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IO::Compress::Gzip(3)  Perl Programmers Reference Guide	 IO::Compress::Gzip(3)

NAME
       IO::Compress::Gzip - Write RFC 1952 files/buffers

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

	   my $status = gzip $input => $output [,OPTS]
	       or die "gzip failed: $GzipError\n";

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

	   $z->print($string);
	   $z->printf($format, $string);
	   $z->write($string);
	   $z->syswrite($string [, $length, $offset]);
	   $z->flush();
	   $z->tell();
	   $z->eof();
	   $z->seek($position, $whence);
	   $z->binmode();
	   $z->fileno();
	   $z->opened();
	   $z->autoflush();
	   $z->input_line_number();
	   $z->newStream( [OPTS] );

	   $z->deflateParams();

	   $z->close() ;

	   $GzipError ;

	   # IO::File mode

	   print $z $string;
	   printf $z $format, $string;
	   tell $z
	   eof $z
	   seek $z, $position, $whence
	   binmode $z
	   fileno $z
	   close $z ;

DESCRIPTION
       This module provides a Perl interface that allows writing compressed
       data to files or buffer as defined in RFC 1952.

       All the gzip headers defined in RFC 1952 can be created using this
       module.

       For reading RFC 1952 files/buffers, see the companion module
       IO::Uncompress::Gunzip.

Functional Interface
       A top-level function, "gzip", is provided to carry out "one-shot"
       compression between buffers and/or files. For finer control over the
       compression process, see the "OO Interface" section.

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

	   gzip $input => $output [,OPTS]
	       or die "gzip failed: $GzipError\n";

       The functional interface needs Perl5.005 or better.

       gzip $input => $output [, OPTS]

       "gzip" expects at least two parameters, $input and $output.

       The $input parameter

       The parameter, $input, is used to define the source of the uncompressed
       data.

       It can take one of the following forms:

       A filename
	    If the $input parameter is a simple scalar, it is assumed to be a
	    filename. This file will be opened for reading and the input data
	    will be read from it.

       A filehandle
	    If the $input parameter is a filehandle, the input data will be
	    read from it.  The string '-' can be used as an alias for standard
	    input.

       A scalar reference
	    If $input is a scalar reference, the input data will be read from
	    $$input.

       An array reference
	    If $input is an array reference, each element in the array must be
	    a filename.

	    The input data will be read from each file in turn.

	    The complete array will be walked to ensure that it only contains
	    valid filenames before any data is compressed.

       An Input FileGlob string
	    If $input is a string that is delimited by the characters "<" and
	    ">" "gzip" will assume that it is an input fileglob string. The
	    input is the list of files that match the fileglob.

	    If the fileglob does not match any files ...

	    See File::GlobMapper for more details.

       If the $input parameter is any other type, "undef" will be returned.

       In addition, if $input is a simple filename, the default values for the
       "Name" and "Time" options will be sourced from that file.

       If you do not want to use these defaults they can be overridden by
       explicitly setting the "Name" and "Time" options or by setting the
       "Minimal" parameter.

       The $output parameter

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

       A filename
	    If the $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.

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

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

       An Array Reference
	    If $output is an array reference, the compressed data will be
	    pushed onto the array.

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

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

       If the $output parameter is any other type, "undef" will be returned.

       Notes

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

       Optional Parameters

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

       "AutoClose => 0|1"
	    This option applies to any input or output data streams to "gzip"
	    that are filehandles.

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

	    This parameter defaults to 0.

       "BinModeIn => 0|1"
	    When reading from a file or filehandle, set "binmode" before
	    reading.

	    Defaults to 0.

       "Append => 0|1"
	    TODO

       Examples

       To read the contents of the file "file1.txt" and write the compressed
       data to the file "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, $input, and write the
       compressed data to a buffer, $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";
	   }

OO Interface
       Constructor

       The format of the constructor for "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 "IO::Compress::Gzip" object on success and undef on
       failure.	 The variable $GzipError will contain an error message on
       failure.

       If you are running Perl 5.005 or better the object, $z, returned from
       IO::Compress::Gzip can be used exactly like an IO::File filehandle.
       This means that all normal output file operations can be carried out
       with $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 $output is used to control the destination of
       the compressed data. This parameter can take one of these forms.

       A filename
	    If the $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.

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

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

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

       Constructor Options

       "OPTS" is any combination of the following options:

       "AutoClose => 0|1"
	    This option is only valid when the $output parameter is a
	    filehandle. If specified, and the value is true, it will result in
	    the $output being closed once either the "close" method is called
	    or the "IO::Compress::Gzip" object is destroyed.

	    This parameter defaults to 0.

       "Append => 0|1"
	    Opens $output in append mode.

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

	    ·	 A Buffer

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

	    ·	 A Filename

		 If $output is a filename and "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.

	    ·	 A Filehandle

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

	    This parameter defaults to 0.

       "Merge => 0|1"
	    This option is used to compress input data and append it to an
	    existing compressed data stream in $output. The end result is a
	    single compressed data stream stored in $output.

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

	    There are a number of other limitations with the "Merge" option:

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

	    2.	 If $output is a file or a filehandle, it must be seekable.

	    This parameter defaults to 0.

       -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 "IO::Compress::Gzip" by
	    default.

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

       -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.

       "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.

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

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

	    If the "-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.

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

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

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

       "Time => $number"
	    Sets the MTIME field in the gzip header to $number.

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

       "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.

       "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.

	    Note that gzip files created with the "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.

       "OS_Code => $value"
	    Stores $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.

       "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 $id1, $id2 are two byte subfield ID's. The second byte of
	    the ID cannot be 0, unless the "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 "Strict" option is enabled,
	    "IO::Compress::Gzip" will check that $rawdata consists of zero or
	    more conformant sub-fields. When "Strict" is disabled, $rawdata
	    can consist of any arbitrary byte stream.

	    The maximum size of the Extra Field 65535 bytes.

       "ExtraFlags => $value"
	    Sets the XFL byte in the gzip header to $value.

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

	    If "Level => Z_BEST_SPEED" has been specified then XFL is set to
	    2.	If "Level => Z_BEST_COMPRESSION" has been specified then XFL
	    is set to 4.  Otherwise XFL is set to 0.

       "Strict => 0|1"
	    "Strict" will optionally police the values supplied with other
	    options to ensure they are compliant with RFC1952.

	    This option is enabled by default.

	    If "Strict" is enabled the following behaviour will be policed:

	    ·	 The value supplied with the "Name" option can only contain
		 ISO 8859-1 characters.

	    ·	 The value supplied with the "Comment" option can only contain
		 ISO 8859-1 characters plus line-feed.

	    ·	 The values supplied with the "-Name" and "-Comment" options
		 cannot contain multiple embedded nulls.

	    ·	 If an "ExtraField" option is specified and it is a simple
		 scalar, it must conform to the sub-field structure as defined
		 in RFC 1952.

	    ·	 If an "ExtraField" option is specified the second byte of the
		 ID will be checked in each subfield to ensure that it does
		 not contain the reserved value 0x00.

	    When "Strict" is disabled the following behaviour will be policed:

	    ·	 The value supplied with "-Name" option can contain any
		 character except NULL.

	    ·	 The value supplied with "-Comment" option can contain any
		 character except NULL.

	    ·	 The values supplied with the "-Name" and "-Comment" options
		 can contain multiple embedded nulls. The string written to
		 the gzip header will consist of the characters up to, but not
		 including, the first embedded NULL.

	    ·	 If an "ExtraField" option is specified and it is a simple
		 scalar, the structure will not be checked. The only error is
		 if the length is too big.

	    ·	 The ID header in an "ExtraField" sub-field can consist of any
		 two bytes.

       Examples

       TODO

Methods
       print

       Usage is

	   $z->print($data)
	   print $z $data

       Compresses and outputs the contents of the $data parameter. This has
       the same behaviour as the "print" built-in.

       Returns true if successful.

       printf

       Usage is

	   $z->printf($format, $data)
	   printf $z $format, $data

       Compresses and outputs the contents of the $data parameter.

       Returns true if successful.

       syswrite

       Usage is

	   $z->syswrite $data
	   $z->syswrite $data, $length
	   $z->syswrite $data, $length, $offset

       Compresses and outputs the contents of the $data parameter.

       Returns the number of uncompressed bytes written, or "undef" if
       unsuccessful.

       write

       Usage is

	   $z->write $data
	   $z->write $data, $length
	   $z->write $data, $length, $offset

       Compresses and outputs the contents of the $data parameter.

       Returns the number of uncompressed bytes written, or "undef" if
       unsuccessful.

       flush

       Usage is

	   $z->flush;
	   $z->flush($flush_type);

       Flushes any pending compressed data to the output file/buffer.

       This method takes an optional parameter, $flush_type, that controls how
       the flushing will be carried out. By default the $flush_type used is
       "Z_FINISH". Other valid values for $flush_type are "Z_NO_FLUSH",
       "Z_SYNC_FLUSH", "Z_FULL_FLUSH" and "Z_BLOCK". It is strongly
       recommended that you only set the "flush_type" parameter if you fully
       understand the implications of what it does - overuse of "flush" can
       seriously degrade the level of compression achieved. See the "zlib"
       documentation for details.

       Returns true on success.

       tell

       Usage is

	   $z->tell()
	   tell $z

       Returns the uncompressed file offset.

       eof

       Usage is

	   $z->eof();
	   eof($z);

       Returns true if the "close" method has been called.

       seek

	   $z->seek($position, $whence);
	   seek($z, $position, $whence);

       Provides a sub-set of the "seek" functionality, with the restriction
       that it is only legal to seek forward in the output file/buffer.	 It is
       a fatal error to attempt to seek backward.

       Empty parts of the file/buffer will have NULL (0x00) bytes written to
       them.

       The $whence parameter takes one the usual values, namely SEEK_SET,
       SEEK_CUR or SEEK_END.

       Returns 1 on success, 0 on failure.

       binmode

       Usage is

	   $z->binmode
	   binmode $z ;

       This is a noop provided for completeness.

       opened

	   $z->opened()

       Returns true if the object currently refers to a opened file/buffer.

       autoflush

	   my $prev = $z->autoflush()
	   my $prev = $z->autoflush(EXPR)

       If the $z object is associated with a file or a filehandle, this method
       returns the current autoflush setting for the underlying filehandle. If
       "EXPR" is present, and is non-zero, it will enable flushing after every
       write/print operation.

       If $z is associated with a buffer, this method has no effect and always
       returns "undef".

       Note that the special variable $| cannot be used to set or retrieve the
       autoflush setting.

       input_line_number

	   $z->input_line_number()
	   $z->input_line_number(EXPR)

       This method always returns "undef" when compressing.

       fileno

	   $z->fileno()
	   fileno($z)

       If the $z object is associated with a file or a filehandle, this method
       will return the underlying file descriptor.

       If the $z object is is associated with a buffer, this method will
       return undef.

       close

	   $z->close() ;
	   close $z ;

       Flushes any pending compressed data and then closes the output
       file/buffer.

       For most versions of Perl this method will be automatically invoked if
       the IO::Compress::Gzip object is destroyed (either explicitly or by the
       variable with the reference to the object going out of scope). The
       exceptions are Perl versions 5.005 through 5.00504 and 5.8.0. In these
       cases, the "close" method will be called automatically, but not until
       global destruction of all live objects when the program is terminating.

       Therefore, if you want your scripts to be able to run on all versions
       of Perl, you should call "close" explicitly and not rely on automatic
       closing.

       Returns true on success, otherwise 0.

       If the "AutoClose" option has been enabled when the IO::Compress::Gzip
       object was created, and the object is associated with a file, the
       underlying file will also be closed.

       newStream([OPTS])

       Usage is

	   $z->newStream( [OPTS] )

       Closes the current compressed data stream and starts a new one.

       OPTS consists of any of the the options that are available when
       creating the $z object.

       See the "Constructor Options" section for more details.

       deflateParams

       Usage is

	   $z->deflateParams

       TODO

Importing
       A number of symbolic constants are required by some methods in
       "IO::Compress::Gzip". None are imported by default.

       :all Imports "gzip", $GzipError and all symbolic constants that can be
	    used by "IO::Compress::Gzip". Same as doing this

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

       :constants
	    Import all symbolic constants. Same as doing this

		use IO::Compress::Gzip qw(:flush :level :strategy) ;

       :flush
	    These symbolic constants are used by the "flush" method.

		Z_NO_FLUSH
		Z_PARTIAL_FLUSH
		Z_SYNC_FLUSH
		Z_FULL_FLUSH
		Z_FINISH
		Z_BLOCK

       :level
	    These symbolic constants are used by the "Level" option in the
	    constructor.

		Z_NO_COMPRESSION
		Z_BEST_SPEED
		Z_BEST_COMPRESSION
		Z_DEFAULT_COMPRESSION

       :strategy
	    These symbolic constants are used by the "Strategy" option in the
	    constructor.

		Z_FILTERED
		Z_HUFFMAN_ONLY
		Z_RLE
		Z_FIXED
		Z_DEFAULT_STRATEGY

       For

EXAMPLES
       TODO

SEE ALSO
       Compress::Zlib, IO::Uncompress::Gunzip, IO::Compress::Deflate,
       IO::Uncompress::Inflate, IO::Compress::RawDeflate,
       IO::Uncompress::RawInflate, IO::Compress::Bzip2,
       IO::Uncompress::Bunzip2, IO::Compress::Lzop, IO::Uncompress::UnLzop,
       IO::Compress::Lzf, IO::Uncompress::UnLzf, IO::Uncompress::AnyInflate,
       IO::Uncompress::AnyUncompress

       Compress::Zlib::FAQ

       File::GlobMapper, Archive::Zip, Archive::Tar, IO::Zlib

       For RFC 1950, 1951 and 1952 see http://www.faqs.org/rfcs/rfc1950.html,
       http://www.faqs.org/rfcs/rfc1951.html and
       http://www.faqs.org/rfcs/rfc1952.html

       The zlib compression library was written by Jean-loup Gailly
       gzip@prep.ai.mit.edu and Mark Adler madler@alumni.caltech.edu.

       The primary site for the zlib compression library is
       http://www.zlib.org.

       The primary site for gzip is http://www.gzip.org.

AUTHOR
       This module was written by Paul Marquess, pmqs@cpan.org.

MODIFICATION HISTORY
       See the Changes file.

COPYRIGHT AND LICENSE
       Copyright (c) 2005-2007 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.

perl v5.10.0			  2007-12-18		 IO::Compress::Gzip(3)
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