IO::Uncompress::Gunzip(3) User Contributed Perl Documentation
NAME
IO::Uncompress::Gunzip - Read RFC 1952 files/buffers
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 $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.
o 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.
o 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.
o 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
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";
The constructor takes one mandatory parameter, $input, defined below, and
zero or more "OPTS", defined in "Constructor Options".
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>;
Below is a simple exaple of using the OO interface to read the compressed
file "myfile.gz" and write its contents 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();
See "EXAMPLES" for further examples
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.
This parameter 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.
This parameter 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.
This option defaults to 1.
"BlockSize => $num"
When reading the compressed input data, IO::Uncompress::Gunzip will
read it in blocks of $num bytes.
This option 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.
This option 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.
"NewStreamHook => \&hook" The "hook" sub will only be invoked when the
"MultiStream" option is enabled and the code has detected a new gzip
header.
Ther equivalent data that is returned by "getHeaderInfo"will be
passed into "hook"
A single parameter is passed into the "hook" sub that consists of
the data returned by running the "getHeaderInfo" method on th enew
gzip stream.
"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.
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
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(3), IO::Compress::Gzip(3), IO::Compress::Deflate(3),
IO::Uncompress::Inflate(3), IO::Compress::RawDeflate(3),
IO::Uncompress::RawInflate(3), IO::Compress::Bzip2(3),
IO::Uncompress::Bunzip2(3), IO::Compress::Lzma(3),
IO::Uncompress::UnLzma(3), IO::Compress::Xz(3),
IO::Uncompress::UnXz(3), IO::Compress::Lzip(3),
IO::Uncompress::UnLzip(3), IO::Compress::Lzop(3),
IO::Uncompress::UnLzop(3), IO::Compress::Lzf(3),
IO::Uncompress::UnLzf(3), IO::Compress::Zstd(3),
IO::Uncompress::UnZstd(3), IO::Uncompress::AnyInflate(3),
IO::Uncompress::AnyUncompress(3)
IO::Compress::FAQ(3)
File::GlobMapper(3), Archive::Zip(3), Archive::Tar(3), IO::Zlib(3)
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@outlook.com".
MODIFICATION HISTORY
See the Changes file.
COPYRIGHT AND LICENSE
Copyright (c) 2005-2026 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 v5.34.3 2026-10-10 IO::Uncompress::Gunzip(3)
io-compress 2.225.0 - Generated Sat Oct 10 08:46:55 CDT 2026