IO::Zlib(3pm) Perl Programmers Reference Guide IO::Zlib(3pm)

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

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: ", $_ };

"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".

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.

"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).
Returns true if the object currently refers to a opened file.
Close the file associated with the object and disassociate the file from the handle. Done automatically on destroy.
Return the next character from the file, or undef if none remain.
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".
Get all remaining lines from the file. It will croak() if accidentally called in a scalar context.
Print ARGS to the file.
Read some bytes from the file. Returns the number of bytes actually read, 0 on end-of-file, undef on error.
Returns true if the handle is currently positioned at end of file?
Seek to a given position in the stream. Not yet supported.
Return the current position in the stream, as a numeric offset. Not yet supported.
Set the current position, using the opaque value returned by "getpos()". Not yet supported.
Return the current position in the string, as an opaque object. Not yet supported.

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.

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.
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".
True if an external gzip is being used, false if not.
Return the 'command' being used for opening a file for reading using an external gzip.
Return the 'command' being used for opening a file for writing using an external gzip.

If you want read lines, you must read in list context.
Use only modes 'rb' or 'wb' or /wb[1-9]/.
The known import symbols are the ":gzip_external", ":gzip_read_open", and ":gzip_write_open". Anything else is not recognized.
The ":gzip_external" requires one boolean argument.
The ":gzip_external" requires one string argument.
The ":gzip_read_open" argument must end with the pipe sign (|) and have the %s for the filename. See "USING THE EXTERNAL GZIP".
The ":gzip_external" requires one string argument.
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".
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.
No filename, no open.
We must know how much to read.
The LENGTH must be less than or equal to the buffer size.

perlfunc, "I/O Operators" in perlop, IO::Handle, Compress::Zlib

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

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

Copyright (c) 1998-2004 Tom Hughes <tom@compton.nu>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

2022-02-19 perl v5.34.1