1Archive::Zip::FAQ(3)  User Contributed Perl Documentation Archive::Zip::FAQ(3)
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NAME

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

10       It seems that I keep answering the same questions over and over again.
11       I assume that this is because my documentation is deficient, rather
12       than that people don't read the documentation.
13
14       So this FAQ is an attempt to cut down on the number of personal answers
15       I have to give. At least I can now say "You did read the FAQ, right?".
16
17       The questions are not in any particular order. The answers assume the
18       current version of Archive::Zip; some of the answers depend on newly
19       added/fixed functionality.
20

Install problems on RedHat 8 or 9 with Perl 5.8.0

22       Q: Archive::Zip won't install on my RedHat 9 system! It's broke!
23
24       A: This has become something of a FAQ.  Basically, RedHat broke some
25       versions of Perl by setting LANG to UTF8.  They apparently have a fixed
26       version out as an update.
27
28       You might try running CPAN or creating your Makefile after exporting
29       the LANG environment variable as
30
31       "LANG=C"
32
33       <https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=87682>
34

Why is my zip file so big?

36       Q: My zip file is actually bigger than what I stored in it! Why?
37
38       A: Some things to make sure of:
39
40       Make sure that you are requesting COMPRESSION_DEFLATED if you are
41       storing strings.
42           $member->desiredCompressionMethod( COMPRESSION_DEFLATED );
43
44       Don't make lots of little files if you can help it.
45           Since zip computes the compression tables for each member, small
46           members without much entropy won't compress well.  Instead, if
47           you've got lots of repeated strings in your data, try to combine
48           them into one big member.
49
50       Make sure that you are requesting COMPRESSION_STORED if you are storing
51       things that are already compressed.
52           If you're storing a .zip, .jpg, .mp3, or other compressed file in a
53           zip, then don't compress them again. They'll get bigger.
54

Sample code?

56       Q: Can you send me code to do (whatever)?
57
58       A: Have you looked in the "examples/" directory yet? It contains:
59
60       examples/calcSizes.pl    -- How to find out how big a Zip file will be
61       before writing it
62       examples/copy.pl         -- Copies one Zip file to another
63       examples/extract.pl      -- extract file(s) from a Zip
64       examples/mailZip.pl      -- make and mail a zip file
65       examples/mfh.pl          -- demo for use of MockFileHandle
66       examples/readScalar.pl   -- shows how to use IO::Scalar as the source
67       of a Zip read
68       examples/selfex.pl       -- a brief example of a self-extracting Zip
69       examples/unzipAll.pl     -- uses Archive::Zip::Tree to unzip an entire
70       Zip
71       examples/updateZip.pl    -- shows how to read/modify/write a Zip
72       examples/updateTree.pl   -- shows how to update a Zip in place
73       examples/writeScalar.pl  -- shows how to use IO::Scalar as the
74       destination of a Zip write
75       examples/writeScalar2.pl -- shows how to use IO::String as the
76       destination of a Zip write
77       examples/zip.pl          -- Constructs a Zip file
78       examples/zipcheck.pl     -- One way to check a Zip file for validity
79       examples/zipinfo.pl      -- Prints out information about a Zip archive
80       file
81       examples/zipGrep.pl      -- Searches for text in Zip files
82       examples/ziptest.pl      -- Lists a Zip file and checks member CRCs
83       examples/ziprecent.pl    -- Puts recent files into a zipfile
84       examples/ziptest.pl      -- Another way to check a Zip file for
85       validity
86

Can't Read/modify/write same Zip file

88       Q: Why can't I open a Zip file, add a member, and write it back? I get
89       an error message when I try.
90
91       A: Because Archive::Zip doesn't (and can't, generally) read file
92       contents into memory, the original Zip file is required to stay around
93       until the writing of the new file is completed.
94
95       The best way to do this is to write the Zip to a temporary file and
96       then rename the temporary file to have the old name (possibly after
97       deleting the old one).
98
99       Archive::Zip v1.02 added the archive methods "overwrite()" and
100       "overwriteAs()" to do this simply and carefully.
101
102       See "examples/updateZip.pl" for an example of this technique.
103

File creation time not set

105       Q: Upon extracting files, I see that their modification (and access)
106       times are set to the time in the Zip archive. However, their creation
107       time is not set to the same time. Why?
108
109       A: Mostly because Perl doesn't give cross-platform access to creation
110       time.  Indeed, many systems (like Unix) don't support such a concept.
111       However, if yours does, you can easily set it. Get the modification
112       time from the member using "lastModTime()".
113

Can't use Archive::Zip on gzip files

115       Q: Can I use Archive::Zip to extract Unix gzip files?
116
117       A: No.
118
119       There is a distinction between Unix gzip files, and Zip archives that
120       also can use the gzip compression.
121
122       Depending on the format of the gzip file, you can use
123       Compress::Raw::Zlib, or Archive::Tar to decompress it (and de-archive
124       it in the case of Tar files).
125
126       You can unzip PKZIP/WinZip/etc/ archives using Archive::Zip (that's
127       what it's for) as long as any compressed members are compressed using
128       Deflate compression.
129

Add a directory/tree to a Zip

131       Q: How can I add a directory (or tree) full of files to a Zip?
132
133       A: You can use the Archive::Zip::addTree*() methods:
134
135          use Archive::Zip;
136          my $zip = Archive::Zip->new();
137          # add all readable files and directories below . as xyz/*
138          $zip->addTree( '.', 'xyz' );
139          # add all readable plain files below /abc as def/*
140          $zip->addTree( '/abc', 'def', sub { -f && -r } );
141          # add all .c files below /tmp as stuff/*
142          $zip->addTreeMatching( '/tmp', 'stuff', '\.c$' );
143          # add all .o files below /tmp as stuff/* if they aren't writable
144          $zip->addTreeMatching( '/tmp', 'stuff', '\.o$', sub { ! -w } );
145          # add all .so files below /tmp that are smaller than 200 bytes as stuff/*
146          $zip->addTreeMatching( '/tmp', 'stuff', '\.o$', sub { -s < 200 } );
147          # and write them into a file
148          $zip->writeToFileNamed('xxx.zip');
149

Extract a directory/tree

151       Q: How can I extract some (or all) files from a Zip into a different
152       directory?
153
154       A: You can use the Archive::Zip::extractTree() method: ??? ||
155
156          # now extract the same files into /tmpx
157          $zip->extractTree( 'stuff', '/tmpx' );
158

Update a directory/tree

160       Q: How can I update a Zip from a directory tree, adding or replacing
161       only the newer files?
162
163       A: You can use the Archive::Zip::updateTree() method that was added in
164       version 1.09.
165

Zip times might be off by 1 second

167       Q: It bothers me greatly that my file times are wrong by one second
168       about half the time. Why don't you do something about it?
169
170       A: Get over it. This is a result of the Zip format storing times in DOS
171       format, which has a resolution of only two seconds.
172

Zip times don't include time zone information

174       Q: My file times don't respect time zones. What gives?
175
176       A: If this is important to you, please submit patches to read the
177       various Extra Fields that encode times with time zones. I'm just using
178       the DOS Date/Time, which doesn't have a time zone.
179

How do I make a self-extracting Zip

181       Q: I want to make a self-extracting Zip file. Can I do this?
182
183       A: Yes. You can write a self-extracting archive stub (that is, a
184       version of unzip) to the output filehandle that you pass to
185       writeToFileHandle(). See examples/selfex.pl for how to write a self-
186       extracting archive.
187
188       However, you should understand that this will only work on one kind of
189       platform (the one for which the stub was compiled).
190

How can I deal with Zips with prepended garbage (i.e. from Sircam)

192       Q: How can I tell if a Zip has been damaged by adding garbage to the
193       beginning or inside the file?
194
195       A: I added code for this for the Amavis virus scanner. You can query
196       archives for their 'eocdOffset' property, which should be 0:
197
198         if ($zip->eocdOffset > 0)
199           { warn($zip->eocdOffset . " bytes of garbage at beginning or within Zip") }
200
201       When members are extracted, this offset will be used to adjust the
202       start of the member if necessary.
203

Can't extract Shrunk files

205       Q: I'm trying to extract a file out of a Zip produced by PKZIP, and
206       keep getting this error message:
207
208         error: Unsupported compression combination: read 6, write 0
209
210       A: You can't uncompress this archive member. Archive::Zip only supports
211       uncompressed members, and compressed members that are compressed using
212       the compression supported by Compress::Raw::Zlib. That means only
213       Deflated and Stored members.
214
215       Your file is compressed using the Shrink format, which is not supported
216       by Compress::Raw::Zlib.
217
218       You could, perhaps, use a command-line UnZip program (like the Info-Zip
219       one) to extract this.
220

Can't do decryption

222       Q: How do I decrypt encrypted Zip members?
223
224       A: With some other program or library. Archive::Zip doesn't support
225       decryption, and probably never will (unless you write it).
226

How to test file integrity?

228       Q: How can Archive::Zip can test the validity of a Zip file?
229
230       A: If you try to decompress the file, the gzip streams will report
231       errors if you have garbage. Most of the time.
232
233       If you try to open the file and a central directory structure can't be
234       found, an error will be reported.
235
236       When a file is being read, if we can't find a proper PK.. signature in
237       the right places we report a format error.
238
239       If there is added garbage at the beginning of a Zip file (as inserted
240       by some viruses), you can find out about it, but Archive::Zip will
241       ignore it, and you can still use the archive. When it gets written back
242       out the added stuff will be gone.
243
244       There are two ready-to-use utilities in the examples directory that can
245       be used to test file integrity, or that you can use as examples for
246       your own code:
247
248       examples/zipcheck.pl shows how to use an attempted extraction to test a
249       file.
250       examples/ziptest.pl shows how to test CRCs in a file.
251

Duplicate files in Zip?

253       Q: Archive::Zip let me put the same file in my Zip twice! Why don't you
254       prevent this?
255
256       A: As far as I can tell, this is not disallowed by the Zip spec. If you
257       think it's a bad idea, check for it yourself:
258
259         $zip->addFile($someFile, $someName) unless $zip->memberNamed($someName);
260
261       I can even imagine cases where this might be useful (for instance,
262       multiple versions of files).
263

File ownership/permissions/ACLS/etc

265       Q: Why doesn't Archive::Zip deal with file ownership, ACLs, etc.?
266
267       A: There is no standard way to represent these in the Zip file format.
268       If you want to send me code to properly handle the various extra fields
269       that have been used to represent these through the years, I'll look at
270       it.
271

I can't compile but ActiveState only has an old version of Archive::Zip

273       Q: I've only installed modules using ActiveState's PPM program and
274       repository. But they have a much older version of Archive::Zip than is
275       in CPAN. Will you send me a newer PPM?
276
277       A: Probably not, unless I get lots of extra time. But there's no reason
278       you can't install the version from CPAN. Archive::Zip is pure Perl, so
279       all you need is NMAKE, which you can get for free from Microsoft (see
280       the FAQ in the ActiveState documentation for details on how to install
281       CPAN modules).
282

My JPEGs (or MP3's) don't compress when I put them into Zips!

284       Q: How come my JPEGs and MP3's don't compress much when I put them into
285       Zips?
286
287       A: Because they're already compressed.
288

Under Windows, things lock up/get damaged

290       Q: I'm using Windows. When I try to use Archive::Zip, my machine locks
291       up/makes funny sounds/displays a BSOD/corrupts data. How can I fix
292       this?
293
294       A: First, try the newest version of Compress::Raw::Zlib. I know of
295       Windows-related problems prior to v1.14 of that library.
296

Zip contents in a scalar

298       Q: I want to read a Zip file from (or write one to) a scalar variable
299       instead of a file. How can I do this?
300
301       A: Use "IO::String" and the "readFromFileHandle()" and
302       "writeToFileHandle()" methods.  See "examples/readScalar.pl" and
303       "examples/writeScalar.pl".
304

Reading from streams

306       Q: How do I read from a stream (like for the Info-Zip "funzip"
307       program)?
308
309       A: This is not currently supported, though writing to a stream is.
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313perl v5.32.0                      2020-07-28              Archive::Zip::FAQ(3)
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