Kevin Ryde > Filter-gunzip-4 > Filter::gunzip



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Module Version: 4   Source   Latest Release: Filter-gunzip-6


Filter::gunzip - gunzip Perl source code for execution


 perl -MFilter::gunzip

 use Filter::gunzip;
 ... # inline gzipped source code bytes


This filter uncompresses gzipped Perl code at run-time. It's slightly a proof of concept, but works well as far as it goes. It can be used from the command line to run a .pl.gz file,

    perl -MFilter::gunzip

Or in a self-uncompressing executable beginning with a use and gzip bytes immediately following that line,

    use Filter::gunzip;
    ... raw gzip bytes

The filter is implemented one of two ways. For the usual case that Filter::gunzip is the first filter and PerlIO is available then push a PerlIO::gzip layer. Otherwise add a block-oriented source filter per perlfilter. In both cases the uncompressed code can apply further source filters in the usual way.

DATA Handle

The __DATA__ token ("Special Literals" in perldata) and DATA handle can be used in the compressed source, but only some of the time.

For the PerlIO case the DATA handle is simply the input, including the :gzip uncompressing layer, positioned just after the __DATA__ token. This works well for data compressed along with the code, though PerlIO::gzip as of version 0.18 cannot dup or seek which means for instance SelfLoader doesn't work. (Duping and seeking are probably both feasible, though seeking backward might be slow.)

For the filter case DATA doesn't really work properly. Perl stops reading from the source filters at the __DATA__ token, because that's where the source ends. But a block oriented filter like Filter::gunzip may read ahead in the input file, so the position the DATA handle is left is unpredictable, especially if there's a couple of block-oriented filters stacked up.

Further Details

Perl source is normally read without CRLF translation (in Perl 5.6.1 and up at least). If Filter::gunzip sees a :crlf layer on the input it pushes the :gzip underneath that, since the CRLF is almost certainly meant to apply to the text, not to the raw gzip bytes. This should let it work with the forced PERLIO=crlf suggested by README.cygwin (see "PERLIO" in perlrun).

The gzip format has a CRC checksum at the end of the data. This might catch subtle corruption in the compressed bytes, except as of Perl 5.10 the parser usually doesn't report a read error and in any case the code is compiled and BEGIN blocks are executed as uncompressing proceeds, so corruption will likely provoke a syntax error before the CRC is reached.

Only the gzip format (RFC 1952) is supported. Zlib format (RFC 1950) differs only in the header, but PerlIO::gzip (version 0.18) doesn't allow it. The actual gunzip program can handle some other formats, like Unix .Z compress, but they're probably best left to other modules.

The bzip2 format could be handled by a very similar filter, if .pl.bz2 files were used. Its decompressor uses at least 2.5 Mbytes of memory though, so if choosing that format there'd have to be a big disk saving before it was worth that much memory at runtime.


Filter::exec and the zcat program can the same thing, either from the command line or self-expanding,

    perl -MFilter::exec=zcat

Because Filter::exec is a block-oriented filter (as of version 1.37) a compressed __DATA__ section within the script doesn't work.

PerlIO::gzip can be applied to a script with the open pragma and a require. For example something like the following from the command line. Since the open pragma is lexical it doesn't affect other later loads or opens.

    perl -e '{use open IN=>":gzip";require shift}' \
   arg1 arg2

It doesn't work to set a PERLIO environment variable for a global :gzip layer, eg. PERLIO=':gzip(autopop)', because the default layers are restricted to Perl builtins (see "PERLIO" in perlrun).


PerlIO::gzip, PerlIO, Filter::Util::Call, Filter::exec, gzip(1), zcat(1), open setting up a Filter::gunzip command (and other forms) to run a .pl.gz from Emacs.



Filter-gunzip is Copyright 2010, 2011 Kevin Ryde

Filter-gunzip is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

Filter-gunzip is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with Filter-gunzip. If not, see <>.

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