gzip $input_filename_or_reference => $output_filename_or_reference [, 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 File::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 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 "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.

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::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";
    }

Constructor¶

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";

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

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";

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

    my $filename = "myfile.gz";
    my $z = IO::Compress::Gzip->new($filename)
        or die "IO::Compress::Gzip failed: $GzipError\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::Gzip"::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::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.

"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:

-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:

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::Gzip qw(gzip $GzipError) ;
    my $z = IO::Compress::Gzip->new("-", Stream => 1)
        or die "IO::Compress::Gzip failed: $GzipError\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.gz" there are a few options

Start by creating the compression object and opening the input file

    use strict ;
    use warnings ;
    use IO::Compress::Gzip qw(gzip $GzipError) ;
    my $input = "file1.txt";
    my $z = IO::Compress::Gzip->new("file1.txt.gz")
        or die "IO::Compress::Gzip failed: $GzipError\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();

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.

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

See the "Constructor Options" section for more details.

deflateParams¶

Usage is

    $z->deflateParams

TODO

Apache::GZip Revisited¶

See IO::Compress::FAQ

Working with Net::FTP¶

See IO::Compress::FAQ