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Compress::Raw::Zlib(3)	       User Contributed Perl Documentation	   Compress::Raw::Zlib(3)

NAME
       Compress::Raw::Zlib - Low-Level Interface to zlib compression library

SYNOPSIS
	   use Compress::Raw::Zlib ;

	   ($d, $status) = new Compress::Raw::Zlib::Deflate( [OPT] ) ;
	   $status = $d->deflate($input, $output) ;
	   $status = $d->flush($output [, $flush_type]) ;
	   $d->deflateReset() ;
	   $d->deflateParams(OPTS) ;
	   $d->deflateTune(OPTS) ;
	   $d->dict_adler() ;
	   $d->crc32() ;
	   $d->adler32() ;
	   $d->total_in() ;
	   $d->total_out() ;
	   $d->msg() ;
	   $d->get_Strategy();
	   $d->get_Level();
	   $d->get_BufSize();

	   ($i, $status) = new Compress::Raw::Zlib::Inflate( [OPT] ) ;
	   $status = $i->inflate($input, $output [, $eof]) ;
	   $status = $i->inflateSync($input) ;
	   $i->inflateReset() ;
	   $i->dict_adler() ;
	   $d->crc32() ;
	   $d->adler32() ;
	   $i->total_in() ;
	   $i->total_out() ;
	   $i->msg() ;
	   $d->get_BufSize();

	   $crc = adler32($buffer [,$crc]) ;
	   $crc = crc32($buffer [,$crc]) ;

	   $crc = adler32_combine($crc1, $crc2, $len2)l
	   $crc = crc32_combine($adler1, $adler2, $len2)

	   my $version = Compress::Raw::Zlib::zlib_version();
	   my $flags = Compress::Raw::Zlib::zlibCompileFlags();

DESCRIPTION
       The Compress::Raw::Zlib module provides a Perl interface to the zlib compression library
       (see "AUTHOR" for details about where to get zlib).

Compress::Raw::Zlib::Deflate
       This section defines an interface that allows in-memory compression using the deflate
       interface provided by zlib.

       Here is a definition of the interface available:

   ($d, $status) = new Compress::Raw::Zlib::Deflate( [OPT] )
       Initialises a deflation object.

       If you are familiar with the zlib library, it combines the features of the zlib functions
       "deflateInit", "deflateInit2" and "deflateSetDictionary".

       If successful, it will return the initialised deflation object, $d and a $status of "Z_OK"
       in a list context. In scalar context it returns the deflation object, $d, only.

       If not successful, the returned deflation object, $d, will be undef and $status will hold
       the a zlib error code.

       The function optionally takes a number of named options specified as "Name => value"
       pairs. This allows individual options to be tailored without having to specify them all in
       the parameter list.

       For backward compatibility, it is also possible to pass the parameters as a reference to a
       hash containing the name=>value pairs.

       Below is a list of the valid options:

       -Level
	    Defines the compression level. Valid values are 0 through 9, "Z_NO_COMPRESSION",
	    "Z_BEST_SPEED", "Z_BEST_COMPRESSION", and "Z_DEFAULT_COMPRESSION".

	    The default is "Z_DEFAULT_COMPRESSION".

       -Method
	    Defines the compression method. The only valid value at present (and the default) is
	    "Z_DEFLATED".

       -WindowBits
	    To compress an RFC 1950 data stream, set "WindowBits" to a positive number between 8
	    and 15.

	    To compress an RFC 1951 data stream, set "WindowBits" to "-MAX_WBITS".

	    To compress an RFC 1952 data stream (i.e. gzip), set "WindowBits" to "WANT_GZIP".

	    For a definition of the meaning and valid values for "WindowBits" refer to the zlib
	    documentation for deflateInit2.

	    Defaults to "MAX_WBITS".

       -MemLevel
	    For a definition of the meaning and valid values for "MemLevel" refer to the zlib
	    documentation for deflateInit2.

	    Defaults to MAX_MEM_LEVEL.

       -Strategy
	    Defines the strategy used to tune the compression. The valid values are
	    "Z_DEFAULT_STRATEGY", "Z_FILTERED", "Z_RLE", "Z_FIXED" and "Z_HUFFMAN_ONLY".

	    The default is "Z_DEFAULT_STRATEGY".

       -Dictionary
	    When a dictionary is specified Compress::Raw::Zlib will automatically call
	    "deflateSetDictionary" directly after calling "deflateInit". The Adler32 value for
	    the dictionary can be obtained by calling the method "$d->dict_adler()".

	    The default is no dictionary.

       -Bufsize
	    Sets the initial size for the output buffer used by the "$d->deflate" and "$d->flush"
	    methods. If the buffer has to be reallocated to increase the size, it will grow in
	    increments of "Bufsize".

	    The default buffer size is 4096.

       -AppendOutput
	    This option controls how data is written to the output buffer by the "$d->deflate"
	    and "$d->flush" methods.

	    If the "AppendOutput" option is set to false, the output buffers in the "$d->deflate"
	    and "$d->flush"  methods will be truncated before uncompressed data is written to
	    them.

	    If the option is set to true, uncompressed data will be appended to the output buffer
	    in the "$d->deflate" and "$d->flush" methods.

	    This option defaults to false.

       -CRC32
	    If set to true, a crc32 checksum of the uncompressed data will be calculated. Use the
	    "$d->crc32" method to retrieve this value.

	    This option defaults to false.

       -ADLER32
	    If set to true, an adler32 checksum of the uncompressed data will be calculated. Use
	    the "$d->adler32" method to retrieve this value.

	    This option defaults to false.

       Here is an example of using the "Compress::Raw::Zlib::Deflate" optional parameter list to
       override the default buffer size and compression level. All other options will take their
       default values.

	   my $d = new Compress::Raw::Zlib::Deflate ( -Bufsize => 300,
						      -Level   => Z_BEST_SPEED ) ;

   $status = $d->deflate($input, $output)
       Deflates the contents of $input and writes the compressed data to $output.

       The $input and $output parameters can be either scalars or scalar references.

       When finished, $input will be completely processed (assuming there were no errors). If the
       deflation was successful it writes the deflated data to $output and returns a status value
       of "Z_OK".

       On error, it returns a zlib error code.

       If the "AppendOutput" option is set to true in the constructor for the $d object, the
       compressed data will be appended to $output. If it is false, $output will be truncated
       before any compressed data is written to it.

       Note: This method will not necessarily write compressed data to $output every time it is
       called. So do not assume that there has been an error if the contents of $output is empty
       on returning from this method. As long as the return code from the method is "Z_OK", the
       deflate has succeeded.

   $status = $d->flush($output [, $flush_type])
       Typically used to finish the deflation. Any pending output will be written to $output.

       Returns "Z_OK" if successful.

       Note that flushing can seriously degrade the compression ratio, so it should only be used
       to terminate a decompression (using "Z_FINISH") or when you want to create a full flush
       point (using "Z_FULL_FLUSH").

       By default the "flush_type" used is "Z_FINISH". Other valid values for "flush_type" are
       "Z_NO_FLUSH", "Z_PARTIAL_FLUSH", "Z_SYNC_FLUSH" and "Z_FULL_FLUSH". It is strongly
       recommended that you only set the "flush_type" parameter if you fully understand the
       implications of what it does. See the "zlib" documentation for details.

       If the "AppendOutput" option is set to true in the constructor for the $d object, the
       compressed data will be appended to $output. If it is false, $output will be truncated
       before any compressed data is written to it.

   $status = $d->deflateReset()
       This method will reset the deflation object $d. It can be used when you are compressing
       multiple data streams and want to use the same object to compress each of them. It should
       only be used once the previous data stream has been flushed successfully, i.e. a call to
       "$d->flush(Z_FINISH)" has returned "Z_OK".

       Returns "Z_OK" if successful.

   $status = $d->deflateParams([OPT])
       Change settings for the deflate object $d.

       The list of the valid options is shown below. Options not specified will remain unchanged.

       -Level
	    Defines the compression level. Valid values are 0 through 9, "Z_NO_COMPRESSION",
	    "Z_BEST_SPEED", "Z_BEST_COMPRESSION", and "Z_DEFAULT_COMPRESSION".

       -Strategy
	    Defines the strategy used to tune the compression. The valid values are
	    "Z_DEFAULT_STRATEGY", "Z_FILTERED" and "Z_HUFFMAN_ONLY".

       -BufSize
	    Sets the initial size for the output buffer used by the "$d->deflate" and "$d->flush"
	    methods. If the buffer has to be reallocated to increase the size, it will grow in
	    increments of "Bufsize".

   $status = $d->deflateTune($good_length, $max_lazy, $nice_length, $max_chain)
       Tune the internal settings for the deflate object $d. This option is only available if you
       are running zlib 1.2.2.3 or better.

       Refer to the documentation in zlib.h for instructions on how to fly "deflateTune".

   $d->dict_adler()
       Returns the adler32 value for the dictionary.

   $d->crc32()
       Returns the crc32 value for the uncompressed data to date.

       If the "CRC32" option is not enabled in the constructor for this object, this method will
       always return 0;

   $d->adler32()
       Returns the adler32 value for the uncompressed data to date.

   $d->msg()
       Returns the last error message generated by zlib.

   $d->total_in()
       Returns the total number of bytes uncompressed bytes input to deflate.

   $d->total_out()
       Returns the total number of compressed bytes output from deflate.

   $d->get_Strategy()
       Returns the deflation strategy currently used. Valid values are "Z_DEFAULT_STRATEGY",
       "Z_FILTERED" and "Z_HUFFMAN_ONLY".

   $d->get_Level()
       Returns the compression level being used.

   $d->get_BufSize()
       Returns the buffer size used to carry out the compression.

   Example
       Here is a trivial example of using "deflate". It simply reads standard input, deflates it
       and writes it to standard output.

	   use strict ;
	   use warnings ;

	   use Compress::Raw::Zlib ;

	   binmode STDIN;
	   binmode STDOUT;
	   my $x = new Compress::Raw::Zlib::Deflate
	      or die "Cannot create a deflation stream\n" ;

	   my ($output, $status) ;
	   while (<>)
	   {
	       $status = $x->deflate($_, $output) ;

	       $status == Z_OK
		   or die "deflation failed\n" ;

	       print $output ;
	   }

	   $status = $x->flush($output) ;

	   $status == Z_OK
	       or die "deflation failed\n" ;

	   print $output ;

Compress::Raw::Zlib::Inflate
       This section defines an interface that allows in-memory uncompression using the inflate
       interface provided by zlib.

       Here is a definition of the interface:

    ($i, $status) = new Compress::Raw::Zlib::Inflate( [OPT] )
       Initialises an inflation object.

       In a list context it returns the inflation object, $i, and the zlib status code ($status).
       In a scalar context it returns the inflation object only.

       If successful, $i will hold the inflation object and $status will be "Z_OK".

       If not successful, $i will be undef and $status will hold the zlib error code.

       The function optionally takes a number of named options specified as "-Name => value"
       pairs. This allows individual options to be tailored without having to specify them all in
       the parameter list.

       For backward compatibility, it is also possible to pass the parameters as a reference to a
       hash containing the "name=>value" pairs.

       Here is a list of the valid options:

       -WindowBits
	    To uncompress an RFC 1950 data stream, set "WindowBits" to a positive number between
	    8 and 15.

	    To uncompress an RFC 1951 data stream, set "WindowBits" to "-MAX_WBITS".

	    To uncompress an RFC 1952 data stream (i.e. gzip), set "WindowBits" to "WANT_GZIP".

	    To auto-detect and uncompress an RFC 1950 or RFC 1952 data stream (i.e.  gzip), set
	    "WindowBits" to "WANT_GZIP_OR_ZLIB".

	    For a full definition of the meaning and valid values for "WindowBits" refer to the
	    zlib documentation for inflateInit2.

	    Defaults to "MAX_WBITS".

       -Bufsize
	    Sets the initial size for the output buffer used by the "$i->inflate" method. If the
	    output buffer in this method has to be reallocated to increase the size, it will grow
	    in increments of "Bufsize".

	    Default is 4096.

       -Dictionary
	    The default is no dictionary.

       -AppendOutput
	    This option controls how data is written to the output buffer by the "$i->inflate"
	    method.

	    If the option is set to false, the output buffer in the "$i->inflate" method will be
	    truncated before uncompressed data is written to it.

	    If the option is set to true, uncompressed data will be appended to the output buffer
	    by the "$i->inflate" method.

	    This option defaults to false.

       -CRC32
	    If set to true, a crc32 checksum of the uncompressed data will be calculated. Use the
	    "$i->crc32" method to retrieve this value.

	    This option defaults to false.

       -ADLER32
	    If set to true, an adler32 checksum of the uncompressed data will be calculated. Use
	    the "$i->adler32" method to retrieve this value.

	    This option defaults to false.

       -ConsumeInput
	    If set to true, this option will remove compressed data from the input buffer of the
	    "$i->inflate" method as the inflate progresses.

	    This option can be useful when you are processing compressed data that is embedded in
	    another file/buffer. In this case the data that immediately follows the compressed
	    stream will be left in the input buffer.

	    This option defaults to true.

       -LimitOutput
	    The "LimitOutput" option changes the behavior of the "$i->inflate" method so that the
	    amount of memory used by the output buffer can be limited.

	    When "LimitOutput" is used the size of the output buffer used will either be the
	    value of the "Bufsize" option or the amount of memory already allocated to $output,
	    whichever is larger. Predicting the output size available is tricky, so don't rely on
	    getting an exact output buffer size.

	    When "LimitOutout" is not specified "$i->inflate" will use as much memory as it takes
	    to write all the uncompressed data it creates by uncompressing the input buffer.

	    If "LimitOutput" is enabled, the "ConsumeInput" option will also be enabled.

	    This option defaults to false.

	    See "The LimitOutput option" for a discussion on why "LimitOutput" is needed and how
	    to use it.

       Here is an example of using an optional parameter to override the default buffer size.

	   my ($i, $status) = new Compress::Raw::Zlib::Inflate( -Bufsize => 300 ) ;

    $status = $i->inflate($input, $output [,$eof])
       Inflates the complete contents of $input and writes the uncompressed data to $output. The
       $input and $output parameters can either be scalars or scalar references.

       Returns "Z_OK" if successful and "Z_STREAM_END" if the end of the compressed data has been
       successfully reached.

       If not successful $status will hold the zlib error code.

       If the "ConsumeInput" option has been set to true when the "Compress::Raw::Zlib::Inflate"
       object is created, the $input parameter is modified by "inflate". On completion it will
       contain what remains of the input buffer after inflation. In practice, this means that
       when the return status is "Z_OK" the $input parameter will contain an empty string, and
       when the return status is "Z_STREAM_END" the $input parameter will contains what (if
       anything) was stored in the input buffer after the deflated data stream.

       This feature is useful when processing a file format that encapsulates a compressed data
       stream (e.g. gzip, zip) and there is useful data immediately after the deflation stream.

       If the "AppendOutput" option is set to true in the constructor for this object, the
       uncompressed data will be appended to $output. If it is false, $output will be truncated
       before any uncompressed data is written to it.

       The $eof parameter needs a bit of explanation.

       Prior to version 1.2.0, zlib assumed that there was at least one trailing byte immediately
       after the compressed data stream when it was carrying out decompression. This normally
       isn't a problem because the majority of zlib applications guarantee that there will be
       data directly after the compressed data stream.	For example, both gzip (RFC 1950) and zip
       both define trailing data that follows the compressed data stream.

       The $eof parameter only needs to be used if all of the following conditions apply

       1.   You are either using a copy of zlib that is older than version 1.2.0 or you want your
	    application code to be able to run with as many different versions of zlib as
	    possible.

       2.   You have set the "WindowBits" parameter to "-MAX_WBITS" in the constructor for this
	    object, i.e. you are uncompressing a raw deflated data stream (RFC 1951).

       3.   There is no data immediately after the compressed data stream.

       If all of these are the case, then you need to set the $eof parameter to true on the final
       call (and only the final call) to "$i->inflate".

       If you have built this module with zlib >= 1.2.0, the $eof parameter is ignored. You can
       still set it if you want, but it won't be used behind the scenes.

   $status = $i->inflateSync($input)
       This method can be used to attempt to recover good data from a compressed data stream that
       is partially corrupt.  It scans $input until it reaches either a full flush point or the
       end of the buffer.

       If a full flush point is found, "Z_OK" is returned and $input will be have all data up to
       the flush point removed. This data can then be passed to the "$i->inflate" method to be
       uncompressed.

       Any other return code means that a flush point was not found. If more data is available,
       "inflateSync" can be called repeatedly with more compressed data until the flush point is
       found.

       Note full flush points are not present by default in compressed data streams. They must
       have been added explicitly when the data stream was created by calling
       "Compress::Deflate::flush"  with "Z_FULL_FLUSH".

   $status = $i->inflateReset()
       This method will reset the inflation object $i. It can be used when you are uncompressing
       multiple data streams and want to use the same object to uncompress each of them.

       Returns "Z_OK" if successful.

   $i->dict_adler()
       Returns the adler32 value for the dictionary.

   $i->crc32()
       Returns the crc32 value for the uncompressed data to date.

       If the "CRC32" option is not enabled in the constructor for this object, this method will
       always return 0;

   $i->adler32()
       Returns the adler32 value for the uncompressed data to date.

       If the "ADLER32" option is not enabled in the constructor for this object, this method
       will always return 0;

   $i->msg()
       Returns the last error message generated by zlib.

   $i->total_in()
       Returns the total number of bytes compressed bytes input to inflate.

   $i->total_out()
       Returns the total number of uncompressed bytes output from inflate.

   $d->get_BufSize()
       Returns the buffer size used to carry out the decompression.

   Examples
       Here is an example of using "inflate".

	   use strict ;
	   use warnings ;

	   use Compress::Raw::Zlib;

	   my $x = new Compress::Raw::Zlib::Inflate()
	      or die "Cannot create a inflation stream\n" ;

	   my $input = '' ;
	   binmode STDIN;
	   binmode STDOUT;

	   my ($output, $status) ;
	   while (read(STDIN, $input, 4096))
	   {
	       $status = $x->inflate($input, $output) ;

	       print $output ;

	       last if $status != Z_OK ;
	   }

	   die "inflation failed\n"
	       unless $status == Z_STREAM_END ;

       The next example show how to use the "LimitOutput" option. Notice the use of two nested
       loops in this case. The outer loop reads the data from the input source - STDIN and the
       inner loop repeatedly calls "inflate" until $input is exhausted, we get an error, or the
       end of the stream is reached. One point worth remembering is by using the "LimitOutput"
       option you also get "ConsumeInput" set as well - this makes the code below much simpler.

	   use strict ;
	   use warnings ;

	   use Compress::Raw::Zlib;

	   my $x = new Compress::Raw::Zlib::Inflate(LimitOutput => 1)
	      or die "Cannot create a inflation stream\n" ;

	   my $input = '' ;
	   binmode STDIN;
	   binmode STDOUT;

	   my ($output, $status) ;

	 OUTER:
	   while (read(STDIN, $input, 4096))
	   {
	       do
	       {
		   $status = $x->inflate($input, $output) ;

		   print $output ;

		   last OUTER
		       unless $status == Z_OK || $status == Z_BUF_ERROR ;
	       }
	       while ($status == Z_OK && length $input);
	   }

	   die "inflation failed\n"
	       unless $status == Z_STREAM_END ;

CHECKSUM FUNCTIONS
       Two functions are provided by zlib to calculate checksums. For the Perl interface, the
       order of the two parameters in both functions has been reversed. This allows both running
       checksums and one off calculations to be done.

	   $crc = adler32($buffer [,$crc]) ;
	   $crc = crc32($buffer [,$crc]) ;

       The buffer parameters can either be a scalar or a scalar reference.

       If the $crc parameters is "undef", the crc value will be reset.

       If you have built this module with zlib 1.2.3 or better, two more CRC-related functions
       are available.

	   $crc = adler32_combine($crc1, $crc2, $len2)l
	   $crc = crc32_combine($adler1, $adler2, $len2)

       These functions allow checksums to be merged.

Misc
   my $version = Compress::Raw::Zlib::zlib_version();
       Returns the version of the zlib library.

   my $flags = Compress::Raw::Zlib::zlibCompileFlags();
       Returns the flags indicating compile-time options that were used to build the zlib
       library. See the zlib documentation for a description of the flags returned by
       "zlibCompileFlags".

       Note that when the zlib sources are built along with this module the "sprintf" flags (bits
       24, 25 and 26) should be ignored.

       If you are using zlib 1.2.0 or older, "zlibCompileFlags" will return 0.

The LimitOutput option.
       By default "$i->inflate($input, $output)" will uncompress all data in $input and write all
       of the uncompressed data it has generated to $output. This makes the interface to
       "inflate" much simpler - if the method has uncompressed $input successfully all compressed
       data in $input will have been dealt with. So if you are reading from an input source and
       uncompressing as you go the code will look something like this

	   use strict ;
	   use warnings ;

	   use Compress::Raw::Zlib;

	   my $x = new Compress::Raw::Zlib::Inflate()
	      or die "Cannot create a inflation stream\n" ;

	   my $input = '' ;

	   my ($output, $status) ;
	   while (read(STDIN, $input, 4096))
	   {
	       $status = $x->inflate($input, $output) ;

	       print $output ;

	       last if $status != Z_OK ;
	   }

	   die "inflation failed\n"
	       unless $status == Z_STREAM_END ;

       The points to note are

       o    The main processing loop in the code handles reading of compressed data from STDIN.

       o    The status code returned from "inflate" will only trigger termination of the main
	    processing loop if it isn't "Z_OK". When "LimitOutput" has not been used the "Z_OK"
	    status means means that the end of the compressed data stream has been reached or
	    there has been an error in uncompression.

       o    After the call to "inflate" all of the uncompressed data in $input will have been
	    processed. This means the subsequent call to "read" can overwrite it's contents
	    without any problem.

       For most use-cases the behavior described above is acceptable (this module and it's
       predecessor, "Compress::Zlib", have used it for over 10 years without an issue), but in a
       few very specific use-cases the amount of memory required for $output can prohibitively
       large. For example, if the compressed data stream contains the same pattern repeated
       thousands of times, a relatively small compressed data stream can uncompress into hundreds
       of megabytes.  Remember "inflate" will keep allocating memory until all the uncompressed
       data has been written to the output buffer - the size of $output is unbounded.

       The "LimitOutput" option is designed to help with this use-case.

       The main difference in your code when using "LimitOutput" is having to deal with cases
       where the $input parameter still contains some uncompressed data that "inflate" hasn't
       processed yet. The status code returned from "inflate" will be "Z_OK" if uncompression
       took place and "Z_BUF_ERROR" if the output buffer is full.

       Below is typical code that shows how to use "LimitOutput".

	   use strict ;
	   use warnings ;

	   use Compress::Raw::Zlib;

	   my $x = new Compress::Raw::Zlib::Inflate(LimitOutput => 1)
	      or die "Cannot create a inflation stream\n" ;

	   my $input = '' ;
	   binmode STDIN;
	   binmode STDOUT;

	   my ($output, $status) ;

	 OUTER:
	   while (read(STDIN, $input, 4096))
	   {
	       do
	       {
		   $status = $x->inflate($input, $output) ;

		   print $output ;

		   last OUTER
		       unless $status == Z_OK || $status == Z_BUF_ERROR ;
	       }
	       while ($status == Z_OK && length $input);
	   }

	   die "inflation failed\n"
	       unless $status == Z_STREAM_END ;

       Points to note this time:

       o    There are now two nested loops in the code: the outer loop for reading the compressed
	    data from STDIN, as before; and the inner loop to carry out the uncompression.

       o    There are two exit points from the inner uncompression loop.

	    Firstly when "inflate" has returned a status other than "Z_OK" or "Z_BUF_ERROR".
	    This means that either the end of the compressed data stream has been reached
	    ("Z_STREAM_END") or there is an error in the compressed data. In either of these
	    cases there is no point in continuing with reading the compressed data, so both loops
	    are terminated.

	    The second exit point tests if there is any data left in the input buffer, $input -
	    remember that the "ConsumeInput" option is automatically enabled when "LimitOutput"
	    is used.  When the input buffer has been exhausted, the outer loop can run again and
	    overwrite a now empty $input.

ACCESSING ZIP FILES
       Although it is possible (with some effort on your part) to use this module to access .zip
       files, there are other perl modules available that will do all the hard work for you.
       Check out "Archive::Zip", "Archive::Zip::SimpleZip", "IO::Compress::Zip" and
       "IO::Uncompress::Unzip".

FAQ
   Compatibility with Unix compress/uncompress.
       This module is not compatible with Unix "compress".

       If you have the "uncompress" program available, you can use this to read compressed files

	   open F, "uncompress -c $filename |";
	   while (<F>)
	   {
	       ...

       Alternatively, if you have the "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 "compress" program available

	   open F, "| compress -c $filename ";
	   print F "data";
	   ...
	   close F ;

   Accessing .tar.Z files
       See previous FAQ item.

       If the "Archive::Tar" module is installed and either the "uncompress" or "gunzip" programs
       are available, you can use one of these workarounds to read ".tar.Z" files.

       Firstly with "uncompress"

	   use strict;
	   use warnings;
	   use Archive::Tar;

	   open F, "uncompress -c $filename |";
	   my $tar = Archive::Tar->new(*F);
	   ...

       and this with "gunzip"

	   use strict;
	   use warnings;
	   use Archive::Tar;

	   open F, "gunzip -c $filename |";
	   my $tar = Archive::Tar->new(*F);
	   ...

       Similarly, if the "compress" program is available, you can use this to write a ".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 ;

   Zlib Library Version Support
       By default "Compress::Raw::Zlib" will build with a private copy of version 1.2.5 of the
       zlib library. (See the README file for details of how to override this behaviour)

       If you decide to use a different version of the zlib library, you need to be aware of the
       following issues

       o    First off, you must have zlib 1.0.5 or better.

       o    You need to have zlib 1.2.1 or better if you want to use the "-Merge" option with
	    "IO::Compress::Gzip", "IO::Compress::Deflate" and "IO::Compress::RawDeflate".

CONSTANTS
       All the zlib constants are automatically imported when you make use of
       Compress::Raw::Zlib.

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

       IO::Compress::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) 2005-2013 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 v5.16.3				    2013-05-19			   Compress::Raw::Zlib(3)
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