Zlib

Section: User Contributed Perl Documentation (3)
Updated: 2021-01-27
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NAME

IO::Zlib - IO:: style interface to Compress::Zlib

SYNOPSIS

With any version of Perl 5 you can use the basic OO interface:

    use IO::Zlib;

    $fh = new IO::Zlib;
    if ($fh->open("file.gz", "rb")) {
        print <$fh>;
        $fh->close;
    }

    $fh = IO::Zlib->new("file.gz", "wb9");
    if (defined $fh) {
        print $fh "bar\n";
        $fh->close;
    }

    $fh = IO::Zlib->new("file.gz", "rb");
    if (defined $fh) {
        print <$fh>;
        undef $fh;       # automatically closes the file
    }

With Perl 5.004 you can also use the TIEHANDLE interface to access compressed files just like ordinary files:

    use IO::Zlib;

    tie *FILE, 'IO::Zlib', "file.gz", "wb";
    print FILE "line 1\nline2\n";

    tie *FILE, 'IO::Zlib', "file.gz", "rb";
    while (<FILE>) { print "LINE: ", $_ };

DESCRIPTION

"IO::Zlib" provides an IO:: style interface to Compress::Zlib and hence to gzip/zlib compressed files. It provides many of the same methods as the IO::Handle interface.

Starting from IO::Zlib version 1.02, IO::Zlib can also use an external gzip command. The default behaviour is to try to use an external gzip if no "Compress::Zlib" can be loaded, unless explicitly disabled by

    use IO::Zlib qw(:gzip_external 0);

If explicitly enabled by

    use IO::Zlib qw(:gzip_external 1);

then the external gzip is used instead of "Compress::Zlib".

CONSTRUCTOR

new ( [ARGS] ): Creates an "IO::Zlib" object. If it receives any parameters, they are passed to the method "open"; if the open fails, the object is destroyed. Otherwise, it is returned to the caller.

OBJECT METHODS

open ( FILENAME, MODE ): "open" takes two arguments. The first is the name of the file to open and the second is the open mode. The mode can be anything acceptable to Compress::Zlib and by extension anything acceptable to zlib (that basically means POSIX fopen() style mode strings plus an optional number to indicate the compression level).
opened: Returns true if the object currently refers to a opened file.
close: Close the file associated with the object and disassociate the file from the handle. Done automatically on destroy.
getc: Return the next character from the file, or undef if none remain.
getline: Return the next line from the file, or undef on end of string. Can safely be called in an array context. Currently ignores $/ ($INPUT_RECORD_SEPARATOR or $RS when English is in use) and treats lines as delimited by ``\n''.
getlines: Get all remaining lines from the file. It will croak() if accidentally called in a scalar context.
print ( ARGS... ): Print ARGS to the file.
read ( BUF, NBYTES, [OFFSET] ): Read some bytes from the file. Returns the number of bytes actually read, 0 on end-of-file, undef on error.
eof: Returns true if the handle is currently positioned at end of file?
seek ( OFFSET, WHENCE ): Seek to a given position in the stream. Not yet supported.
tell: Return the current position in the stream, as a numeric offset. Not yet supported.
setpos ( POS ): Set the current position, using the opaque value returned by "getpos()". Not yet supported.
getpos ( POS ): Return the current position in the string, as an opaque object. Not yet supported.

USING THE EXTERNAL GZIP

If the external gzip is used, the following "open"s are used:

    open(FH, "gzip -dc $filename |")  # for read opens
    open(FH, " | gzip > $filename")   # for write opens

You can modify the 'commands' for example to hardwire an absolute path by e.g.

    use IO::Zlib ':gzip_read_open'  => '/some/where/gunzip -c %s |';
    use IO::Zlib ':gzip_write_open' => '| /some/where/gzip.exe > %s';

The %s is expanded to be the filename ("sprintf" is used, so be careful to escape any other "%" signs). The 'commands' are checked for sanity - they must contain the %s, and the read open must end with the pipe sign, and the write open must begin with the pipe sign.

CLASS METHODS

has_Compress_Zlib: Returns true if "Compress::Zlib" is available. Note that this does not mean that "Compress::Zlib" is being used: see ``gzip_external'' and gzip_used.
gzip_external: Undef if an external gzip can be used if "Compress::Zlib" is not available (see ``has_Compress_Zlib''), true if an external gzip is explicitly used, false if an external gzip must not be used. See ``gzip_used''.
gzip_used: True if an external gzip is being used, false if not.
gzip_read_open: Return the 'command' being used for opening a file for reading using an external gzip.
gzip_write_open: Return the 'command' being used for opening a file for writing using an external gzip.

DIAGNOSTICS

IO::Zlib::getlines: must be called in list context: If you want read lines, you must read in list context.
IO::Zlib::gzopen_external: mode '...' is illegal: Use only modes 'rb' or 'wb' or /wb[1-9]/.
IO::Zlib::import: '...' is illegal: The known import symbols are the ":gzip_external", ":gzip_read_open", and ":gzip_write_open". Anything else is not recognized.
IO::Zlib::import: ':gzip_external' requires an argument: The ":gzip_external" requires one boolean argument.
IO::Zlib::import: 'gzip_read_open' requires an argument: The ":gzip_external" requires one string argument.
IO::Zlib::import: 'gzip_read' '...' is illegal: The ":gzip_read_open" argument must end with the pipe sign (|) and have the %s for the filename. See ``USING THE EXTERNAL GZIP''.
IO::Zlib::import: 'gzip_write_open' requires an argument: The ":gzip_external" requires one string argument.
IO::Zlib::import: 'gzip_write_open' '...' is illegal: The ":gzip_write_open" argument must begin with the pipe sign (|) and have the %s for the filename. An output redirect (>) is also often a good idea, depending on your operating system shell syntax. See ``USING THE EXTERNAL GZIP''.
IO::Zlib::import: no Compress::Zlib and no external gzip: Given that we failed to load "Compress::Zlib" and that the use of
an external gzip was disabled, IO::Zlib has not much chance of working.
IO::Zlib::open: needs a filename: No filename, no open.
IO::Zlib::READ: NBYTES must be specified: We must know how much to read.
IO::Zlib::WRITE: too long LENGTH: The LENGTH must be less than or equal to the buffer size.

HISTORY

Created by Tom Hughes <tom@compton.nu>.

Support for external gzip added by Jarkko Hietaniemi <jhi@iki.fi>.