0x1af4  0Ŀ#l4( ) *W+uLZ7 }? =head1 NAME IO::Compress::FAQ -- Frequently Asked Questions about IO::Compress =head1 DESCRIPTION Common questions answered. =head1 GENERAL =head2 Compatibility with Unix compress/uncompress. Although C has a pair of functions called C and C, they are I related to the Unix programs of the same name. The C module is not compatible with Unix C. If you have the C program available, you can use this to read compressed files open F, "uncompress -c $filename |"; while () { ... Alternatively, if you have the C program available, you can use this to read compressed files open F, "gunzip -c $filename |"; while () { ... and this to write compress files, if you have the C program available open F, "| compress -c $filename "; print F "data"; ... close F ; =head2 Accessing .tar.Z files The C module can optionally use C (via the C module) to access tar files that have been compressed with C. Unfortunately tar files compressed with the Unix C utility cannot be read by C and so cannot be directly accessed by C. If the C or C programs are available, you can use one of these workarounds to read C<.tar.Z> files from C Firstly with C use strict; use warnings; use Archive::Tar; open F, "uncompress -c $filename |"; my $tar = Archive::Tar->new(*F); ... and this with C use strict; use warnings; use Archive::Tar; open F, "gunzip -c $filename |"; my $tar = Archive::Tar->new(*F); ... Similarly, if the C 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 $fh = IO::File->new( "| compress -c >$filename" ); my $tar = Archive::Tar->new(); ... $tar->write($fh); $fh->close ; =head2 How do I recompress using a different compression? This is easier that you might expect if you realise that all the C objects are derived from C and that all the C modules can read from an C filehandle. So, for example, say you have a file compressed with gzip that you want to recompress with bzip2. Here is all that is needed to carry out the recompression. use IO::Uncompress::Gunzip ':all'; use IO::Compress::Bzip2 ':all'; my $gzipFile = "somefile.gz"; my $bzipFile = "somefile.bz2"; my $gunzip = IO::Uncompress::Gunzip->new( $gzipFile ) or die "Cannot gunzip $gzipFile: $GunzipError\n" ; bzip2 $gunzip => $bzipFile or die "Cannot bzip2 to $bzipFile: $Bzip2Error\n" ; Note, there is a limitation of this technique. Some compression file formats store extra information along with the compressed data payload. For example, gzip can optionally store the original filename and Zip stores a lot of information about the original file. If the original compressed file contains any of this extra information, it will not be transferred to the new compressed file using the technique above. =head1 ZIP =head2 What Compression Types do IO::Compress::Zip & IO::Uncompress::Unzip support? The following compression formats are supported by C and C =over 5 =item * Store (method 0) No compression at all. =item * Deflate (method 8) This is the default compression used when creating a zip file with C. =item * Bzip2 (method 12) Only supported if the C module is installed. =item * Lzma (method 14) Only supported if the C module is installed. =back =head2 Can I Read/Write Zip files larger the 4 Gig? Yes, both the C and C modules support the zip feature called I. That allows them to read/wri