IO::Co...Deflate(3perl) Perl Programmers Reference GuideIO::Co...Deflate(3perl)
NAME
IO::Compress::Deflate - Write RFC 1950 files/buffers
SYNOPSIS
use IO::Compress::Deflate qw(deflate $DeflateError) ;
my $status = deflate $input => $output [,OPTS]
or die "deflate failed: $DeflateError\n";
my $z = IO::Compress::Deflate->new( $output [,OPTS] )
or die "deflate failed: $DeflateError\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() ;
$DeflateError ;
# 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 1950.
For reading RFC 1950 files/buffers, see the companion module
IO::Uncompress::Inflate.
Functional Interface
A top-level function, "deflate", 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::Deflate qw(deflate $DeflateError) ;
deflate $input_filename_or_reference => $output_filename_or_reference [,OPTS]
or die "deflate failed: $DeflateError\n";
The functional interface needs Perl5.005 or better.
deflate $input_filename_or_reference => $output_filename_or_reference [,
OPTS]
"deflate" 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 $$input_filename_or_reference.
An array reference
If $input_filename_or_reference is an array reference, each element
in the array must be a filename.
The input data will be read from each file in turn.
The complete array will be walked to ensure that it only contains
valid filenames before any data is compressed.
An Input FileGlob string
If $input_filename_or_reference is a string that is delimited by
the characters "<" and ">" "deflate" will assume that it is an
input fileglob string. The input is the list of files that match
the fileglob.
See File::GlobMapper for more details.
If the $input_filename_or_reference parameter is any other type, "undef"
will be returned.
The $output_filename_or_reference parameter
The parameter $output_filename_or_reference is used to control the
destination of the compressed data. This parameter can take one of these
forms.
A filename
If the $output_filename_or_reference parameter is a simple scalar,
it is assumed to be a filename. This file will be opened for
writing and the compressed data will be written to it.
A filehandle
If the $output_filename_or_reference parameter is a filehandle, the
compressed data will be written to it. The string '-' can be used
as an alias for standard output.
A scalar reference
If $output_filename_or_reference is a scalar reference, the
compressed data will be stored in $$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 ">" "deflate" 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 "deflate" 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
"deflate" 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 "deflate"
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.
Oneshot 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::Deflate=deflate -e 'deflate \*STDIN => \*STDOUT' >output.1950
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::Deflate=deflate -e 'deflate "-" => "-"' >output.1950
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.1950".
use strict ;
use warnings ;
use IO::Compress::Deflate qw(deflate $DeflateError) ;
my $input = "file1.txt";
deflate $input => "$input.1950"
or die "deflate failed: $DeflateError\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::Deflate qw(deflate $DeflateError) ;
use IO::File ;
my $input = IO::File->new( "<file1.txt" )
or die "Cannot open 'file1.txt': $!\n" ;
my $buffer ;
deflate $input => \$buffer
or die "deflate failed: $DeflateError\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::Deflate qw(deflate $DeflateError) ;
deflate '</my/home/*.txt>' => '<*.1950>'
or die "deflate failed: $DeflateError\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::Deflate qw(deflate $DeflateError) ;
for my $input ( glob "/my/home/*.txt" )
{
my $output = "$input.1950" ;
deflate $input => $output
or die "Error compressing '$input': $DeflateError\n";
}
OO Interface
Constructor
The format of the constructor for "IO::Compress::Deflate" is shown below
my $z = IO::Compress::Deflate->new( $output [,OPTS] )
or die "IO::Compress::Deflate failed: $DeflateError\n";
The constructor takes one mandatory parameter, $output, defined below
and zero or more "OPTS", defined in "Constructor Options".
It returns an "IO::Compress::Deflate" object on success and "undef" on
failure. The variable $DeflateError will contain an error message on
failure.
If you are running Perl 5.005 or better the object, $z, returned from
IO::Compress::Deflate 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";
Below is a simple exaple of using the OO interface to create an output
file "myfile.1950" and write some data to it.
my $filename = "myfile.1950";
my $z = IO::Compress::Deflate->new($filename)
or die "IO::Compress::Deflate failed: $DeflateError\n";
$z->print("abcde");
$z->close();
See the "Examples" for more.
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::Deflate"::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::Deflate" 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 1950 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::Deflate"
by default.
use IO::Compress::Deflate qw(:strategy);
use IO::Compress::Deflate qw(:constants);
use IO::Compress::Deflate 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.
"Strict => 0|1"
This is a placeholder option.
Examples
Streaming
This very simple command line example demonstrates the streaming
capabilities of the module. The code reads data from STDIN or all the
files given on the commandline, compresses it, and writes the compressed
data to STDOUT.
use strict ;
use warnings ;
use IO::Compress::Deflate qw(deflate $DeflateError) ;
my $z = IO::Compress::Deflate->new("-", Stream => 1)
or die "IO::Compress::Deflate failed: $DeflateError\n";
while (<>) {
$z->print("abcde");
}
$z->close();
Note the use of "-" to means "STDOUT". Alternatively you can use
"\*STDOUT".
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.1950" there are a few options
Start by creating the compression object and opening the input file
use strict ;
use warnings ;
use IO::Compress::Deflate qw(deflate $DeflateError) ;
my $input = "file1.txt";
my $z = IO::Compress::Deflate->new("file1.txt.1950")
or die "IO::Compress::Deflate failed: $DeflateError\n";
# open the input file
open my $fh, "<", "file1.txt"
or die "Cannot open file1.txt: $!\n";
# loop through the input file & write to the compressed file
while (<$fh>) {
$z->print($_);
}
# not forgetting to close the compressed file
$z->close();
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::Deflate 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::Deflate 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::Deflate". None are imported by default.
:all Imports "deflate", $DeflateError and all symbolic constants that
can be used by "IO::Compress::Deflate". Same as doing this
use IO::Compress::Deflate qw(deflate $DeflateError :constants) ;
:constants
Import all symbolic constants. Same as doing this
use IO::Compress::Deflate 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-Compress/issues> (preferred) or
<https://rt.cpan.org/Public/Dist/Display.html?Name=IO-Compress>.
SEE ALSO
Compress::Zlib, IO::Compress::Gzip, IO::Uncompress::Gunzip,
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) 2005-2024 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 v5.40.1 2026-08-30 IO::Co...Deflate(3perl)
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