Manpages - IO_Compress_Deflate.3perl

[, OPTS] deflate 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:

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 compressed.

An Input FileGlob string

If $input_filename_or_reference is a string that is delimited by the characters < and > deflate will assume that it is an input fileglob string. The input is the list of files that match the fileglob. See :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.

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 compressed data will be written to it.

A filehandle

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.

A scalar reference

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

An Array Reference

If $output_filename_or_reference is an array reference, the compressed 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 > deflate 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 :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 deflate 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 deflate 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 deflate 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::Deflate=deflate -e deflate \*STDIN => \*STDOUT >output.1950

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::Deflate=deflate -e deflate “-” => “-” >output.1950

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.1950.

use strict ; use warnings ; use IO::Compress::Deflate qw(deflate $DeflateError) ; my $input = “file1.txt”; deflate $input => “$input.1950” or die “deflate failed: $DeflateError\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::Deflate qw(deflate $DeflateError) ; use IO::File ; my $input = IO::File->new( “<file1.txt” ) or die “Cannot open file1.txt: $!\n” ; my $buffer ; deflate $input => \$buffer or die “deflate failed: $DeflateError\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::Deflate qw(deflate $DeflateError) ; deflate </my/home/*.txt> => <*.1950> or die “deflate failed: $DeflateError\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::Deflate qw(deflate $DeflateError) ; for my $input ( glob “/my/home/*.txt” ) { my $output = “$input.1950” ; deflate $input => $output or die “Error compressing $input: $DeflateError\n”; }

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

my $z = IO::Compress::Deflate->new( $output [,OPTS] ) or die “IO::Compress::Deflate failed: $DeflateError\n”;

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

If you are running Perl 5.005 or better the object, $z, returned from IO::Compress::Deflate 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::Deflate::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::Deflate 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 1950 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::Deflate by default. use IO::Compress::Deflate qw(:strategy); use IO::Compress::Deflate qw(:constants); use IO::Compress::Deflate 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.

“Strict => 0|1”

This is a placeholder option.

TODO

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; $z->flush($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.

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::Deflate 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::Deflate 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.

Usage is

$z->deflateParams

TODO

See IO::Compress::FAQ

See IO::Compress::FAQ