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gzip(3)                              User Contributed Perl Documentation                             gzip(3)



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 "\x1f\x8b" 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 "\x1f\x8b" 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 v5.16.2                                     2006-10-01                                          gzip(3)