Manpages - IO_Compress_Gzip.3perl

OPTS] gzip 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 > gzip 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.

In addition, if $input_filename_or_reference 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_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 > gzip 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 gzip 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 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”

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::Gzip=gzip -e gzip \*STDIN => \*STDOUT >output.gz

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::Gzip=gzip -e gzip “-” => “-” >output.gz

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.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”;

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::Gzip qw(gzip $GzipError) ; use IO::File ; my $input = IO::File->new( “<file1.txt” ) or die “Cannot open file1.txt: $!\n” ; my $buffer ; gzip $input => \$buffer or die “gzip failed: $GzipError\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::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”; }

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

my $z = IO::Compress::Gzip->new( $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.

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::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 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.

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::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.

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