Template::Extract(3)

NAME
Template::Extract - Use TT2 syntax to extract data from documents

VERSION
This document describes version 0.41 of Template::Extract, released October 16, 2007.

SYNOPSIS
    use Template::Extract;
    use Data::Dumper;

    my $obj = Template::Extract->new;
    my $template = << '.';
    <ul>[% FOREACH record %]
    <li><A HREF="[% url %]">[% title %]</A>: [% rate %] - [% comment %].
    [% ... %]
    [% END %]</ul>
    .

    my $document = << '.';
    <html><head><title>Great links</title></head><body>
    <ul><li><A HREF="http://slashdot.org">News for nerds.</A>: A+ - nice.
    this text is ignored.</li>
    <li><A HREF="http://microsoft.com">Where do you want...</A>: Z! - yeah.
    this text is ignored, too.</li></ul>
    .

    print Data::Dumper::Dumper(
        $obj->extract($template, $document)
    );

DESCRIPTION
This module adds template extraction functionality to the Template toolkit. It can take a rendered document and its template together, and get the original data structure back, effectively reversing the "Template::process" function.

METHODS

  new(\%options)
Constructor. Currently all options are passed into the underlying "Template::Parser" object. The same set of options are also passed to classes responsible to compile and run the extraction process, but they are currently ignored.

  extract($template, $document, \%values)
This method takes three arguments: the template string, or a reference to it; a document string to match against; and an optional hash reference to supply initial values, as well as storing the extracted values into.

The return value is "\%values" upon success, and "undef" on failure. If "\%values" is omitted from the argument list, a new hash reference will be constructed and returned.

Extraction is done by transforming the result from Template::Parser to a highly esoteric regular expression, which utilizes the "(?{...})" construct to insert matched parameters into the hash reference.

The special "[% ... %]" directive is taken as the "/.*?/s" regex, i.e. ignore everything (as short as possible) between this identifier and the next one. For backward compatibility, "[% _ %]" and "[% __ %]" are also accepted.

The special "[% // %]" directive is taken as a non-capturing regex, embedded inside "/(?:)/s"; for example, "[% /\d*/ %]" matches any number of digits. Capturing parentheses may not be used with this directive, but you can use the "[% var =~ // %]" directive to capture the match into "var".

You may set $Template::Extract::DEBUG to a true value to display generated regular expressions.

The extraction process defaults to succeed even with a partial match. To match the entire document only, set $Template::Extract::EXACT to a true value.

  compile($template)
Use Template::Extract::Compile to perform the first phase of "extract", by returning the regular expression compiled from $template.

  run($regex, $document, \%values)
Use Template::Extract::Run to perform the second phase of "extract", by applying the regular expression on $document and returning the resulting "\%values".

SUBCLASSING
If you would like to use different modules to parse, compile and run the extraction process, simply subclass "Template::Extract" and override the "COMPILE_CLASS", "PARSER_CLASS" and "RUN_CLASS" methods to return alternate class names.

CAVEATS
Currently, the "extract" method only supports "[% GET %]", "[% SET %]" and "[% FOREACH %]" directives, because "[% WHILE %]", "[% CALL %]" and "[% SWITCH %]" blocks are next to impossible to extract correctly.

"[% SET key = "value" %]" only works for simple scalar values.

Outermost "[% FOREACH %]" blocks must match at least once in the document, but inner ones may occur zero times. This is to prevent the regex optimizer from failing prematurely.

There is no support for different PRE_CHOMP and POST_CHOMP settings internally, so extraction could fail silently on extra linebreaks.

It is somewhat awkward to use global variables to control "EXACT" and "DEBUG" behaviour; patches welcome to promote them into per-instance options.

NOTES
This module's companion class, Template::Generate, is still in early experimental stages; it can take data structures and rendered documents, then automagically generates templates to do the transformation. If you are into related research, please mail any ideas to me.

SEE ALSO
Template::Extract::Compile, Template::Extract::Run, Template::Extract::Parser

Template, Template::Generate

Simon Cozens's introduction to this module, in O'Reilly's Spidering Hacks: <http://www.oreillynet.com/pub/a/javascript/excerpt/spiderhacks_chap01/index.html>

Mark Fowler's introduction to this module, in The 2003 Perl Advent Calendar: <http://perladvent.org/2003/5th/>

AUTHORS
Audrey Tang <cpan@audreyt.org>

COPYRIGHT
Copyright 2001, 2002, 2003, 2004, 2005, 2007 by Audrey Tang <cpan@audreyt.org>.

This software is released under the MIT license cited below.

  The "MIT" License
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.