gzip(3) User Contributed Perl Documentation gzip(3)NAMEPerlIO::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
DESCRIPTIONPerlIO::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.
EXPORTPerlIO::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)
