info > IO::Uncompress::Gunzip

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📘 NAME

IO::Uncompress::Gunzip - Read RFC 1952 files/buffers

🚀 Quick Reference

Use Case	Command	Description
Uncompress a .gz file to a file	gunzip 'file1.txt.gz' => 'file1.txt'	One-shot decompression of a gzip file
Uncompress from a filehandle to a buffer	gunzip $input => \$buffer	Read from an open filehandle, store output in scalar
Uncompress multiple files with glob	gunzip '</my/home/*.txt.gz>' => '</my/home/#1.txt>'	Bulk decompress using File::GlobMapper
OO: create a new gunzip reader object	my $z = IO::Uncompress::Gunzip->new($input);	Object-oriented interface for fine-grained control
OO: read a line	$line = $z->getline();	Read one line from uncompressed data
OO: read a block of data	$status = $z->read($buffer);	Read uncompressed data into buffer

📋 SYNOPSIS

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.

⚙️ 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.

📌 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 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 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 the parameter 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 the parameter is a string 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 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. It can take one of these forms:

• 📄 A filename — If the 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 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 the parameter is a scalar reference, the uncompressed data will be stored in $$output_filename_or_reference.
• 📚 An Array Reference — If the parameter is an array reference, the uncompressed data will be pushed onto the array.
• 🌐 An Output FileGlob — If the parameter is a string 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 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 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. 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 appended 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.

💡 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

🏗️ Constructor

The format of the constructor for IO::Uncompress::Gunzip is shown below

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

Returns an IO::Uncompress::Gunzip object on success and undef on failure. The variable $GunzipError will contain an error message on failure.

If you are running Perl 5.005 or better the object, $z, returned from IO::Uncompress::Gunzip can be used exactly like an IO::File filehandle. This means that all normal input file operations can be carried out with $z. For example, to read a line from a compressed file/buffer you can use either of these forms

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

The mandatory parameter $input is used to determine the source of the compressed data. This parameter can take one of three forms.

• 📄 A filename — If the $input parameter is a scalar, it is assumed to be a filename. This file will be opened for reading and the compressed data will be read from it.
• 🔗 A filehandle — If the $input parameter is a filehandle, the compressed data will be read from it. The string '-' can be used as an alias for standard input.
• 📦 A scalar reference — If $input is a scalar reference, the compressed data will be read from $$input.

⚙️ Constructor Options

The option names defined below are case insensitive and can be optionally prefixed by a '-'. So all of the following are valid

-AutoClose
-autoclose
AUTOCLOSE
autoclose

OPTS is a combination of the following options:

• AutoClose => 0|1 — This option is only valid when the $input parameter is a filehandle. If specified, and the value is true, it will result in the file being closed once either the close method is called or the IO::Uncompress::Gunzip object is destroyed. Defaults to 0.
• MultiStream => 0|1 — Allows multiple concatenated compressed streams to be treated as a single compressed stream. Decompression will stop once either the end of the file/buffer is reached, an error is encountered (premature eof, corrupt compressed data) or the end of a stream is not immediately followed by the start of another stream. Defaults to 0.
• Prime => $string — This option will uncompress the contents of $string before processing the input file/buffer. This option can be useful when the compressed data is embedded in another file/data structure and it is not possible to work out where the compressed data begins without having to read the first few bytes. If this is the case, the uncompression can be primed with these bytes using this option.
• Transparent => 0|1 — If this option is set and the input file/buffer is not compressed data, the module will allow reading of it anyway. In addition, if the input file/buffer does contain compressed data and there is non-compressed data immediately following it, setting this option will make this module treat the whole file/buffer as a single data stream. Defaults to 1.
• BlockSize => $num — When reading the compressed input data, IO::Uncompress::Gunzip will read it in blocks of $num bytes. Defaults to 4096.
• InputLength => $size — When present this option will limit the number of compressed bytes read from the input file/buffer to $size. This option can be used in the situation where there is useful data directly after the compressed data stream and you know beforehand the exact length of the compressed data stream. This option is mostly used when reading from a filehandle, in which case the file pointer will be left pointing to the first byte directly after the compressed data stream. Defaults to off.
• Append => 0|1 — This option controls what the read method does with uncompressed data. If set to 1, all uncompressed data will be appended to the output parameter of the read method. If set to 0, the contents of the output parameter of the read method will be overwritten by the uncompressed data. Defaults to 0.
• Strict => 0|1 — This option controls whether the extra checks defined below are used when carrying out the decompression. When Strict is on, the extra tests are carried out, when Strict is off they are not. The default for this option is 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 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 will force the module to check that it conforms to the sub-field structure as defined in RFC 1952. If the Strict is on it will automatically enable this option. Defaults to 0.

💡 Examples (OO)

TODO

🛠️ Methods

read

Usage is

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

Reads a block of compressed data (the size of the compressed block is determined by the Buffer option in the constructor), uncompresses it and writes any uncompressed data into $buffer. If the Append parameter is set in the constructor, the uncompressed data will be appended to the $buffer parameter. Otherwise $buffer will be overwritten. Returns the number of uncompressed bytes written to $buffer, zero if eof or a negative number on error.

read (with length/offset)

Usage is

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

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

Attempt 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 that this function will not is if end-of-file or an IO error is encountered. 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. This method fully supports the use of the variable $/ (or $INPUT_RECORD_SEPARATOR or $RS when "English" is in use) to determine what constitutes an end of line. Paragraph mode, record mode and file slurp mode are all supported.

getc

Usage is

$char = $z->getc()

Read a single character.

ungetc

Usage is

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

inflateSync

Usage is

$status = $z->inflateSync()

TODO

getHeaderInfo

Usage is

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

This method returns either a hash reference (in scalar context) or a list or hash references (in array context) that contains information 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.
• 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. Note that 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. 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)

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. 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. 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. 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. 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. 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 in the constructor.

📦 Importing

No symbolic constants are required by IO::Uncompress::Gunzip at present.

• :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 http://www.faqs.org/rfcs/rfc1950.html, http://www.faqs.org/rfcs/rfc1951.html and http://www.faqs.org/rfcs/rfc1952.html

The zlib compression library was written by Jean-loup Gailly gzip@prep.edu and Mark Adler madler@alumni.edu.

The primary site for the zlib compression library is http://www.zlib.org.

The primary site for gzip is http://www.gzip.org.

✍️ AUTHOR

This module was written by Paul Marquess, pmqs@cpan.org.

📜 MODIFICATION HISTORY

See the Changes file.

©️ COPYRIGHT AND LICENSE

Copyright (c) 2005-2021 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 v5.34.0 2026-06-23 IO::Uncompress::Gunzip(3perl)

📘 NAME 🚀 Quick Reference 📋 SYNOPSIS 📝 DESCRIPTION 📦 Importing 💡 EXAMPLES 📬 SUPPORT 📚 SEE ALSO ✍️ AUTHOR 📜 MODIFICATION HISTORY ©️ COPYRIGHT AND LICENSE