IO::Compress::Bzip2(3perl) Perl Programmers Reference Guide IO::Compress::Bzip2(3perl)

IO::Compress::Bzip2 - Write bzip2 files/buffers

use IO::Compress::Bzip2 qw(bzip2 $Bzip2Error) ;
my $status = bzip2 $input => $output [,OPTS]
    or die "bzip2 failed: $Bzip2Error\n";
my $z = IO::Compress::Bzip2->new( $output [,OPTS] )
    or die "bzip2 failed: $Bzip2Error\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->close() ;
$Bzip2Error ;
# IO::File mode
print $z $string;
printf $z $format, $string;
tell $z
eof $z
seek $z, $position, $whence
binmode $z
fileno $z
close $z ;

This module provides a Perl interface that allows writing bzip2 compressed data to files or buffer.

For reading bzip2 files/buffers, see the companion module IO::Uncompress::Bunzip2.

A top-level function, "bzip2", 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::Bzip2 qw(bzip2 $Bzip2Error) ;
bzip2 $input_filename_or_reference => $output_filename_or_reference [,OPTS]
    or die "bzip2 failed: $Bzip2Error\n";

The functional interface needs Perl5.005 or better.

"bzip2" 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 uncompressed data.

It can take one of the following forms:

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.
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.
If $input_filename_or_reference is a scalar reference, the input data will be read from $$input_filename_or_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 compressed.

If $input_filename_or_reference is a string that is delimited by the characters "<" and ">" "bzip2" 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 compressed data. This parameter can take one of these forms.

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 compressed data will be written to it.
If the $output_filename_or_reference parameter is a filehandle, the compressed data will be written to it. The string '-' can be used as an alias for standard output.
If $output_filename_or_reference is a scalar reference, the compressed data will be stored in $$output_filename_or_reference.
If $output_filename_or_reference is an array reference, the compressed data will be pushed onto the array.
If $output_filename_or_reference is a string that is delimited by the characters "<" and ">" "bzip2" 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.

When $input_filename_or_reference maps to multiple files/buffers and $output_filename_or_reference is a single file/buffer the input files/buffers will be stored in $output_filename_or_reference as a concatenated series of compressed data streams.

The optional parameters for the one-shot function "bzip2" 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 "bzip2" 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 "bzip2" has completed.

This parameter defaults to 0.

"BinModeIn => 0|1"
This option is now a no-op. All files will be read in binmode.
"Append => 0|1"
The behaviour of this option is dependent on the type of output data stream.
  • A Buffer

    If "Append" is enabled, all compressed data will be 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.

Here are a few example that show the capabilities of the module.

Streaming

This very simple command line example demonstrates the streaming capabilities of the module. The code reads data from STDIN, compresses it, and writes the compressed data to STDOUT.

$ echo hello world | perl -MIO::Compress::Bzip2=bzip2 -e 'bzip2 \*STDIN => \*STDOUT' >output.bz2

The special filename "-" can be used as a standin for both "\*STDIN" and "\*STDOUT", so the above can be rewritten as

$ echo hello world | perl -MIO::Compress::Bzip2=bzip2 -e 'bzip2 "-" => "-"' >output.bz2

Compressing a file from the filesystem

To read the contents of the file "file1.txt" and write the compressed data to the file "file1.txt.bz2".

use strict ;
use warnings ;
use IO::Compress::Bzip2 qw(bzip2 $Bzip2Error) ;
my $input = "file1.txt";
bzip2 $input => "$input.bz2"
    or die "bzip2 failed: $Bzip2Error\n";

Reading from a Filehandle and writing to an in-memory buffer

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

use strict ;
use warnings ;
use IO::Compress::Bzip2 qw(bzip2 $Bzip2Error) ;
use IO::File ;
my $input = IO::File->new( "<file1.txt" )
    or die "Cannot open 'file1.txt': $!\n" ;
my $buffer ;
bzip2 $input => \$buffer
    or die "bzip2 failed: $Bzip2Error\n";

Compressing multiple files

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

use strict ;
use warnings ;
use IO::Compress::Bzip2 qw(bzip2 $Bzip2Error) ;
bzip2 '</my/home/*.txt>' => '<*.bz2>'
    or die "bzip2 failed: $Bzip2Error\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::Bzip2 qw(bzip2 $Bzip2Error) ;
for my $input ( glob "/my/home/*.txt" )
{
    my $output = "$input.bz2" ;
    bzip2 $input => $output
        or die "Error compressing '$input': $Bzip2Error\n";
}

The format of the constructor for "IO::Compress::Bzip2" is shown below

my $z = IO::Compress::Bzip2->new( $output [,OPTS] )
    or die "IO::Compress::Bzip2 failed: $Bzip2Error\n";

The constructor takes one mandatory parameter, $output, defined below and zero or more "OPTS", defined in "Constructor Options".

It returns an "IO::Compress::Bzip2" object on success and "undef" on failure. The variable $Bzip2Error will contain an error message on failure.

If you are running Perl 5.005 or better the object, $z, returned from IO::Compress::Bzip2 can be used exactly like an IO::File filehandle. This means that all normal output file operations can be carried out with $z. For example, to write to a compressed file/buffer you can use either of these forms

$z->print("hello world\n");
print $z "hello world\n";

Below is a simple exaple of using the OO interface to create an output file "myfile.bz2" and write some data to it.

my $filename = "myfile.bz2";
my $z = IO::Compress::Bzip2->new($filename)
    or die "IO::Compress::Bzip2 failed: $Bzip2Error\n";
$z->print("abcde");
$z->close();

See the "Examples" for more.

The mandatory parameter $output is used to control the destination of the compressed data. This parameter can take one of these forms.

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.
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.
If $output is a scalar reference, the compressed data will be stored in $$output.

If the $output parameter is any other type, "IO::Compress::Bzip2"::new will return undef.

"OPTS" is any combination of zero or more 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::Bzip2" 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.

"BlockSize100K => number"
Specify the number of 100K blocks bzip2 uses during compression.

Valid values are from 1 to 9, where 9 is best compression.

The default is 1.

"WorkFactor => number"
Specifies how much effort bzip2 should take before resorting to a slower fallback compression algorithm.

Valid values range from 0 to 250, where 0 means use the default value 30.

The default is 0.

"Strict => 0|1"
This is a placeholder option.

Streaming

This very simple command line example demonstrates the streaming capabilities of the module. The code reads data from STDIN or all the files given on the commandline, compresses it, and writes the compressed data to STDOUT.

use strict ;
use warnings ;
use IO::Compress::Bzip2 qw(bzip2 $Bzip2Error) ;
my $z = IO::Compress::Bzip2->new("-", Stream => 1)
    or die "IO::Compress::Bzip2 failed: $Bzip2Error\n";
while (<>) {
    $z->print("abcde");
}
$z->close();

Note the use of "-" to means "STDOUT". Alternatively you can use "\*STDOUT".

Compressing a file from the filesystem

To read the contents of the file "file1.txt" and write the compressed data to the file "file1.txt.bz2" there are a few options

Start by creating the compression object and opening the input file

use strict ;
use warnings ;
use IO::Compress::Bzip2 qw(bzip2 $Bzip2Error) ;
my $input = "file1.txt";
my $z = IO::Compress::Bzip2->new("file1.txt.bz2")
    or die "IO::Compress::Bzip2 failed: $Bzip2Error\n";
# open the input file
open my $fh, "<", "file1.txt"
    or die "Cannot open file1.txt: $!\n";
# loop through the input file & write to the compressed file
while (<$fh>) {
    $z->print($_);
}
# not forgetting to close the compressed file
$z->close();

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.

Usage is

$z->printf($format, $data)
printf $z $format, $data

Compresses and outputs the contents of the $data parameter.

Returns true if successful.

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.

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.

Usage is

$z->flush;

Flushes any pending compressed data to the output file/buffer.

TODO

Returns true on success.

Usage is

$z->tell()
tell $z

Returns the uncompressed file offset.

Usage is

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

Returns true if the "close" method has been called.

$z->seek($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.

Usage is

$z->binmode
binmode $z ;

This is a noop provided for completeness.

$z->opened()

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

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.

$z->fileno()
fileno($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".

$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::Bzip2 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::Bzip2 object was created, and the object is associated with a file, the underlying file will also be closed.

Usage is

$z->newStream( [OPTS] )

Closes the current compressed data stream and starts a new one.

OPTS consists of any of the options that are available when creating the $z object.

See the "Constructor Options" section for more details.

No symbolic constants are required by IO::Compress::Bzip2 at present.

:all
Imports "bzip2" and $Bzip2Error. Same as doing this 
use IO::Compress::Bzip2 qw(bzip2 $Bzip2Error) ;

See IO::Compress::FAQ

See IO::Compress::FAQ

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.

Compress::Zlib, IO::Compress::Gzip, IO::Uncompress::Gunzip, IO::Compress::Deflate, IO::Uncompress::Inflate, IO::Compress::RawDeflate, IO::Uncompress::RawInflate, 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

The primary site for the bzip2 program is https://sourceware.org/bzip2/.

See the module Compress::Bzip2

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

See the Changes file.

Copyright (c) 2005-2024 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.

2024-09-01 perl v5.40.0