PerlIO::gzip(3pm)

1gzip(3)               User Contributed Perl Documentation              gzip(3)
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NAME

6       PerlIO::gzip - Perl extension to provide a PerlIO layer to gzip/gunzip
7

SYNOPSIS

9         use PerlIO::gzip;
10         open FOO, "<:gzip", "file.gz" or die $!;
11         print while <FOO>; # And it will be uncompressed...
12
13         binmode FOO, ":gzip(none)" # Starts reading deflate stream from here on
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DESCRIPTION

16       PerlIO::gzip provides a PerlIO layer that manipulates files in the
17       format used by the "gzip" program.  Compression and Decompression are
18       implemented, but not together.  If you attempt to open a file for
19       reading and writing the open will fail.
20

EXPORT

22       PerlIO::gzip exports no subroutines or symbols, just a perl layer
23       "gzip"
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LAYER ARGUMENTS

26       The "gzip" layer takes a comma separated list of arguments. 4 exclusive
27       options choose the header checking mode:
28
29       gzip
30           The default.  Expects a standard gzip file header for reading,
31           writes a standard gzip file header.
32
33       none
34           Expects or writes no file header; assumes the file handle is
35           immediately a deflate stream (eg as would be found inside a "zip"
36           file)
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38       auto
39           Potentially dangerous. If the first two bytes match the "gzip"
40           header "\x1f\x8b" then a gzip header is assumed (and checked) else
41           a deflate stream is assumed.  No different from gzip on writing.
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43       autopop
44           Potentially dangerous. If the first two bytes match the "gzip"
45           header "\x1f\x8b" then a gzip header is assumed (and checked) else
46           the layer is silently popped.  This results in gzip files being
47           transparently decompressed, other files being treated normally.  Of
48           course, this has sides effects such as File::Copy becoming gunzip,
49           and File::Compare comparing the uncompressed contents of files.
50
51           In autopop mode Opening a handle for writing (or reading and
52           writing) will cause the gzip layer to automatically be popped.
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54       Optionally you can add this flag:
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56       lazy
57           For reading, defer header checking until the first read.  For
58           writing, don't write a header until the first buffer empty of
59           compressed data to disk.  (and don't write anything at all if no
60           data was written to the handle)
61
62           By default, gzip header checking is done before the "open" (or
63           "binmode") returns, so if an error is detected in the gzip header
64           the "open" or "binmode" will fail.  However, this will require
65           reading some data, or writing a header.  With lazy set on a file
66           opened for reading the check is deferred until the first read so
67           the "open" should always succeed, but any problems with the header
68           will cause an error on read.
69
70             open FOO, "<:gzip(lazy)", "file.gz" or die $!; # Dangerous.
71             while (<FOO>) {
72               print;
73             } # Whoa. Bad. You're not distinguishing between errors and EOF.
74
75           If you're not careful you won't spot the errors - like the example
76           above you'll think you got end of file.
77
78           lazy is ignored if you are in autopop mode.
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AUTHOR

81       Nicholas Clark, <nwc10+perlio-gzip@colon.colondot.net>
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NAME

SYNOPSIS

DESCRIPTION

EXPORT

LAYER ARGUMENTS

AUTHOR

SEE ALSO