Provided by: perl-doc_5.38.2-3.2ubuntu0.1_all 
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 = IO::Compress::Gzip->new( $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_filename_or_reference => $output_filename_or_reference [,OPTS]
or die "gzip failed: $GzipError\n";
The functional interface needs Perl5.005 or better.
gzip $input_filename_or_reference => $output_filename_or_reference [, OPTS]
"gzip" expects at least two parameters, $input_filename_or_reference and $output_filename_or_reference
and zero or more optional parameters (see "Optional Parameters")
The $input_filename_or_reference parameter
The parameter, $input_filename_or_reference, is used to define the source of the uncompressed data.
It can take one of the following forms:
A filename
If the $input_filename_or_reference 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_filename_or_reference 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_filename_or_reference is a scalar reference, the input data will be read from
$$input_filename_or_reference.
An array reference
If $input_filename_or_reference is an array reference, each element in the array must be a filename.
The input data will be read from each file in turn.
The complete array will be walked to ensure that it only contains valid filenames before any data is
compressed.
An Input FileGlob string
If $input_filename_or_reference is a string that is delimited by the characters "<" and ">" "gzip"
will assume that it is an input fileglob string. The input is the list of files that match the
fileglob.
See File::GlobMapper for more details.
If the $input_filename_or_reference parameter is any other type, "undef" will be returned.
In addition, if $input_filename_or_reference is a simple filename, the default values for the "Name" and
"Time" options will be sourced from that file.
If you do not want to use these defaults they can be overridden by explicitly setting the "Name" and
"Time" options or by setting the "Minimal" parameter.
The $output_filename_or_reference parameter
The parameter $output_filename_or_reference is used to control the destination of the compressed data.
This parameter can take one of these forms.
A filename
If the $output_filename_or_reference parameter is a simple scalar, it is assumed to be a filename.
This file will be opened for writing and the compressed data will be written to it.
A filehandle
If the $output_filename_or_reference parameter is a filehandle, the compressed data will be written
to it. The string '-' can be used as an alias for standard output.
A scalar reference
If $output_filename_or_reference is a scalar reference, the compressed data will be stored in
$$output_filename_or_reference.
An Array Reference
If $output_filename_or_reference is an array reference, the compressed data will be pushed onto the
array.
An Output FileGlob
If $output_filename_or_reference 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_filename_or_reference is an fileglob string, $input_filename_or_reference must also be
a fileglob string. Anything else is an error.
See File::GlobMapper for more details.
If the $output_filename_or_reference parameter is any other type, "undef" will be returned.
Notes
When $input_filename_or_reference maps to multiple files/buffers and $output_filename_or_reference is a
single file/buffer the input files/buffers will be stored in $output_filename_or_reference as a
concatenated series of compressed data streams.
Optional Parameters
The optional parameters for the one-shot function "gzip" are (for the most part) identical to those used
with the OO interface defined in the "Constructor Options" section. The exceptions are listed 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"
This option is now a no-op. All files will be read in binmode.
"Append => 0|1"
The behaviour of this option is dependent on the type of output data stream.
• A Buffer
If "Append" is enabled, all compressed data will be append to the end of the output buffer.
Otherwise the output buffer will be cleared before any compressed data is written to it.
• A Filename
If "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 "Append" is enabled, the filehandle 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.
When "Append" is specified, and set to true, it will append all compressed data to the output data
stream.
So when the output is a filehandle it will carry out a seek to the eof before writing any compressed
data. If the output is a filename, it will be opened for appending. If the output is a buffer, all
compressed data will be appended to the existing buffer.
Conversely when "Append" is not specified, or it is present and is set to false, it will operate as
follows.
When the output is a filename, it will truncate the contents of the file before writing any
compressed data. If the output is a filehandle its position will not be changed. If the output is a
buffer, it will be wiped before any compressed data is output.
Defaults to 0.
Examples
Here are a few example that show the capabilities of the module.
Streaming
This very simple command line example demonstrates the streaming capabilities of the module. The code
reads data from STDIN, compresses it, and writes the compressed data to STDOUT.
$ echo hello world | perl -MIO::Compress::Gzip=gzip -e 'gzip \*STDIN => \*STDOUT' >output.gz
The special filename "-" can be used as a standin for both "\*STDIN" and "\*STDOUT", so the above can be
rewritten as
$ echo hello world | perl -MIO::Compress::Gzip=gzip -e 'gzip "-" => "-"' >output.gz
Compressing a file from the filesystem
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";
Reading from a Filehandle and writing to an in-memory buffer
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 = IO::File->new( "<file1.txt" )
or die "Cannot open 'file1.txt': $!\n" ;
my $buffer ;
gzip $input => \$buffer
or die "gzip failed: $GzipError\n";
Compressing multiple files
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 = IO::Compress::Gzip->new( $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 zero or more 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
of $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 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, "fileno" will return the underlying file
descriptor. Once the "close" method is called "fileno" will return "undef".
If the $z object 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 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
EXAMPLES
Apache::GZip Revisited
See IO::Compress::FAQ
Working with Net::FTP
See IO::Compress::FAQ
SUPPORT
General feedback/questions/bug reports should be sent to <https://github.com/pmqs/IO-Copress/issues>
(preferred) or <https://rt.cpan.org/Public/Dist/Display.html?Name=IO-Copress>.
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::Lzma, IO::Uncompress::UnLzma, IO::Compress::Xz, IO::Uncompress::UnXz, IO::Compress::Lzip,
IO::Uncompress::UnLzip, IO::Compress::Lzop, IO::Uncompress::UnLzop, IO::Compress::Lzf,
IO::Uncompress::UnLzf, IO::Compress::Zstd, IO::Uncompress::UnZstd, IO::Uncompress::AnyInflate,
IO::Uncompress::AnyUncompress
IO::Compress::FAQ
File::GlobMapper, Archive::Zip, Archive::Tar, IO::Zlib
For RFC 1950, 1951 and 1952 see <https://datatracker.ietf.org/doc/html/rfc1950>,
<https://datatracker.ietf.org/doc/html/rfc1951> and <https://datatracker.ietf.org/doc/html/rfc1952>
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 the zlib-ng compression library is <https://github.com/zlib-ng/zlib-ng>.
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) 2005-2023 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 v5.38.2 2025-04-08 IO::Compress::Gzip(3perl)