# phpman > perldoc > Dpkg::Compression::FileHandle

## NAME
    [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown) - class dealing transparently with file compression

## SYNOPSIS
        use [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown);

        my ($fh, @lines);

        $fh = [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown)->new(filename => 'sample.gz');
        print $fh "Something\n";
        close $fh;

        $fh = [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown)->new();
        open($fh, '>', 'sample.bz2');
        print $fh "Something\n";
        close $fh;

        $fh = [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown)->new();
        $fh->open('sample.xz', 'w');
        $fh->print("Something\n");
        $fh->close();

        $fh = [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown)->new(filename => 'sample.gz');
        @lines = <$fh>;
        close $fh;

        $fh = [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown)->new();
        open($fh, '<', 'sample.bz2');
        @lines = <$fh>;
        close $fh;

        $fh = [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown)->new();
        $fh->open('sample.xz', 'r');
        @lines = $fh->getlines();
        $fh->close();

## DESCRIPTION
    [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown) is a class that can be used like any filehandle and that deals
    transparently with compressed files. By default, the compression scheme is guessed from the
    filename but you can override this behaviour with the method "set_compression".

    If you don't open the file explicitly, it will be auto-opened on the first read or write
    operation based on the filename set at creation time (or later with the "set_filename" method).

    Once a file has been opened, the filehandle must be closed before being able to open another
    file.

## STANDARD FUNCTIONS
    The standard functions acting on filehandles should accept a [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown)
    object transparently including "open" (only when using the variant with 3 parameters), "close",
    "binmode", "eof", "fileno", "getc", "print", "printf", "read", "sysread", "say", "write",
    "syswrite", "seek", "sysseek", "tell".

    Note however that "seek" and "sysseek" will only work on uncompressed files as compressed files
    are really pipes to the compressor programs and you can't seek on a pipe.

## FileHandle METHODS
    The class inherits from [IO::File](https://www.chedong.com/phpMan.php/perldoc/IO%3A%3AFile/markdown) so all methods that work on this class should work for
    [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown) too. There may be exceptions though.

## PUBLIC METHODS
    $fh = [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown)->new(%opts)
        Creates a new filehandle supporting on-the-fly compression/decompression. Supported options
        are "filename", "compression", "compression_level" (see respective set_* functions) and
        "add_comp_ext". If "add_comp_ext" evaluates to true, then the extension corresponding to the
        selected compression scheme is automatically added to the recorded filename. It's obviously
        incompatible with automatic detection of the compression method.

    $fh->ensure_open($mode, %opts)
        Ensure the file is opened in the requested mode ("r" for read and "w" for write). The
        options are passed down to the compressor's spawn() call, if one is used. Opens the file
        with the recorded filename if needed. If the file is already open but not in the requested
        mode, then it errors out.

    $fh->set_compression($comp)
        Defines the compression method used. $comp should one of the methods supported by
        [Dpkg::Compression](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression/markdown) or "none" or "auto". "none" indicates that the file is uncompressed and
        "auto" indicates that the method must be guessed based on the filename extension used.

    $fh->set_compression_level($level)
        Indicate the desired compression level. It should be a value accepted by the function
        "compression_is_valid_level" of [Dpkg::Compression](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression/markdown).

    $fh->set_filename($name, [$add_comp_ext])
        Use $name as filename when the file must be opened/created. If $add_comp_ext is passed, it
        indicates whether the default extension of the compression method must be automatically
        added to the filename (or not).

    $file = $fh->get_filename()
        Returns the filename that would be used when the filehandle must be opened (both in read and
        write mode). This function errors out if "add_comp_ext" is enabled while the compression
        method is set to "auto". The returned filename includes the extension of the compression
        method if "add_comp_ext" is enabled.

    $ret = $fh->use_compression()
        Returns "0" if no compression is used and the compression method used otherwise. If the
        compression is set to "auto", the value returned depends on the extension of the filename
        obtained with the get_filename method.

    $real_fh = $fh->get_filehandle()
        Returns the real underlying filehandle. Useful if you want to pass it along in a derived
        class.

## DERIVED CLASSES
    If you want to create a class that inherits from [Dpkg::Compression::FileHandle](https://www.chedong.com/phpMan.php/perldoc/Dpkg%3A%3ACompression%3A%3AFileHandle/markdown) you must be aware
    that the object is a reference to a GLOB that is returned by [Symbol::gensym](https://www.chedong.com/phpMan.php/perldoc/Symbol%3A%3Agensym/markdown)() and as such it's
    not a HASH.

    You can store internal data in a hash but you have to use "*$self-"{...}> to access the
    associated hash like in the example below:

        sub set_option {
            my ($self, $value) = @_;
            *$self->{option} = $value;
        }

## CHANGES
  Version 1.01 (dpkg 1.17.11)
    New argument: $fh->ensure_open() accepts an %opts argument.

  Version 1.00 (dpkg 1.15.6)
    Mark the module as public.