IO::Zlib(3p) | Perl Programmers Reference Guide | IO::Zlib(3p)

# 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.

# SEE ALSO

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

# HISTORY

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

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

# COPYRIGHT

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.

2025-01-28 | perl v5.40.1