NAME¶
IO::Compress::Gzip - Write RFC 1952 files/buffers
SYNOPSIS¶
use IO::Compress::Gzip qw(gzip $GzipError) ;
my $status = gzip $input => $output [,OPTS]
or die "gzip failed: $GzipError\n";
my $z = new IO::Compress::Gzip $output [,OPTS]
or die "gzip failed: $GzipError\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() ;
$GzipError ;
# IO::File mode
print $z $string;
printf $z $format, $string;
tell $z
eof $z
seek $z, $position, $whence
binmode $z
fileno $z
close $z ;
DESCRIPTION¶
This module provides a Perl interface that allows writing compressed data to
files or buffer as defined in RFC 1952.
All the gzip headers defined in RFC 1952 can be created using this module.
For reading RFC 1952 files/buffers, see the companion module
IO::Uncompress::Gunzip.
Functional Interface¶
A top-level function, "gzip", is provided to carry out
"one-shot" compression between buffers and/or files. For finer
control over the compression process, see the "OO Interface"
section.
use IO::Compress::Gzip qw(gzip $GzipError) ;
gzip $input => $output [,OPTS]
or die "gzip failed: $GzipError\n";
The functional interface needs Perl5.005 or better.
"gzip" expects at least two parameters, $input and $output.
The $input parameter
The parameter, $input, is used to define the source of the uncompressed data.
It can take one of the following forms:
- A filename
- If the $input 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 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 is a scalar reference, the input data will be
read from $$input.
- An array reference
- If $input is an array reference, each element in the array
must be a filename.
The input data will be read from each file in turn.
The complete array will be walked to ensure that it only contains valid
filenames before any data is compressed.
- An Input FileGlob string
- If $input is a string that is delimited by the characters
"<" and ">" "gzip" will assume that it
is an input fileglob string. The input is the list of files that
match the fileglob.
See File::GlobMapper for more details.
If the $input parameter is any other type, "undef" will be returned.
In addition, if $input is a simple filename, the default values for the
"Name" and "Time" options will be sourced from that file.
If you do not want to use these defaults they can be overridden by explicitly
setting the "Name" and "Time" options or by setting the
"Minimal" parameter.
The $output parameter
The parameter $output is used to control the destination of the compressed data.
This parameter can take one of these forms.
- A filename
- If the $output parameter is a simple scalar, it is assumed
to be a filename. This file will be opened for writing and the compressed
data will be written to it.
- A filehandle
- If the $output parameter is a filehandle, the compressed
data will be written to it. The string '-' can be used as an alias for
standard output.
- A scalar reference
- If $output is a scalar reference, the compressed data will
be stored in $$output.
- An Array Reference
- If $output is an array reference, the compressed data will
be pushed onto the array.
- An Output FileGlob
- If $output is a string that is delimited by the characters
"<" and ">" "gzip" will assume that it
is an output fileglob string. The output is the list of files that
match the fileglob.
When $output is an fileglob string, $input must also be a fileglob string.
Anything else is an error.
See File::GlobMapper for more details.
If the $output parameter is any other type, "undef" will be returned.
Notes¶
When $input maps to multiple files/buffers and $output is a single file/buffer
the input files/buffers will be stored in $output as a concatenated series of
compressed data streams.
Optional Parameters¶
Unless specified below, the optional parameters for "gzip",
"OPTS", are the same as those used with the OO interface defined in
the "Constructor Options" section below.
- "AutoClose => 0|1"
- This option applies to any input or output data streams to
"gzip" 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 "gzip"
has completed.
This parameter defaults to 0.
- "BinModeIn => 0|1"
- When reading from a file or filehandle, set
"binmode" before reading.
Defaults to 0.
- "Append => 0|1"
- The behaviour of this option is dependent on the type of
output data stream.
- •
- A Buffer
If "Append" is enabled, all compressed data will be append to the
end of the output buffer. Otherwise the output buffer will be cleared
before any compressed data is written to it.
- •
- A Filename
If "Append" is enabled, the file will be opened in append mode.
Otherwise the contents of the file, if any, will be truncated before any
compressed data is written to it.
- •
- A Filehandle
If "Append" is enabled, the filehandle will be positioned to the
end of the file via a call to "seek" before any compressed data
is written to it. Otherwise the file pointer will not be moved.
When "Append" is specified, and set to true, it will
append all
compressed data to the output data stream.
So when the output is a filehandle it will carry out a seek to the eof before
writing any compressed data. If the output is a filename, it will be opened
for appending. If the output is a buffer, all compressed data will be appended
to the existing buffer.
Conversely when "Append" is not specified, or it is present and is set
to false, it will operate as follows.
When the output is a filename, it will truncate the contents of the file before
writing any compressed data. If the output is a filehandle its position will
not be changed. If the output is a buffer, it will be wiped before any
compressed data is output.
Defaults to 0.
Examples¶
To read the contents of the file "file1.txt" and write the compressed
data to the file "file1.txt.gz".
use strict ;
use warnings ;
use IO::Compress::Gzip qw(gzip $GzipError) ;
my $input = "file1.txt";
gzip $input => "$input.gz"
or die "gzip failed: $GzipError\n";
To read from an existing Perl filehandle, $input, and write the compressed data
to a buffer, $buffer.
use strict ;
use warnings ;
use IO::Compress::Gzip qw(gzip $GzipError) ;
use IO::File ;
my $input = new IO::File "<file1.txt"
or die "Cannot open 'file1.txt': $!\n" ;
my $buffer ;
gzip $input => \$buffer
or die "gzip failed: $GzipError\n";
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::Gzip qw(gzip $GzipError) ;
gzip '</my/home/*.txt>' => '<*.gz>'
or die "gzip failed: $GzipError\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::Gzip qw(gzip $GzipError) ;
for my $input ( glob "/my/home/*.txt" )
{
my $output = "$input.gz" ;
gzip $input => $output
or die "Error compressing '$input': $GzipError\n";
}
OO Interface¶
Constructor¶
The format of the constructor for "IO::Compress::Gzip" is shown below
my $z = new IO::Compress::Gzip $output [,OPTS]
or die "IO::Compress::Gzip failed: $GzipError\n";
It returns an "IO::Compress::Gzip" object on success and undef on
failure. The variable $GzipError will contain an error message on failure.
If you are running Perl 5.005 or better the object, $z, returned from
IO::Compress::Gzip 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";
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::Gzip"::new
will return undef.
Constructor Options¶
"OPTS" is any combination 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 the
$output being closed once either the "close" method is called or
the "IO::Compress::Gzip" 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
1952 data stream.
There are a number of other limitations with the "Merge"
option:
- 1.
- This module needs to have been built with zlib 1.2.1 or
better to work. A fatal error will be thrown if "Merge" is used
with an older version of zlib.
- 2.
- If $output is a file or a filehandle, it must be
seekable.
This parameter defaults to 0.
- -Level
- Defines the compression level used by zlib. The value
should either be a number between 0 and 9 (0 means no compression and 9 is
maximum compression), or one of the symbolic constants defined below.
Z_NO_COMPRESSION
Z_BEST_SPEED
Z_BEST_COMPRESSION
Z_DEFAULT_COMPRESSION
The default is Z_DEFAULT_COMPRESSION.
Note, these constants are not imported by "IO::Compress::Gzip" by
default.
use IO::Compress::Gzip qw(:strategy);
use IO::Compress::Gzip qw(:constants);
use IO::Compress::Gzip 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.
- "Minimal => 0|1"
- If specified, this option will force the creation of the
smallest possible compliant gzip header (which is exactly 10 bytes long)
as defined in RFC 1952.
See the section titled "Compliance" in RFC 1952 for a definition
of the values used for the fields in the gzip header.
All other parameters that control the content of the gzip header will be
ignored if this parameter is set to 1.
This parameter defaults to 0.
- "Comment => $comment"
- Stores the contents of $comment in the COMMENT field in the
gzip header. By default, no comment field is written to the gzip file.
If the "-Strict" option is enabled, the comment can only consist
of ISO 8859-1 characters plus line feed.
If the "-Strict" option is disabled, the comment field can contain
any character except NULL. If any null characters are present, the field
will be truncated at the first NULL.
- "Name => $string"
- Stores the contents of $string in the gzip NAME header
field. If "Name" is not specified, no gzip NAME field will be
created.
If the "-Strict" option is enabled, $string can only consist of
ISO 8859-1 characters.
If "-Strict" is disabled, then $string can contain any character
except NULL. If any null characters are present, the field will be
truncated at the first NULL.
- "Time => $number"
- Sets the MTIME field in the gzip header to $number.
This field defaults to the time the "IO::Compress::Gzip" object
was created if this option is not specified.
- "TextFlag => 0|1"
- This parameter controls the setting of the FLG.FTEXT bit in
the gzip header. It is used to signal that the data stored in the gzip
file/buffer is probably text.
The default is 0.
- "HeaderCRC => 0|1"
- When true this parameter will set the FLG.FHCRC bit to 1 in
the gzip header and set the CRC16 header field to the CRC of the complete
gzip header except the CRC16 field itself.
Note that gzip files created with the "HeaderCRC" flag set
to 1 cannot be read by most, if not all, of the the standard gunzip
utilities, most notably gzip version 1.2.4. You should therefore avoid
using this option if you want to maximize the portability of your gzip
files.
This parameter defaults to 0.
- "OS_Code => $value"
- Stores $value in the gzip OS header field. A number between
0 and 255 is valid.
If not specified, this parameter defaults to the OS code of the Operating
System this module was built on. The value 3 is used as a catch-all for
all Unix variants and unknown Operating Systems.
- "ExtraField => $data"
- This parameter allows additional metadata to be stored in
the ExtraField in the gzip header. An RFC 1952 compliant ExtraField
consists of zero or more subfields. Each subfield consists of a two byte
header followed by the subfield data.
The list of subfields can be supplied in any of the following formats
-ExtraField => [$id1, $data1,
$id2, $data2,
...
]
-ExtraField => [ [$id1 => $data1],
[$id2 => $data2],
...
]
-ExtraField => { $id1 => $data1,
$id2 => $data2,
...
}
Where $id1, $id2 are two byte subfield ID's. The second byte of the ID
cannot be 0, unless the "Strict" option has been disabled.
If you use the hash syntax, you have no control over the order in which the
ExtraSubFields are stored, plus you cannot have SubFields with duplicate
ID.
Alternatively the list of subfields can by supplied as a scalar, thus
-ExtraField => $rawdata
If you use the raw format, and the "Strict" option is enabled,
"IO::Compress::Gzip" will check that $rawdata consists of zero
or more conformant sub-fields. When "Strict" is disabled,
$rawdata can consist of any arbitrary byte stream.
The maximum size of the Extra Field 65535 bytes.
- "ExtraFlags => $value"
- Sets the XFL byte in the gzip header to $value.
If this option is not present, the value stored in XFL field will be
determined by the setting of the "Level" option.
If "Level => Z_BEST_SPEED" has been specified then XFL is set
to 2. If "Level => Z_BEST_COMPRESSION" has been specified
then XFL is set to 4. Otherwise XFL is set to 0.
- "Strict => 0|1"
- "Strict" will optionally police the values
supplied with other options to ensure they are compliant with RFC1952.
This option is enabled by default.
If "Strict" is enabled the following behaviour will be
policed:
- •
- The value supplied with the "Name" option can
only contain ISO 8859-1 characters.
- •
- The value supplied with the "Comment" option can
only contain ISO 8859-1 characters plus line-feed.
- •
- The values supplied with the "-Name" and
"-Comment" options cannot contain multiple embedded nulls.
- •
- If an "ExtraField" option is specified and it is
a simple scalar, it must conform to the sub-field structure as defined in
RFC 1952.
- •
- If an "ExtraField" option is specified the second
byte of the ID will be checked in each subfield to ensure that it does not
contain the reserved value 0x00.
When "Strict" is disabled the following behaviour will be policed:
- •
- The value supplied with "-Name" option can
contain any character except NULL.
- •
- The value supplied with "-Comment" option can
contain any character except NULL.
- •
- The values supplied with the "-Name" and
"-Comment" options can contain multiple embedded nulls. The
string written to the gzip header will consist of the characters up to,
but not including, the first embedded NULL.
- •
- If an "ExtraField" option is specified and it is
a simple scalar, the structure will not be checked. The only error is if
the length is too big.
- •
- The ID header in an "ExtraField" sub-field can
consist of any two bytes.
Examples¶
TODO
Methods¶
print¶
Usage is
$z->print($data)
print $z $data
Compresses and outputs the contents of the $data parameter. This has the same
behaviour as the "print" built-in.
Returns true if successful.
printf¶
Usage is
$z->printf($format, $data)
printf $z $format, $data
Compresses and outputs the contents of the $data parameter.
Returns true if successful.
syswrite¶
Usage is
$z->syswrite $data
$z->syswrite $data, $length
$z->syswrite $data, $length, $offset
Compresses and outputs the contents of the $data parameter.
Returns the number of uncompressed bytes written, or "undef" if
unsuccessful.
write¶
Usage is
$z->write $data
$z->write $data, $length
$z->write $data, $length, $offset
Compresses and outputs the contents of the $data parameter.
Returns the number of uncompressed bytes written, or "undef" if
unsuccessful.
flush¶
Usage is
$z->flush;
$z->flush($flush_type);
Flushes any pending compressed data to the output file/buffer.
This method takes an optional parameter, $flush_type, that controls how the
flushing will be carried out. By default the $flush_type used is
"Z_FINISH". Other valid values for $flush_type are
"Z_NO_FLUSH", "Z_SYNC_FLUSH", "Z_FULL_FLUSH" and
"Z_BLOCK". It is strongly recommended that you only set the
"flush_type" parameter if you fully understand the implications of
what it does - overuse of "flush" can seriously degrade the level of
compression achieved. See the "zlib" documentation for details.
Returns true on success.
tell¶
Usage is
$z->tell()
tell $z
Returns the uncompressed file offset.
eof¶
Usage is
$z->eof();
eof($z);
Returns true if the "close" method has been called.
seek¶
$z->seek($position, $whence);
seek($z, $position, $whence);
Provides a sub-set of the "seek" functionality, with the restriction
that it is only legal to seek forward in the output file/buffer. It is a fatal
error to attempt to seek backward.
Empty parts of the file/buffer will have NULL (0x00) bytes written to them.
The $whence parameter takes one the usual values, namely SEEK_SET, SEEK_CUR or
SEEK_END.
Returns 1 on success, 0 on failure.
binmode¶
Usage is
$z->binmode
binmode $z ;
This is a noop provided for completeness.
opened¶
$z->opened()
Returns true if the object currently refers to a opened file/buffer.
autoflush¶
my $prev = $z->autoflush()
my $prev = $z->autoflush(EXPR)
If the $z object is associated with a file or a filehandle, this method returns
the current autoflush setting for the underlying filehandle. If
"EXPR" is present, and is non-zero, it will enable flushing after
every write/print operation.
If $z is associated with a buffer, this method has no effect and always returns
"undef".
Note that the special variable $|
cannot be used to set or
retrieve the autoflush setting.
$z->input_line_number()
$z->input_line_number(EXPR)
This method always returns "undef" when compressing.
fileno¶
$z->fileno()
fileno($z)
If the $z object is associated with a file or a filehandle, "fileno"
will return the underlying file descriptor. Once the "close" method
is called "fileno" will return "undef".
If the $z object is associated with a buffer, this method will return
"undef".
close¶
$z->close() ;
close $z ;
Flushes any pending compressed data and then closes the output file/buffer.
For most versions of Perl this method will be automatically invoked if the
IO::Compress::Gzip object is destroyed (either explicitly or by the variable
with the reference to the object going out of scope). The exceptions are Perl
versions 5.005 through 5.00504 and 5.8.0. In these cases, the
"close" method will be called automatically, but not until global
destruction of all live objects when the program is terminating.
Therefore, if you want your scripts to be able to run on all versions of Perl,
you should call "close" explicitly and not rely on automatic
closing.
Returns true on success, otherwise 0.
If the "AutoClose" option has been enabled when the IO::Compress::Gzip
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 the options that are available when creating the $z
object.
See the "Constructor Options" section for more details.
deflateParams¶
Usage is
$z->deflateParams
TODO
Importing¶
A number of symbolic constants are required by some methods in
"IO::Compress::Gzip". None are imported by default.
- :all
- Imports "gzip", $GzipError and all symbolic
constants that can be used by "IO::Compress::Gzip". Same as
doing this
use IO::Compress::Gzip qw(gzip $GzipError :constants) ;
- :constants
- Import all symbolic constants. Same as doing this
use IO::Compress::Gzip 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
SEE ALSO¶
Compress::Zlib, IO::Uncompress::Gunzip, 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::Lzop, IO::Uncompress::UnLzop, IO::Compress::Lzf,
IO::Uncompress::UnLzf, 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.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 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) 2005-2012 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.