NAME

IO::Compress::Zstd - Write zstd files/buffers

SYNOPSIS

use IO::Compress::Zstd qw(zstd $ZstdError) ;

my $status = zstd $input => $output [,OPTS]
    or die "zstd failed: $ZstdError\n";

my $z = IO::Compress::Zstd->new( $output [,OPTS] )
    or die "zstd failed: $ZstdError\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() ;

$ZstdError ;

# 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 zstd compressed data to files or buffer.

For reading zstd files/buffers, see the companion module IO::Uncompress::UnZstd.

Functional Interface

A top-level function, zstd, 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::Zstd qw(zstd $ZstdError) ;

zstd $input_filename_or_reference => $output_filename_or_reference [,OPTS]
    or die "zstd failed: $ZstdError\n";

The functional interface needs Perl5.005 or better.

zstd $input_filename_or_reference => $output_filename_or_reference [, OPTS]

zstd 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 ">" zstd 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.

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 ">" zstd 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 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.

Optional Parameters

The optional parameters for the one-shot function zstd 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 zstd 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 zstd 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.

Oneshot Examples

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::Zstd=zstd -e 'zstd \*STDIN => \*STDOUT' >output.zst

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::Zstd=zstd -e 'zstd "-" => "-"' >output.zst

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.zst.

use strict ;
use warnings ;
use IO::Compress::Zstd qw(zstd $ZstdError) ;

my $input = "file1.txt";
zstd $input => "$input.zst"
    or die "zstd failed: $ZstdError\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::Zstd qw(zstd $ZstdError) ;
use IO::File ;

my $input = IO::File->new( "<file1.txt" )
    or die "Cannot open 'file1.txt': $!\n" ;
my $buffer ;
zstd $input => \$buffer
    or die "zstd failed: $ZstdError\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::Zstd qw(zstd $ZstdError) ;

zstd '</my/home/*.txt>' => '<*.zst>'
    or die "zstd failed: $ZstdError\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::Zstd qw(zstd $ZstdError) ;

for my $input ( glob "/my/home/*.txt" )
{
    my $output = "$input.zst" ;
    zstd $input => $output
        or die "Error compressing '$input': $ZstdError\n";
}

OO Interface

Constructor

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

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

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

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

If you are running Perl 5.005 or better the object, $z, returned from IO::Compress::Zstd 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.zst and write some data to it.

my $filename = "myfile.zst";
my $z = IO::Compress::Zstd->new($filename)
    or die "IO::Compress::Zstd failed: $ZstdError\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.

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::Zstd::new will return undef.

Constructor Options

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::Zstd 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.

Level => number

Defines the compression level used.

This gets passed to the ZSTD function ZSTD_initCStream.

Default is 3

Strict => 0|1

This is a placeholder option.

Examples

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::Zstd qw(zstd $ZstdError) ;

my $z = IO::Compress::Zstd->new("-", Stream => 1)
    or die "IO::Compress::Zstd failed: $ZstdError\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.zst there are a few options

Start by creating the compression object and opening the input file

use strict ;
use warnings ;
use IO::Compress::Zstd qw(zstd $ZstdError) ;

my $input = "file1.txt";
my $z = IO::Compress::Zstd->new("file1.txt.zst")
    or die "IO::Compress::Zstd failed: $ZstdError\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();

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;

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

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.

input_line_number

$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::Zstd 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::Zstd 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 options that are available when creating the $z object.

See the "Constructor Options" section for more details.

Importing

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

:all

Imports zstd and $ZstdError. Same as doing this

use IO::Compress::Zstd qw(zstd $ZstdError) ;

EXAMPLES

SUPPORT

General feedback/questions/bug reports should be sent to https://github.com/pmqs/IO-Compress-Zstd/issues (preferred) or https://rt.cpan.org/Public/Dist/Display.html?Name=IO-Compress-Zstd.

AUTHOR

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

MODIFICATION HISTORY

See the Changes file.

COPYRIGHT AND LICENSE

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

To install IO::Compress::Zstd, copy and paste the appropriate command in to your terminal.

cpanm

cpanm IO::Compress::Zstd

CPAN shell

perl -MCPAN -e shell
install IO::Compress::Zstd

For more information on module installation, please visit the detailed CPAN module installation guide.

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NAME

SYNOPSIS

DESCRIPTION

Functional Interface

zstd $input_filename_or_reference => $output_filename_or_reference [, OPTS]

The $input_filename_or_reference parameter

The $output_filename_or_reference parameter

Notes

Optional Parameters

Oneshot Examples

Streaming

Compressing a file from the filesystem

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

Compressing multiple files

OO Interface

Constructor

Constructor Options

Examples

Streaming

Compressing a file from the filesystem

Methods

print

printf

syswrite

write

flush

tell

eof

seek

binmode

opened

autoflush

input_line_number

fileno

close

newStream([OPTS])

Importing

EXAMPLES

SUPPORT

SEE ALSO

AUTHOR

MODIFICATION HISTORY

COPYRIGHT AND LICENSE

Module Install Instructions

The `$input_filename_or_reference` parameter

The `$output_filename_or_reference` parameter