perlio::gzip(3pm) [debian man page]
gzip(3pm) User Contributed Perl Documentation gzip(3pm) NAME
PerlIO::gzip - Perl extension to provide a PerlIO layer to gzip/gunzip SYNOPSIS
use PerlIO::gzip; open FOO, "<:gzip", "file.gz" or die $!; print while <FOO>; # And it will be uncompressed... binmode FOO, ":gzip(none)" # Starts reading deflate stream from here on DESCRIPTION
PerlIO::gzip provides a PerlIO layer that manipulates files in the format used by the "gzip" program. Compression and Decompression are implemented, but not together. If you attempt to open a file for reading and writing the open will fail. EXPORT
PerlIO::gzip exports no subroutines or symbols, just a perl layer "gzip" LAYER ARGUMENTS
The "gzip" layer takes a comma separated list of arguments. 4 exclusive options choose the header checking mode: gzip The default. Expects a standard gzip file header for reading, writes a standard gzip file header. none Expects or writes no file header; assumes the file handle is immediately a deflate stream (eg as would be found inside a "zip" file) auto Potentially dangerous. If the first two bytes match the "gzip" header "x1fx8b" then a gzip header is assumed (and checked) else a deflate stream is assumed. No different from gzip on writing. autopop Potentially dangerous. If the first two bytes match the "gzip" header "x1fx8b" then a gzip header is assumed (and checked) else the layer is silently popped. This results in gzip files being transparently decompressed, other files being treated normally. Of course, this has sides effects such as File::Copy becoming gunzip, and File::Compare comparing the uncompressed contents of files. In autopop mode Opening a handle for writing (or reading and writing) will cause the gzip layer to automatically be popped. Optionally you can add this flag: lazy For reading, defer header checking until the first read. For writing, don't write a header until the first buffer empty of compressed data to disk. (and don't write anything at all if no data was written to the handle) By default, gzip header checking is done before the "open" (or "binmode") returns, so if an error is detected in the gzip header the "open" or "binmode" will fail. However, this will require reading some data, or writing a header. With lazy set on a file opened for reading the check is deferred until the first read so the "open" should always succeed, but any problems with the header will cause an error on read. open FOO, "<:gzip(lazy)", "file.gz" or die $!; # Dangerous. while (<FOO>) { print; } # Whoa. Bad. You're not distinguishing between errors and EOF. If you're not careful you won't spot the errors - like the example above you'll think you got end of file. lazy is ignored if you are in autopop mode. AUTHOR
Nicholas Clark, <nwc10+perlio-gzip@colon.colondot.net> SEE ALSO
perl, gzip, rfc 1952 <http://www.ietf.org/rfc/rfc1952.txt> (the gzip file format specification), rfc 1951 <http://www.ietf.org/rfc/rfc1951.txt> (DEFLATE compressed data format specification) perl v5.14.2 2006-10-01 gzip(3pm)
Check Out this Related Man Page
IO::Zlib(3pm) Perl Programmers Reference Guide IO::Zlib(3pm) 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 "; $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 line2 "; 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 " ". 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. perl v5.12.1 2010-04-26 IO::Zlib(3pm)