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# IO::Zlib

Perl 5 version 26.0 documentation
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# IO::Zlib

- NAME
- SYNOPSIS
- DESCRIPTION
- CONSTRUCTOR
- OBJECT METHODS
- USING THE EXTERNAL GZIP
- CLASS METHODS
- DIAGNOSTICS
- SEE ALSO
- HISTORY
- COPYRIGHT

# 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.

Page index

- NAME
- SYNOPSIS
- DESCRIPTION
- CONSTRUCTOR
- OBJECT METHODS
- USING THE EXTERNAL GZIP
- CLASS METHODS
- DIAGNOSTICS
- SEE ALSO
- HISTORY
- COPYRIGHT