gzip.pm

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=over 5

=item A filename

If the C<$output> parameter is a simple scalar, it is assumed to be a
filename.  This file will be opened for writing and the compressed
data will be written to it.

=item A filehandle

If the C<$output> parameter is a filehandle, the compressed data
will be written to it.
The string '-' can be used as an alias for standard output.


=item A scalar reference 

If C<$output> is a scalar reference, the compressed data will be
stored in C<$$output>.



=item An Array Reference

If C<$output> is an array reference, the compressed data will be
pushed onto the array.

=item An Output FileGlob

If C<$output> is a string that is delimited by the characters "<" and ">"
C<gzip> will assume that it is an I<output fileglob string>. The
output is the list of files that match the fileglob.

When C<$output> is an fileglob string, C<$input> must also be a fileglob
string. Anything else is an error.

=back

If the C<$output> parameter is any other type, C<undef> will be returned.



=head2 Notes



When C<$input> maps to multiple files/buffers and C<$output> is a single
file/buffer the input files/buffers will be stored
in C<$output> as a concatenated series of compressed data streams.






=head2 Optional Parameters

Unless specified below, the optional parameters for C<gzip>,
C<OPTS>, are the same as those used with the OO interface defined in the
L</"Constructor Options"> section below.

=over 5

=item C<< AutoClose => 0|1 >>

This option applies to any input or output data streams to 
C<gzip> that are filehandles.

If C<AutoClose> is specified, and the value is true, it will result in all
input and/or output filehandles being closed once C<gzip> has
completed.

This parameter defaults to 0.


=item C<< BinModeIn => 0|1 >>

When reading from a file or filehandle, set C<binmode> before reading.

Defaults to 0.





=item C<< Append => 0|1 >>

TODO



=back



=head2 Examples

To read the contents of the file C<file1.txt> and write the compressed
data to the file C<file1.txt.gz>.

    use strict ;
    use warnings ;
    use IO::Compress::Gzip qw(gzip $GzipError) ;

    my $input = "file1.txt";
    gzip $input => "$input.gz"
        or die "gzip failed: $GzipError\n";


To read from an existing Perl filehandle, C<$input>, and write the
compressed data to a buffer, C<$buffer>.

    use strict ;
    use warnings ;
    use IO::Compress::Gzip qw(gzip $GzipError) ;
    use IO::File ;

    my $input = new IO::File "<file1.txt"
        or die "Cannot open 'file1.txt': $!\n" ;
    my $buffer ;
    gzip $input => \$buffer 
        or die "gzip failed: $GzipError\n";

To compress all files in the directory "/my/home" that match "*.txt"
and store the compressed data in the same directory

    use strict ;
    use warnings ;
    use IO::Compress::Gzip qw(gzip $GzipError) ;

    gzip '</my/home/*.txt>' => '<*.gz>'
        or die "gzip failed: $GzipError\n";

and if you want to compress each file one at a time, this will do the trick

    use strict ;
    use warnings ;
    use IO::Compress::Gzip qw(gzip $GzipError) ;

    for my $input ( glob "/my/home/*.txt" )
    {
        my $output = "$input.gz" ;
        gzip $input => $output 
            or die "Error compressing '$input': $GzipError\n";
    }


=head1 OO Interface

=head2 Constructor

The format of the constructor for C<IO::Compress::Gzip> is shown below

    my $z = new IO::Compress::Gzip $output [,OPTS]
        or die "IO::Compress::Gzip failed: $GzipError\n";

It returns an C<IO::Compress::Gzip> object on success and undef on failure. 
The variable C<$GzipError> will contain an error message on failure.

If you are running Perl 5.005 or better the object, C<$z>, returned from 
IO::Compress::Gzip can be used exactly like an L<IO::File|IO::File> filehandle. 
This means that all normal output file operations can be carried out 
with C<$z>. 
For example, to write to a compressed file/buffer you can use either of 
these forms

    $z->print("hello world\n");
    print $z "hello world\n";

The mandatory parameter C<$output> is used to control the destination
of the compressed data. This parameter can take one of these forms.

=over 5

=item A filename

If the C<$output> parameter is a simple scalar, it is assumed to be a
filename. This file will be opened for writing and the compressed data
will be written to it.

=item A filehandle

If the C<$output> parameter is a filehandle, the compressed data will be
written to it.
The string '-' can be used as an alias for standard output.


=item A scalar reference 

If C<$output> is a scalar reference, the compressed data will be stored
in C<$$output>.

=back

If the C<$output> parameter is any other type, C<IO::Compress::Gzip>::new will
return undef.

=head2 Constructor Options

C<OPTS> is any combination of the following options:

=over 5

=item C<< AutoClose => 0|1 >>

This option is only valid when the C<$output> parameter is a filehandle. If
specified, and the value is true, it will result in the C<$output> being
closed once either the C<close> method is called or the C<IO::Compress::Gzip>
object is destroyed.

This parameter defaults to 0.

=item C<< Append => 0|1 >>

Opens C<$output> in append mode. 

The behaviour of this option is dependent on the type of C<$output>.

=over 5

=item * A Buffer

If C<$output> is a buffer and C<Append> is enabled, all compressed data
will be append to the end if C<$output>. Otherwise C<$output> will be
cleared before any data is written to it.

=item * A Filename

If C<$output> is a filename and C<Append> is enabled, the file will be
opened in append mode. Otherwise the contents of the file, if any, will be
truncated before any compressed data is written to it.

=item * A Filehandle

If C<$output> is a filehandle, the file pointer will be positioned to the
end of the file via a call to C<seek> before any compressed data is written
to it.  Otherwise the file pointer will not be moved.

=back

This parameter defaults to 0.





=item C<< Merge => 0|1 >>

This option is used to compress input data and append it to an existing
compressed data stream in C<$output>. The end result is a single compressed
data stream stored in C<$output>. 



It is a fatal error to attempt to use this option when C<$output> is not an
RFC 1952 data stream.



There are a number of other limitations with the C<Merge> option:

=over 5 

=item 1

This module needs to have been built with zlib 1.2.1 or better to work. A
fatal error will be thrown if C<Merge> is used with an older version of
zlib.  

=item 2

If C<$output> is a file or a filehandle, it must be seekable.

=back


This parameter defaults to 0.



=item -Level 

Defines the compression level used by zlib. The value should either be
a number between 0 and 9 (0 means no compression and 9 is maximum
compression), or one of the symbolic constants defined below.

   Z_NO_COMPRESSION
   Z_BEST_SPEED
   Z_BEST_COMPRESSION
   Z_DEFAULT_COMPRESSION

The default is Z_DEFAULT_COMPRESSION.

Note, these constants are not imported by C<IO::Compress::Gzip> by default.

    use IO::Compress::Gzip qw(:strategy);
    use IO::Compress::Gzip qw(:constants);
    use IO::Compress::Gzip qw(:all);

=item -Strategy 

Defines the strategy used to tune the compression. Use one of the symbolic
constants defined below.

   Z_FILTERED
   Z_HUFFMAN_ONLY
   Z_RLE
   Z_FIXED
   Z_DEFAULT_STRATEGY

The default is Z_DEFAULT_STRATEGY.






=item C<< Minimal => 0|1 >>

If specified, this option will force the creation of the smallest possible
compliant gzip header (which is exactly 10 bytes long) as defined in
RFC 1952.

See the section titled "Compliance" in RFC 1952 for a definition 
of the values used for the fields in the gzip header.

All other parameters that control the content of the gzip header will
be ignored if this parameter is set to 1.

This parameter defaults to 0.

=item C<< Comment => $comment >>

Stores the contents of C<$comment> in the COMMENT field in
the gzip header.
By default, no comment field is written to the gzip file.

If the C<-Strict> option is enabled, the comment can only consist of ISO
8859-1 characters plus line feed.

If the C<-Strict> option is disabled, the comment field can contain any
character except NULL. If any null characters are present, the field
will be truncated at the first NULL.

=item C<< Name => $string >>

Stores the contents of C<$string> in the gzip NAME header field. If
C<Name> is not specified, no gzip NAME field will be created.

If the C<-Strict> option is enabled, C<$string> can only consist of ISO
8859-1 characters.

If C<-Strict> is disabled, then C<$string> can contain any character
except NULL. If any null characters are present, the field will be
truncated at the first NULL.

=item C<< Time => $number >>

Sets the MTIME field in the gzip header to $number.

This field defaults to the time the C<IO::Compress::Gzip> object was created
if this option is not specified.

=item C<< TextFlag => 0|1 >>

This parameter controls the setting of the FLG.FTEXT bit in the gzip
header. It is used to signal that the data stored in the gzip file/buffer
is probably text.

The default is 0. 

=item C<< HeaderCRC => 0|1 >>

When true this parameter will set the FLG.FHCRC bit to 1 in the gzip header
and set the CRC16 header field to the CRC of the complete gzip header
except the CRC16 field itself.

B<Note> that gzip files created with the C<HeaderCRC> flag set to 1 cannot
be read by most, if not all, of the the standard gunzip utilities, most
notably gzip version 1.2.4. You should therefore avoid using this option if
you want to maximize the portability of your gzip files.

This parameter defaults to 0.

=item C<< OS_Code => $value >>

Stores C<$value> in the gzip OS header field. A number between 0 and 255 is
valid.

If not specified, this parameter defaults to the OS code of the Operating
System this module was built on. The value 3 is used as a catch-all for all
Unix variants and unknown Operating Systems.

=item C<< ExtraField => $data >>

This parameter allows additional metadata to be stored in the ExtraField in
the gzip header. An RFC 1952 compliant ExtraField consists of zero or more
subfields. Each subfield consists of a two byte header followed by the
subfield data.

The list of subfields can be supplied in any of the following formats

    -ExtraField => [$id1, $data1,
                    $id2, $data2,
                     ...
                   ]
    -ExtraField => [ [$id1 => $data1],
                     [$id2 => $data2],
                     ...
                   ]
    -ExtraField => { $id1 => $data1,
                     $id2 => $data2,
                     ...
                   }

Where C<$id1>, C<$id2> are two byte subfield ID's. The second byte of
the ID cannot be 0, unless the C<Strict> option has been disabled.

If you use the hash syntax, you have no control over the order in which
the ExtraSubFields are stored, plus you cannot have SubFields with
duplicate ID.

Alternatively the list of subfields can by supplied as a scalar, thus

    -ExtraField => $rawdata

If you use the raw format, and the C<Strict> option is enabled,
C<IO::Compress::Gzip> will check that C<$rawdata> consists of zero or more
conformant sub-fields. When C<Strict> is disabled, C<$rawdata> can
consist of any arbitrary byte stream.

The maximum size of the Extra Field 65535 bytes.

=item C<< ExtraFlags => $value >>

Sets the XFL byte in the gzip header to C<$value>.

If this option is not present, the value stored in XFL field will be
determined by the setting of the C<Level> option.