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=head1 NAME
Compress::Zlib::FAQ -- Frequently Asked Questions about Compress::Zlib
=head1 DESCRIPTION
Common questions answered.
=head2 Compatibility with Unix compress/uncompress.
Although C<Compress::Zlib> has a pair of functions called C<compress>
and C<uncompress>, they are I<not> the same as the Unix programs of the
same name. The C<Compress::Zlib> library is not compatible with Unix
C<compress>.
If you have the C<uncompress> program available, you can use this to
read compressed files
open F, "uncompress -c $filename |";
while (<F>)
{
...
If you have the C<gunzip> program available, you can use this to read
compressed files
open F, "gunzip -c $filename |";
while (<F>)
{
...
and this to write compress files if you have the C<compress> program
available
open F, "| compress -c $filename ";
print F "data";
...
close F ;
=head2 Accessing .tar.Z files
The C<Archive::Tar> module can optionally use C<Compress::Zlib> (via
the C<IO::Zlib> module) to access tar files that have been compressed
with C<gzip>. Unfortunately tar files compressed with the Unix C<compress>
utility cannot be read by C<Compress::Zlib> and so cannot be directly
accesses by C<Archive::Tar>.
If the C<uncompress> or C<gunzip> programs are available, you can use
one of these workarounds to read C<.tar.Z> files from C<Archive::Tar>
Firstly with C<uncompress>
use strict;
use warnings;
use Archive::Tar;
open F, "uncompress -c $filename |";
my $tar = Archive::Tar->new(*F);
...
and this with C<gunzip>
use strict;
use warnings;
use Archive::Tar;
open F, "gunzip -c $filename |";
my $tar = Archive::Tar->new(*F);
...
Similarly, if the C<compress> program is available, you can use this to
write a C<.tar.Z> file
use strict;
use warnings;
use Archive::Tar;
use IO::File;
my $fh = new IO::File "| compress -c >$filename";
my $tar = Archive::Tar->new();
...
$tar->write($fh);
$fh->close ;
=head2 Accessing Zip Files
Although it is possible (with some effort on your part) to use this
module to access .zip files, there is a module on CPAN that will do all
the hard work for you. Check out the C<Archive::Zip> module on CPAN at
http://www.cpan.org/modules/by-module/Archive/Archive-Zip-*.tar.gz
Assuming you don't want to use this module to access zip files there
are a number of undocumented features in the zlib library you need to
be aware of.
=over 5
=item 1.
When calling B<inflateInit> or B<deflateInit> the B<WindowBits> parameter
must be set to C<-MAX_WBITS>. This disables the creation of the zlib
header.
=item 2.
The zlib function B<inflate>, and so the B<inflate> method supplied in
this module, assume that there is at least one trailing byte after the
compressed data stream. Normally this isn't a problem because both
the gzip and zip file formats will guarantee that there is data directly
after the compressed data stream.
=back
=head2 Zlib Library Version Support
By default C<Compress::Zlib> will build with a private copy of version 1.2.3 of the zlib library. (See the F<README> file for details of how
to override this behavior)
If you decide to use a different version of the zlib library, you need to be
aware of the following issues
=over 5
=item *
First off, you must have zlib 1.0.5 or better.
=item *
You need to have zlib 1.2.1 or better if you want to use the C<-Merge> option
with C<IO::Compress::Gzip>, C<IO::Compress::Deflate> and C<IO::Compress::RawDeflate>.
=back
=head1 SEE ALSO
L<Compress::Zlib>, L<IO::Compress::Gzip>, L<IO::Uncompress::Gunzip>, L<IO::Compress::Deflate>, L<IO::Uncompress::Inflate>, L<IO::Compress::RawDeflate>, L<IO::Uncompress::RawInflate>, L<IO::Uncompress::AnyInflate>
L<Compress::Zlib::FAQ|Compress::Zlib::FAQ>
L<File::GlobMapper|File::GlobMapper>, L<Archive::Tar|Archive::Zip>,
L<IO::Zlib|IO::Zlib>
For RFC 1950, 1951 and 1952 see
F<http://www.faqs.org/rfcs/rfc1950.html>,
F<http://www.faqs.org/rfcs/rfc1951.html> and
F<http://www.faqs.org/rfcs/rfc1952.html>
The primary site for the gzip program is F<http://www.gzip.org>.
=head1 AUTHOR
The I<> module was written by Paul Marquess,
F<pmqs@cpan.org>. The latest copy of the module can be
found on CPAN in F<modules/by-module/Compress/Compress-Zlib-x.x.tar.gz>.
The I<zlib> compression library was written by Jean-loup Gailly
F<gzip@prep.ai.mit.edu> and Mark Adler F<madler@alumni.caltech.edu>.
The primary site for the I<zlib> compression library is
F<http://www.zlib.org>.
=head1 MODIFICATION HISTORY
See the Changes file.
=head1 COPYRIGHT AND LICENSE
Copyright (c) 2005 Paul Marquess. All rights reserved.
This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
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