IO::Un...Gunzip(3perl)

📦

version 5.44.0 · 14 versions

💖 IO::Uncompress::Gunzip 💖

okay bestie, welcome to the IO::Uncompress::Gunzip era 💅 this is the Perl Programmers Reference Guide page (the (3perl) manual-name situation) and it's all about reading RFC 1952 files/buffers. no cap. 🦋

✨ NAME ✨

IO::Uncompress::Gunzip — Read RFC 1952 files/buffers. that's the whole name vibe. 💅

🌸 SYNOPSIS 🌸

here's the code mood board, literally exactly:

use IO::Uncompress::Gunzip qw(gunzip $GunzipError) ;

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

my $z = IO::Uncompress::Gunzip->new( $input [OPTS] )
    or die "gunzip failed: $GunzipError\n";

$status = $z->read($buffer)
$status = $z->read($buffer, $length)
$status = $z->read($buffer, $length, $offset)
$line = $z->getline()
$char = $z->getc()
$char = $z->ungetc()
$char = $z->opened()

$status = $z->inflateSync()

$data = $z->trailingData()
$status = $z->nextStream()
$data = $z->getHeaderInfo()
$z->tell()
$z->seek($position, $whence)
$z->binmode()
$z->fileno()
$z->eof()
$z->close()

$GunzipError ;

# IO::File mode

<$z>
read($z, $buffer);
read($z, $buffer, $length);
read($z, $buffer, $length, $offset);
tell($z)
seek($z, $position, $whence)
binmode($z)
fileno($z)
eof($z)
close($z)

🌈 DESCRIPTION 🌈

This module provides a Perl interface that allows the reading of files/buffers that conform to RFC 1952. ✨

For writing RFC 1952 files/buffers, see the companion module IO::Compress::Gzip. that's the whole description, periodt.

🫶 Functional Interface 🫶

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

use IO::Uncompress::Gunzip qw(gunzip $GunzipError) ;

gunzip $input_filename_or_reference => $output_filename_or_reference [,OPTS]
    or die "gunzip failed: $GunzipError\n";

The functional interface needs Perl5.005 or better. fr fr.

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

"gunzip" 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 compressed 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 uncompressed.

An Input FileGlob string — If $input_filename_or_reference is a string that is delimited by the characters "<" and ">" "gunzip" 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 uncompressed 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 uncompressed data will be written to it.
A filehandle — If the $output_filename_or_reference parameter is a filehandle, the uncompressed 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 uncompressed data will be stored in $$output_filename_or_reference.
An Array Reference — If $output_filename_or_reference is an array reference, the uncompressed 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 ">" "gunzip" 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 compressed files/buffers and $output_filename_or_reference is a single file/buffer, after uncompression $output_filename_or_reference will contain a concatenation of all the uncompressed data from each of the input files/buffers. 💫

🎀 Optional Parameters 🎀

The optional parameters for the one-shot function "gunzip" 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 "gunzip" 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 "gunzip" has completed.

This parameter defaults to 0.

"BinModeOut => 0|1" — This option is now a no-op. All files will be written 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 uncompressed data will be append to the end of the output buffer. Otherwise the output buffer will be cleared before any uncompressed 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 uncompressed 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 uncompressed 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 uncompressed 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 uncompressed data. If the output is a filename, it will be opened for appending. If the output is a buffer, all uncompressed 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 uncompressed 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 uncompressed data is output.

Defaults to 0.

"MultiStream => 0|1" — If the input file/buffer contains multiple compressed data streams, this option will uncompress the whole lot as a single data stream.

Defaults to 0.

"TrailingData => $scalar" — Returns the data, if any, that is present immediately after the compressed data stream once uncompression is complete.

This option can be used when there is useful information immediately following the compressed data stream, and you don't know the length of the compressed data stream.

If the input is a buffer, "trailingData" will return everything from the end of the compressed data stream to the end of the buffer.

If the input is a filehandle, "trailingData" will return the data that is left in the filehandle input buffer once the end of the compressed data stream has been reached. You can then use the filehandle to read the rest of the input file.

Don't bother using "trailingData" if the input is a filename.

If you know the length of the compressed data stream before you start uncompressing, you can avoid having to use "trailingData" by setting the "InputLength" option.

🌟 OneShot Examples 🌟

To read the contents of the file "file1.txt.gz" and write the uncompressed data to the file "file1.txt".

use strict ;
use warnings ;
use IO::Uncompress::Gunzip qw(gunzip $GunzipError) ;

my $input = "file1.txt.gz";
my $output = "file1.txt";
gunzip $input => $output
    or die "gunzip failed: $GunzipError\n";

To read from an existing Perl filehandle, $input, and write the uncompressed data to a buffer, $buffer.

use strict ;
use warnings ;
use IO::Uncompress::Gunzip qw(gunzip $GunzipError) ;
use IO::File ;

my $input = IO::File->new( "<file1.txt.gz" )
    or die "Cannot open 'file1.txt.gz': $!\n" ;
my $buffer ;
gunzip $input => \$buffer
    or die "gunzip failed: $GunzipError\n";

To uncompress all files in the directory "/my/home" that match "*.txt.gz" and store the compressed data in the same directory

use strict ;
use warnings ;
use IO::Uncompress::Gunzip qw(gunzip $GunzipError) ;

gunzip '</my/home/*.txt.gz>' => '</my/home/#1.txt>'
    or die "gunzip failed: $GunzipError\n";

and if you want to compress each file one at a time, this will do the trick

use strict ;
use warnings ;
use IO::Uncompress::Gunzip qw(gunzip $GunzipError) ;

for my $input ( glob "/my/home/*.txt.gz" )
{
    my $output = $input;
    $output =~ s/.gz// ;
    gunzip $input => $output
        or die "Error compressing '$input': $GunzipError\n";
}

👑 OO Interface 👑

Okay bestie, now we get to the glow-up version. Same decompression, but make it object-oriented, make it serve. 🎀

✨ Constructor ✨

Here's the shape of the constructor for IO::Uncompress::Gunzip, literally:

my $z = IO::Uncompress::Gunzip->new( $input [OPTS] )
    or die "IO::Uncompress::Gunzip failed: $GunzipError\n";

So the constructor takes one mandatory parameter, $input (we get into it below 👇), plus zero or more OPTS, which are all described in "Constructor Options". Zero is a valid number of options, she's flexible like that.

Returns an IO::Uncompress::Gunzip object if it slays, and undef if it doesn't. When it doesn't, the variable $GunzipError will be holding an error message for you. 💅

Now — if you're running Perl 5.005 or better, the object $z that came back from IO::Uncompress::Gunzip can be used exactly like an IO::File filehandle. Not "similar to", not "inspired by" — exactly like one. Which means every normal input file operation works on $z. For example, to read a line from a compressed file/buffer you can do either of these:

$line = $z->getline();
$line = <$z>;

Two ways, same energy. Pick your fighter. 🥊

Here's a lil tiny example of using the OO interface to read the compressed file myfile.gz and write what's inside to stdout:

my $filename = "myfile.gz";
my $z = IO::Uncompress::Gunzip->new($filename)
    or die "IO::Uncompress::Gunzip failed: $GunzipError\n";

while (<$z>) {
    print $_;
}
$z->close();

It's giving minimal, effortless, iconic. ✨

Wanna see more? Go peek at "EXAMPLES", there's further examples in there for you.

Now — that mandatory parameter $input is what decides where the compressed data is actually coming from. It can take one of three forms:

A filename — if $input is a scalar, it gets assumed to be a filename. The file will be opened for reading, and the compressed data gets read from it.
A filehandle — if $input is a filehandle, the compressed data gets read from it. And you can use the string '-' as an alias for standard input. Cute, right?
A scalar reference — if $input is a scalar reference, the compressed data gets read from $$input. Yes, double-dollar, that's not a typo, that's just how we dereference around here. 💀

🎀 Constructor Options 🎀

First things first: the option names below are case insensitive and can optionally have a - slapped on the front. So all of these are valid, for real for real:

-AutoClose
-autoclose
AUTOCLOSE
autoclose

See? Same option, four outfits. Supermodel behaviour. 💅

OPTS is a combo of the following options:

AutoClose => 0|1 — this one is only valid when $input is a filehandle. If you set it and the value is true, the file will get closed once either the close method is called or the IO::Uncompress::Gunzip object gets destroyed. Defaults to 0.
MultiStream => 0|1 — lets multiple concatenated compressed streams be treated as one single compressed stream. Decompression stops once either the end of the file/buffer is reached, or an error shows up (premature eof, corrupt compressed data), or the end of a stream isn't immediately followed by the start of another stream. Defaults to 0.
Prime => $string — uncompresses the contents of $string before it processes the input file/buffer. This one's a lifesaver when the compressed data is embedded inside another file/data structure and there's genuinely no way to figure out where the compressed data begins without reading the first few bytes first. If that's the situation you're in, you can prime the uncompression with those bytes using this option. 🧚
Transparent => 0|1 — if this is set and the input file/buffer is not compressed data, the module will let you read it anyway. And also: if the input file/buffer does contain compressed data and there's non-compressed data sitting immediately after it, turning this on makes the module treat the whole file/buffer as a single data stream. Defaults to 1.
BlockSize => $num — when it's reading the compressed input data, IO::Uncompress::Gunzip reads it in blocks of $num bytes. Defaults to 4096.
InputLength => $size — when present, this caps the number of compressed bytes read from the input file/buffer at $size. Super useful when there's useful data sitting directly after the compressed data stream and you already know in advance the exact length of that compressed data stream. It's mostly used when reading from a filehandle — in that case, the file pointer gets left pointing at the first byte directly after the compressed data stream. Defaults to off.
Append => 0|1 — controls what the read method does with uncompressed data. If it's 1, all uncompressed data gets appended to the output parameter of the read method. If it's 0, the contents of that output parameter get overwritten by the uncompressed data. Defaults to 0.
Strict => 0|1 — controls whether those extra checks (listed below) get run during decompression. When Strict is on, the extra tests happen. When Strict is off, they don't. Defaults to off.
1. If the FHCRC bit is set in the gzip FLG header byte, the CRC16 bytes in the header must match the crc16 value of the gzip header that was actually read.
2. If the gzip header contains a name field (FNAME), it consists solely of ISO 8859-1 characters.
3. If the gzip header contains a comment field (FCOMMENT), it consists solely of ISO 8859-1 characters plus line-feed.
4. If the gzip FEXTRA header field is present, it must conform to the sub-field structure as defined in RFC 1952.
5. The CRC32 and ISIZE trailer fields must be present.
6. The value of the CRC32 field read must match the crc32 value of the uncompressed data actually contained in the gzip file.
7. The value of the ISIZE fields read must match the length of the uncompressed data actually read from the file.
ParseExtra => 0|1 — if the gzip FEXTRA header field is present and this option is set, it forces the module to check that it conforms to the sub-field structure as defined in RFC 1952. If Strict is on, this option gets automatically enabled. Defaults to 0.

🌸 heads up bestie — that last one is the one people forget about, and then Strict quietly turns it on for you and suddenly everything's stricter than you thought. iykyk.

🎀 Methods 🎀

okay bestie, this is the part where the object actually does stuff 💅 every single one of these is a real method you can call on your $z, no gatekeeping, let's go.

read

Usage is

$status = $z->read($buffer)

So what happens here: it reads a block of compressed data (and the size of that compressed block is decided by the "Buffer" option you set in the constructor, iykyk), uncompresses it, and then writes all the uncompressed goodness into $buffer. ✨

And here's the little plot twist — if the "Append" parameter was set in the constructor, the uncompressed data gets appended to $buffer. If it wasn't? Then $buffer gets straight up overwritten. no mercy. 💀

Returns the number of uncompressed bytes written to $buffer, zero if eof, or a negative number if something went wrong 😭.

read (yes, again — it's a whole other form, don't @ me)

Usage is

$status = $z->read($buffer, $length)
$status = $z->read($buffer, $length, $offset)

$status = read($z, $buffer, $length)
$status = read($z, $buffer, $length, $offset)

This one attempts to read $length bytes of uncompressed data into $buffer. 👑

The main difference between this form of the "read" method and the previous one is that this one will attempt to return exactly $length bytes. The only circumstances where it won't is if end-of-file or an IO error is encountered. periodt.

Returns the number of uncompressed bytes written to $buffer, zero if eof, or a negative number on error.

getline

Usage is

$line = $z->getline()
$line = <$z>

Reads a single line. 📖

And the way this method fully supports the variable $/ (or $INPUT_RECORD_SEPARATOR, or $RS when "English" is in use) to determine what counts as an end of line?? iconic. Paragraph mode, record mode and file slurp mode are all supported. slay.

getc

Usage is

$char = $z->getc()

Read a single character. one (1) char. that's her. 🌸

ungetc

Usage is

$char = $z->ungetc($string)

inflateSync

Usage is

$status = $z->inflateSync()

TODO. bestie they literally just wrote TODO. we respect the honesty. 🫶

getHeaderInfo

Usage is

$hdr  = $z->getHeaderInfo();
@hdrs = $z->getHeaderInfo();

This method returns either a hash reference (if you're in scalar context) or a list of hash references (if you're in array context) that contains info about each of the header fields in the compressed data stream(s). 📋

Name — The contents of the Name header field, if present. If no name is present, the value will be undef. Note this is different from a zero length name, which will return an empty string. (yes this distinction matters, do not skip it 🔥)

Comment — The contents of the Comment header field, if present. If no comment is present, the value will be undef. Note this is different from a zero length comment, which will return an empty string. 💬

tell

Usage is

$z->tell()
tell $z

Returns the uncompressed file offset. 📍

eof

Usage is

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

Returns true if the end of the compressed input stream has been reached. 🏁

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 input file/buffer.

It is a fatal error to attempt to seek backward. 🚨 no going back, we don't do that here.

And now the tea: the implementation of "seek" in this module does not provide true random access to a compressed file/buffer. It works by uncompressing data from the current offset in the file/buffer until it reaches the uncompressed offset specified in the parameters to "seek". For very small files this may be acceptable behaviour. For large files it may cause an unacceptable delay. 😭 (tl;dr — big file, big wait, it's giving buffering.)

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. literally does nothing, but she's here for the aesthetic. 💅

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. And 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". (crickets. 💀)

Note that the special variable $| can not be used to set or retrieve the autoflush setting. do not try it bestie, she will not answer.

input_line_number

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

Returns the current uncompressed line number. If "EXPR" is present it has the effect of setting the line number.

Note that setting the line number does not change the current position within the file/buffer being read. it's just a number, it doesn't move you. 🙈

The contents of $/ are used to determine what constitutes a line terminator.

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 ;

Closes the output file/buffer. 🚪

For most versions of Perl this method will be automatically invoked if the IO::Uncompress::Gunzip 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. fr fr, just call it yourself.

Returns true on success, otherwise 0.

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

nextStream

Usage is

my $status = $z->nextStream();

Skips to the next compressed data stream in the input file/buffer. And if a new compressed data stream is found, the eof marker will be cleared and $. will be reset to 0. 🦋

Returns 1 if a new stream was found, 0 if none was found, and -1 if an error was encountered.

trailingData

Usage is

my $data = $z->trailingData();

Returns the data, if any, that is present immediately after the compressed data stream once uncompression is complete. And it only makes sense to call this method once the end of the compressed data stream has been encountered. 🎀

This option can be used when there is useful information immediately following the compressed data stream, and you don't know the length of the compressed data stream.

If the input is a buffer, "trailingData" will return everything from the end of the compressed data stream to the end of the buffer.

Don't bother using "trailingData" if the input is a filename. bestie it will not help you there.

If you know the length of the compressed data stream before you start uncompressing, you can avoid having to use "trailingData" by setting the "InputLength" option in the constructor. 💡

🌈 Importing 🌈

No symbolic constants are required by IO::Uncompress::Gunzip at present. (zero. none. nada. 😌)

:all — Imports gunzip and $GunzipError. Same as doing this:

use IO::Uncompress::Gunzip qw(gunzip $GunzipError) ;

✨ EXAMPLES ✨

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::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 💜

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!! 🎉 we made it to the end — this was perl v5.44.0, dated 2026-10-17, and yes the page really is called IO::Un...Gunzip(3perl) because even the manpage system couldn't fit the whole name in the header. iconic behaviour honestly. go uncompress something 💖🦋

📦 where this page comes from

arch rolling: perl 5.44.0-1 · Artistic-1.0-Perl AND GPL-1.0-or-later
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-11-03: a language model's rewrite of the original, under its terms

IO::Un...Gunzip(3perl)

💖 IO::Uncompress::Gunzip 💖

✨ NAME ✨

🌸 SYNOPSIS 🌸

🌈 DESCRIPTION 🌈

🫶 Functional Interface 🫶

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

The $input_filename_or_reference parameter

The $output_filename_or_reference parameter

📝 Notes 📝

🎀 Optional Parameters 🎀

🌟 OneShot Examples 🌟

👑 OO Interface 👑

✨ Constructor ✨

🎀 Constructor Options 🎀

🎀 Methods 🎀

read

read (yes, again — it's a whole other form, don't @ me)

getline

getc

ungetc

inflateSync

getHeaderInfo

tell

eof

seek

binmode

opened

autoflush

input_line_number

fileno

close

nextStream

trailingData

🌈 Importing 🌈

✨ EXAMPLES ✨

Working with Net::FTP

💖 SUPPORT 💖

🫶 SEE ALSO 🫶

👑 AUTHOR 👑

🌸 MODIFICATION HISTORY 🌸

💜 COPYRIGHT AND LICENSE 💜

The `$input_filename_or_reference` parameter

The `$output_filename_or_reference` parameter