IO::COMPRESS::DEFLATE(3pm)

📦

version 5.42.3 · 17 versions

okay so bestie, this is the manual page for IO::Compress::Deflate(3pm) — yes it’s giving Perl compression royalty, and we’re about to read it together. 💅✨

✨ NAME ✨

IO::Compress::Deflate — write RFC 1950 files/buffers. Periodt. 🎀

🫶 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 gives you a Perl interface that lets you write compressed data to files or buffer, exactly as RFC 1950 defines it. 🔥

For reading RFC 1950 files/buffers, see the companion module IO::Uncompress::Inflate.

🧚 Functional Interface

Bestie, there’s a top-level function called deflate that does “one-shot” compression between buffers and/or files. If you want finer control over the compression process, go 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. no cap.

🎀 `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, plus zero or more optional parameters (peep “Optional Parameters”). 👀

The $input_filename_or_reference parameter

This parameter defines where the uncompressed data comes from. It can take one of these forms:

A filename — if $input_filename_or_reference is a simple scalar, it’s assumed to be a filename. That file gets opened for reading, and the input data is read from it. 📂
A filehandle — if $input_filename_or_reference is a filehandle, the input data is 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 is read from $$input_filename_or_reference. 🪞
An array reference — if $input_filename_or_reference is an array reference, every element in the array must be a filename. The input data is read from each file in turn. The complete array will be walked to make sure it only contains valid filenames before any data is compressed. 🧚
An Input FileGlob string — if $input_filename_or_reference is a string delimited by < and >, deflate assumes it’s 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 controls where the compressed data goes. It can take one of these forms:

A filename — if $output_filename_or_reference is a simple scalar, it’s assumed to be a filename. That file gets opened for writing, and the compressed data is written to it. 📝
A filehandle — if $output_filename_or_reference is a filehandle, the compressed data is 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 is stored in $$output_filename_or_reference. 🪞
An Array Reference — if $output_filename_or_reference is an array reference, the compressed data is pushed onto the array. 📚
An Output FileGlob — if $output_filename_or_reference is a string delimited by < and >, deflate assumes it’s an output fileglob string. The output is the list of files that match the fileglob. When $output_filename_or_reference is a 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 — ok so 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 appended 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 examples 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 💅

okay so now we’re doing the OO interface, and it’s lowkey the main character energy of this module. The format of the constructor for IO::Compress::Deflate is literally this:

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, plus 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 example 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 section 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 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 $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:

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.
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 💅

okay bestie, this is where we actually use the $z object. every method, every return value, every little caveat — no skipped lore. ✨

💖 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. slay.

🌸 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.

bestie, real talk: 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

Usage is

$z->seek($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 of 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

Usage is

$z->opened()

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

🍓 autoflush

Usage is

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

Usage is

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

This method always returns undef when compressing.

🦋 fileno

Usage is

$z->fileno()
fileno($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

Usage is

$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. periodt.

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

not me leaving this exactly as TODO — that's what the page says, bestie, i don't make the rules. 🙈

🌈 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 👑

The whole ✨friend group✨ is here:

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

Also:

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 🌸

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

✨ and that's the whole page, bestie — source/version perl v5.42.3, dated 2026-11-03, page IO::Com...:Deflate(3pm). go forth and compress responsibly 💖

📦 where this page comes from

alpine 3.24: perl-doc 5.42.3-r0 · Artistic-1.0-Perl OR GPL-1.0-or-later
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-04: a language model's rewrite of the original, under its terms

IO::COMPRESS::DEFLATE(3pm)

✨ NAME ✨

🫶 SYNOPSIS 🫶

💖 DESCRIPTION 💖

🧚 Functional Interface

🎀 deflate $input_filename_or_reference => $output_filename_or_reference [, OPTS] 🎀

🌈 Oneshot Examples 🌈

💅 OO Interface 💅

🌸 Constructor Options 🌸

🎀 Examples 🎀

🌈 Streaming 🌈

🦋 Compressing a file from the filesystem 🦋

💅 Methods 💅

💖 print

🌸 printf

🦋 syswrite

🎀 write

🔥 flush

⭐ tell

🫶 eof

🌈 seek

🧚 binmode

👑 opened

🍓 autoflush

💜 input_line_number

🦋 fileno

💀 close

🆕 newStream([OPTS])

🙈 deflateParams

🌈 Importing 🌈

:all

:constants

:flush

:level

:strategy

🎀 EXAMPLES 🎀

Apache::GZip Revisited

Working with Net::FTP

🫶 SUPPORT 🫶

👑 SEE ALSO 👑

💜 AUTHOR 💜

🦋 MODIFICATION HISTORY 🦋

🌸 COPYRIGHT AND LICENSE 🌸

🎀 `deflate $input_filename_or_reference => $output_filename_or_reference [, OPTS]` 🎀