::Scalar as the source of a Zip read
112 =item examples/selfex.pl -- a brief example of a self-extracting Zip
116 =item examples/unzipAll.pl -- uses Archive::Zip::Tree to unzip an entire Zip
120 =item examples/updateZip.pl -- shows how to read/modify/write a Zip
124 =item examples/updateTree.pl -- shows how to update a Zip in place
128 =item examples/writeScalar.pl -- shows how to use IO::Scalar as the destination of a Zip write
132 =item examples/writeScalar2.pl -- shows how to use IO::String as the destination of a Zip write
136 =item examples/zip.pl -- Constructs a Zip file
140 =item examples/zipcheck.pl -- One way to check a Zip file for validity
144 =item examples/zipinfo.pl -- Prints out information about a Zip archive file
148 =item examples/zipGrep.pl -- Searches for text in Zip files
152 =item examples/ziptest.pl -- Lists a Zip file and checks member CRCs
156 =item examples/ziprecent.pl -- Puts recent files into a zipfile
160 =item examples/ziptest.pl -- Another way to check a Zip file for validity
166 =head1 Can't Read/modify/write same Zip file
169 B<Q:> Why can't I open a Zip file, add a member, and write it back? I get an
170 error message when I try.
173 B<A:> Because Archive::Zip doesn't (and can't, generally) read file contents into memory,
174 the original Zip file is required to stay around until the writing of the new
178 The best way to do this is to write the Zip to a temporary file and then
179 rename the temporary file to have the old name (possibly after deleting the
183 Archive::Zip v1.02 added the archive methods C<overwrite()> and
184 C<overwriteAs()> to do this simply and carefully.
187 See C<examples/updateZip.pl> for an example of this technique.
189 =head1 File creation time not set
192 B<Q:> Upon extracting files, I see that their modification (and access) times are
193 set to the time in the Zip archive. However, their creation time is not set to
197 B<A:> Mostly because Perl doesn't give cross-platform access to I<creation time>.
198 Indeed, many systems (like Unix) don't support such a concept.
199 However, if yours does, you can easily set it. Get the modification time from
200 the member using C<lastModTime()>.
202 =head1 Can't use Archive::Zip on gzip files
205 B<Q:> Can I use Archive::Zip to extract Unix gzip files?
211 There is a distinction between Unix gzip files, and Zip archives that
212 also can use the gzip compression.
215 Depending on the format of the gzip file, you can use L<Compress::Zlib>, or
216 L<Archive::Tar> to decompress it (and de-archive it in the case of Tar files).
219 You can unzip PKZIP/WinZip/etc/ archives using Archive::Zip (that's what
220 it's for) as long as any compressed members are compressed using
223 =head1 Add a directory/tree to a Zip
226 B<Q:> How can I add a directory (or tree) full of files to a Zip?
229 B<A:> You can use the Archive::Zip::addTree*() methods:
232 my $zip = Archive::Zip->new();
233 # add all readable files and directories below . as xyz/*
234 $zip->addTree( '.', 'xyz' );
235 # add all readable plain files below /abc as def/*
236 $zip->addTree( '/abc', 'def', sub { -f && -r } );
237 # add all .c files below /tmp as stuff/*
238 $zip->addTreeMatching( '/tmp', 'stuff', '\.c$' );
239 # add all .o files below /tmp as stuff/* if they aren't writable
240 $zip->addTreeMatching( '/tmp', 'stuff', '\.o$', sub { ! -w } );
241 # add all .so files below /tmp that are smaller than 200 bytes as stuff/*
242 $zip->addTreeMatching( '/tmp', 'stuff', '\.o$', sub { -s < 200 } );
243 # and write them into a file
244 $zip->writeToFileNamed('xxx.zip');
246 =head1 Extract a directory/tree
249 B<Q:> How can I extract some (or all) files from a Zip into a different
253 B<A:> You can use the Archive::Zip::extractTree() method:
257 # now extract the same files into /tmpx
258 $zip->extractTree( 'stuff', '/tmpx' );
260 =head1 Update a directory/tree
263 B<Q:> How can I update a Zip from a directory tree, adding or replacing only
267 B<A:> You can use the Archive::Zip::updateTree() method that was added in version 1.09.
269 =head1 Zip times might be off by 1 second
272 B<Q:> It bothers me greatly that my file times are wrong by one second about half
273 the time. Why don't you do something about it?
276 B<A:> Get over it. This is a result of the Zip format storing times in DOS
277 format, which has a resolution of only two seconds.
279 =head1 Zip times don't include time zone information
282 B<Q:> My file times don't respect time zones. What gives?
285 B<A:> If this is important to you, please submit patches to read the various
286 Extra Fields that encode times with time zones. I'm just using the DOS
287 Date/Time, which doesn't have a time zone.
289 =head1 How do I make a self-extracting Zip
292 B<Q:> I want to make a self-extracting Zip file. Can I do this?
295 B<A:> Yes. You can write a self-extracting archive stub (that is, a version of
296 unzip) to the output filehandle that you pass to writeToFileHandle(). See
297 examples/selfex.pl for how to write a self-extracting archive.
300 However, you should understand that this will only work on one kind of
301 platform (the one for which the stub was compiled).
303 =head1 How can I deal with Zips with prepended garbage (i.e. from Sircam)
306 B<Q:> How can I tell if a Zip has been damaged by adding garbage to the
307 beginning or inside the file?
310 B<A:> I added code for this for the Amavis virus scanner. You can query archives
311 for their 'eocdOffset' property, which should be 0:
314 if ($zip->eocdOffset > 0)
315 { warn($zip->eocdOffset . " bytes of garbage at beginning or within Zip") }
318 When members are extracted, this offset will be used to adjust the start of
319 the member if necessary.
321 =head1 Can't extract Shrunk files
324 B<Q:> I'm trying to extract a file out of a Zip produced by PKZIP, and keep
325 getting this error message:
328 error: Unsupported compression combination: read 6, write 0
331 B<A:> You can't uncompress this archive member. Archive::Zip only supports uncompressed
332 members, and compressed members that are compressed using the compression
333 supported by Compress::Zlib. That means only Deflated and Stored members.
336 Your file is compressed using the Shrink format, which isn't supported by
340 You could, perhaps, use a command-line UnZip program (like the Info-Zip
341 one) to extract this.
343 =head1 Can't do decryption
346 B<Q:> How do I decrypt encrypted Zip members?
349 B<A:> With some other program or library. Archive::Zip doesn't support decryption,
350 and probably never will (unless I<you> write it).
352 =head1 How to test file integrity?
355 B<Q:> How can Archive::Zip can test the validity of a Zip file?
358 B<A:> If you try to decompress the file, the gzip streams will report errors
359 if you have garbage. Most of the time.
361 If you try to open the file and a central directory structure can't be
362 found, an error will be reported.
364 When a file is being read, if we can't find a proper PK.. signature in
365 the right places we report a format error.
367 If there is added garbage at the beginning of a Zip file (as inserted
368 by some viruses), you can find out about it, but Archive::Zip will ignore it,
369 and you can still use the archive. When it gets written back out the
370 added stuff will be gone.
373 There are two ready-to-use utilities in the examples directory that can
374 be used to test file integrity, or that you can use as examples
379 =item examples/zipcheck.pl shows how to use an attempted extraction to test a file.
383 =item examples/ziptest.pl shows how to test CRCs in a file.
389 =head1 Duplicate files in Zip?
392 B<Q:> Archive::Zip let me put the same file in my Zip twice! Why don't you prevent this?
395 B<A:> As far as I can tell, this is not disallowed by the Zip spec. If you
396 think it's a bad idea, check for it yourself:
399 $zip->addFile($someFile, $someName) unless $zip->memberNamed($someName);
402 I can even imagine cases where this might be useful (for instance, multiple
405 =head1 File ownership/permissions/ACLS/etc
408 B<Q:> Why doesn't Archive::Zip deal with file ownership, ACLs, etc.?
411 B<A:> There is no standard way to represent these in the Zip file format. If
412 you want to send me code to properly handle the various extra fields that
413 have been used to represent these through the years, I'll look at it.
415 =head1 I can't compile but ActiveState only has an old version of Archive::Zip
418 B<Q:> I've only installed modules using ActiveState's PPM program and
419 repository. But they have a much older version of Archive::Zip than is in CPAN. Will
420 you send me a newer PPM?
423 B<A:> Probably not, unless I get lots of extra time. But there's no reason you
424 can't install the version from CPAN. Archive::Zip is pure Perl, so all you need is
425 NMAKE, which you can get for free from Microsoft (see the FAQ in the
426 ActiveState documentation for details on how to install CPAN modules).
428 =head1 My JPEGs (or MP3's) don't compress when I put them into Zips!
431 B<Q:> How come my JPEGs and MP3's don't compress much when I put them into Zips?
434 B<A:> Because they're already compressed.
436 =head1 Under Windows, things lock up/get damaged
439 B<Q:> I'm using Windows. When I try to use Archive::Zip, my machine locks up/makes
440 funny sounds/displays a BSOD/corrupts data. How can I fix this?
443 B<A:> First, try the newest version of Compress::Zlib. I know of
444 Windows-related problems prior to v1.14 of that library.
447 If that doesn't get rid of the problem, fix your computer or get rid of
450 =head1 Zip contents in a scalar
453 B<Q:> I want to read a Zip file from (or write one to) a scalar variable instead
454 of a file. How can I do this?
457 B<A:> Use C<IO::Scalar> and the C<readFromFileHandle()> and
458 C<writeToFileHandle()> methods.
459 See C<examples/readScalar.pl> and C<examples/writeScalar.pl>.
461 =head1 Reading from streams
464 B<Q:> How do I read from a stream (like for the Info-Zip C<funzip> program)?
467 B<A:> This isn't currently supported, though writing to a stream is.