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IO::Zlib

Perl 5 version 12.3 documentation
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IO::Zlib

NAME

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

SYNOPSIS

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

  1. use IO::Zlib;
  2. $fh = new IO::Zlib;
  3. if ($fh->open("file.gz", "rb")) {
  4. print <$fh>;
  5. $fh->close;
  6. }
  7. $fh = IO::Zlib->new("file.gz", "wb9");
  8. if (defined $fh) {
  9. print $fh "bar\n";
  10. $fh->close;
  11. }
  12. $fh = IO::Zlib->new("file.gz", "rb");
  13. if (defined $fh) {
  14. print <$fh>;
  15. undef $fh; # automatically closes the file
  16. }

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

  1. use IO::Zlib;
  2. tie *FILE, 'IO::Zlib', "file.gz", "wb";
  3. print FILE "line 1\nline2\n";
  4. tie *FILE, 'IO::Zlib', "file.gz", "rb";
  5. 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

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

If explicitly enabled by

  1. 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 opens are used:

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

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

  1. use IO::Zlib ':gzip_read_open' => '/some/where/gunzip -c %s |';
  2. 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.