intro(3)

NAME

Template::Manual::Intro - Introduction to the Template
Toolkit

DESCRIPTION

This section provides a general introduction to the Tem
plate Toolkit, giving a quick overview of features, exam
ples of template directives and use of the Template.pm
module. It also described the basic concept underlying the
toolkit: the separation of presentation elements from
application logic and data.

The Template Toolkit is a collection of modules which
implement a fast, flexible, powerful and extensible tem
plate processing system. It was originally designed and
remains primarily useful for generating dynamic web con
tent, but it can be used equally well for processing any
kind of text documents. This POD documentation is all
generated using the Template Toolkit batch mode utility
ttree, for example.

At the simplest level it provides an easy way to process template files, filling in embedded variable references with their equivalent values.: Dear [% name %],; It has come to our attention that your account is in
arrears to the sum of [% debt %].; Please settle your account before [% deadline %] or we
will be forced to revoke your Licence to Thrill.; The Management.
By default, template directives are embedded within the character sequences '[%' ... '%]' but you can change these and various other options to configure how the Template Toolkit looks, feels and works. You can set the INTERPO LATE option, for example, if you prefer to embed your variables in Perl style:: Dear $name,; It has come to our attention that your account is in
arrears to the sum of $debt.
...
Template.pm
The Template.pm module is the front end to the Template Toolkit, providing access to the full range of functional ity through a single module with a simple interface. It loads the other modules as required and instantiates a default set of objects to handle subsequent template pro cessing requests. Configuration parameters may be passed to the Template.pm constructor, new(), which are then used to configure the underlying objects.: use Template;; my $tt = Template->new({
INCLUDE_PATH => '/usr/local/templates',
INTERPOLATE => 1,; }) || die "$Template::ERROR0;
The Template object implements a process() method for pro cessing template files or text. The name of the input template (or various other sources) is passed as the first argument, followed by a reference to a hash array of vari able definitions for substitution in the template.: my $vars = {
name => 'Count Edward van Halen',
debt => '3 riffs and a solo',
deadline => 'the next chorus',; };; $tt->process('letters/overdrawn', $vars)
|| die $tt->error(), "0;
The process() method returns true (1) on success and prints the template output to STDOUT, by default. On error, the process() method returns false (undef). The error() method can then be called to retrieve details of the error.
Component Based Content Construction
A number of special directives are provided, such as INSERT, INCLUDE and PROCESS, which allow content to be built up from smaller template components. This permits a modular approach to building a web site or other content repository, promoting reusability, cross-site consistency, ease of construction and subsequent maintenance. Common elements such as headers, footers, menu bars, tables, and so on, can be created as separate template files which can then be processed into other documents as required. All defined variables are inherited by these templates along with any additional "local" values specified.: [% PROCESS header
title = "The Cat Sat on the Mat"; %]; [% PROCESS menu %]; The location of the missing feline has now been estab; lished.
Thank you for your assistance.; [% INSERT legal/disclaimer %]; [% PROCESS footer %]
You can also define a template as a BLOCK within the same file and PROCESS it just like any other template file. This can be invaluable for building up repetitive elements such as tables, menus, etc.: [% BLOCK tabrow %]
<tr><td>[% name %]</td><td>[% email %]</td></tr>; [% END %]; <table>
[% PROCESS tabrow name="tom" email="tom@here.org"; %]
[% PROCESS tabrow name="dick" email="disk@there.org"; %]
[% PROCESS tabrow name="larry" email="larry@where.org"; %]
</table>
Data and Code Binding
One of the key features that sets the Template Toolkit apart from other template processors is the ability to bind template variables to any kind of Perl data: scalars, lists, hash arrays, sub-routines and objects.: my $vars = {
root => 'http://here.com/there',
menu => [ 'modules', 'authors', 'scripts' ],
client => {
name => 'Doctor Joseph von Satriani',
id => 'JVSAT',

},
checkout => sub { my $total = shift; ...; return

$something },
shopcart => My::Cool::Shopping::Cart->new(),; };
The Template Toolkit will automatically Do The Right Thing to access the data in an appropriate manner to return some value which can then be output. The dot operator '.' is used to access into lists and hashes or to call object methods. The FOREACH directive is provided for iterating through lists, and various logical tests are available using directives such as IF, UNLESS, ELSIF, ELSE, SWITCH, CASE, etc.: [% FOREACH section = menu %]
<a href="[% root %]/[% section %]/index.html">[%

section %]</a>; [% END %]; <b>Client</a>: [% client.name %] (id: [% client.id %]); [% IF shopcart.nitems %]
Your shopping cart contains the following items:
<ul>
[% FOREACH item = shopcart.contents %]
<li>[% item.name %] : [% item.qty %] @ [%

item.price %]

[% END %]
</ul>

[% checkout(shopcart.total) %]; [% ELSE %]
No items currently in shopping cart.; [% END %]
Advanced Features: Filters, Macros, Exceptions, Plugins
The Template Toolkit also provides a number of additional directives for advanced processing and programmatical functionality. It supports output filters (FILTER), allows custom macros to be defined (MACRO), has a fullyfeatured exception handling system (TRY, THROW, CATCH, FINAL) and supports a plugin architecture (USE) which allows special plugin modules and even regular Perl mod ules to be loaded and used with the minimum of fuss. The Template Toolkit is "just" a template processor but you can trivially extend it to incorporate the functionality of any Perl module you can get your hands on. Thus, it is also a scalable and extensible template framework, ideally suited for managing the presentation layer for application servers, content management systems and other web applica tions.
Separating Presentation and Application Logic
Rather than embedding Perl code or some other scripting language directly into template documents, it encourages you to keep functional components (i.e. Perl code) sepa rate from presentation components (e.g. HTML templates). The template variables provide the interface between the two layers, allowing data to be generated in code and then passed to a template component for displaying (pipeline model) or for sub-routine or object references to be bound to variables which can then be called from the template as and when required (callback model).
The directives that the Template Toolkit provide implement their own mini programming language, but they're not really designed for serious, general purpose programming. Perl is a far more appropriate language for that. If you embed application logic (e.g. Perl or other scripting lan guage fragments) in HTML templates then you risk losing the clear separation of concerns between functionality and presentation. It becomes harder to maintain the two ele ments in isolation and more difficult, if not impossible, to reuse code or presentation elements by themselves. It is far better to write your application code in separate Perl modules, libraries or scripts and then use templates to control how the resulting data is presented as output. Thus you should think of the Template Toolkit language as a set of layout directives for displaying data, not calcu lating it.
Having said that, the Template Toolkit doesn't force you into one approach or the other. It attempts to be prag matic rather than dogmatic in allowing you to do whatever best gets the job done. Thus, if you enable the EVAL_PERL option then you can happily embed real Perl code in your templates within PERL ... END directives.
Performance
The Template Toolkit uses a fast YACC-like parser which compiles templates into Perl code for maximum runtime efficiency. It also has an advanced caching mechanism which manages in-memory and on-disk (i.e. persistent) ver sions of compiled templates. The modules that comprise the toolkit are highly configurable and the architecture around which they're built is designed to be extensible. The Template Toolkit provides a powerful framework around which content creation and delivery systems can be built while also providing a simple interface through the Tem plate front-end module for general use.

AUTHOR

Andy Wardley <abw@andywardley.com>

<http://www.andywardley.com/|http://www.andywardley.com/>

VERSION

Template Toolkit version 2.08, released on 30 July 2002.

COPYRIGHT

Ltd.
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

docs.sk