1Template::Manual::IntroU(s3e)r Contributed Perl DocumentaTteimopnlate::Manual::Intro(3)
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6 Template::Manual::Intro - Introduction to the Template Toolkit
7
9 The Template Toolkit is a collection of Perl modules which implement a
10 fast, flexible, powerful and extensible template processing system. It
11 is most often used for generating dynamic web content, although it can
12 be used equally well for processing any kind of text documents.
13 At the simplest level it provides an easy way to process template
15 files, filling in embedded variable references with their equivalent
16 values. Here's an example of a template.
17 Dear [% name %],
19 It has come to our attention that your account is in
21 arrears to the sum of [% debt %].
22 Please settle your account before [% deadline %] or we
24 will be forced to revoke your Licence to Thrill.
25 The Management.
27 By default, template directives are embedded within the character
29 sequences "[%" ... "%]" but you can change these and various other
30 options to configure how the Template Toolkit looks, feels and works.
31 You can set the "INTERPOLATE" option, for example, if you prefer to
32 embed your variables in Perl style:
33 Dear $name,
35 It has come to our attention that your account is in
37 arrears to the sum of $debt.
38 ...etc...
40
42 The Template Perl module is the front end to the Template Toolkit for
43 Perl programmers, providing access to the full range of functionality
44 through a single module with a simple interface. It loads the other
45 modules as required and instantiates a default set of objects to handle
46 subsequent template processing requests. Configuration parameters may
47 be passed to the Template constructor method, new(), which are then
48 used to configure the generate object.
49 use Template;
51 my $tt = Template->new({
53 INCLUDE_PATH => '/usr/local/templates',
54 INTERPOLATE => 1,
55 }) || die "$Template::ERROR\n";
56 The Template object implements a process() method for processing
58 template files or text. The name of the input template (or various
59 other sources) is passed as the first argument, followed by a reference
60 to a hash array of variable definitions for substitution in the
61 template.
62 my $vars = {
64 name => 'Count Edward van Halen',
65 debt => '3 riffs and a solo',
66 deadline => 'the next chorus',
67 };
68 $tt->process('letters/overdrawn', $vars)
70 || die $tt->error(), "\n";
71 The process() method returns a true value (1) on success and prints the
73 template output to "STDOUT", by default. On error, the process() method
74 returns a false value ("undef"). The error() method can then be called
75 to retrieve details of the error.
76
78 A number of special directives are provided, such as "INSERT",
79 "INCLUDE" and "PROCESS", which allow content to be built up from
80 smaller template components. This permits a modular approach to
81 building a web site or other content repository, promoting reusability,
82 cross-site consistency, ease of construction and subsequent
83 maintenance. Common elements such as headers, footers, menu bars,
84 tables, and so on, can be created as separate template files which can
85 then be processed into other documents as required. All defined
86 variables are inherited by these templates along with any additional
87 "local" values specified.
88 [% PROCESS header
90 title = "The Cat Sat on the Mat"
91 %]
92 [% PROCESS menu %]
94 The location of the missing feline has now been established.
96 Thank you for your assistance.
97 [% INSERT legal/disclaimer %]
99 [% PROCESS footer %]
101 You can also define a template as a BLOCK within the same file and
103 PROCESS it just like any other template file. This can be invaluable
104 for building up repetitive elements such as tables, menus, etc.
105 [% BLOCK tabrow %]
107 <tr><td>[% name %]</td><td>[% email %]</td></tr>
108 [% END %]
109 <table>
111 [% PROCESS tabrow name="tom" email="tom@here.org" %]
112 [% PROCESS tabrow name="dick" email="disk@there.org" %]
113 [% PROCESS tabrow name="larry" email="larry@where.org" %]
114 </table>
115
117 One of the key features that sets the Template Toolkit apart from other
118 template processors is the ability to bind template variables to any
119 kind of Perl data: scalars, lists, hash arrays, sub-routines and
120 objects.
121 my $vars = {
123 root => 'http://here.com/there',
124 menu => [ 'modules', 'authors', 'scripts' ],
125 client => {
126 name => 'Doctor Joseph von Satriani',
127 id => 'JVSAT',
128 },
129 checkout => sub { my $total = shift; ...; return $something },
130 shopcart => My::Cool::Shopping::Cart->new(),
131 };
132 The Template Toolkit will automatically Do The Right Thing to access
134 the data in an appropriate manner to return some value which can then
135 be output. The dot operator '"."' is used to access into lists and
136 hashes or to call object methods. The "FOREACH" directive is provided
137 for iterating through lists, and various logical tests are available
138 using directives such as "IF", "UNLESS", "ELSIF", "ELSE", "SWITCH",
139 "CASE", etc.
140 [% FOREACH section = menu %]
142 <a href="[% root %]/[% section %]/index.html">[% section %]</a>
143 [% END %]
144 <b>Client</b>: [% client.name %] (id: [% client.id %])
146 [% IF shopcart.nitems %]
148 Your shopping cart contains the following items:
149 <ul>
150 [% FOREACH item = shopcart.contents %]
151 <li>[% item.name %] : [% item.qty %] @ [% item.price %]
152 [% END %]
153 </ul>
154 [% checkout(shopcart.total) %]
156 [% ELSE %]
158 No items currently in shopping cart.
159 [% END %]
160
162 The Template Toolkit also provides a number of additional directives
163 for advanced processing and programmatical functionality. It supports
164 output filters (FILTER), allows custom macros to be defined (MACRO),
165 has a fully-featured exception handling system (TRY, THROW, CATCH,
166 FINAL) and supports a plugin architecture (USE) which allows special
167 plugin modules and even regular Perl modules to be loaded and used with
168 the minimum of fuss. The Template Toolkit is "just" a template
169 processor but you can trivially extend it to incorporate the
170 functionality of any Perl module you can get your hands on. Thus, it
171 is also a scalable and extensible template framework, ideally suited
172 for managing the presentation layer for application servers, content
173 management systems and other web applications.
174
176 Rather than embedding Perl code or some other scripting language
177 directly into template documents, it encourages you to keep functional
178 components (i.e. Perl code) separate from presentation components (e.g.
179 HTML templates). The template variables provide the interface between
180 the two layers, allowing data to be generated in code and then passed
181 to a template component for displaying (pipeline model) or for sub-
182 routine or object references to be bound to variables which can then be
183 called from the template as and when required (callback model).
184 The directives that the Template Toolkit provide implement their own
186 mini programming language, but they're not really designed for serious,
187 general purpose programming. Perl is a far more appropriate language
188 for that. If you embed application logic (e.g. Perl or other scripting
189 language fragments) in HTML templates then you risk losing the clear
190 separation of concerns between functionality and presentation. It
191 becomes harder to maintain the two elements in isolation and more
192 difficult, if not impossible, to reuse code or presentation elements by
193 themselves. It is far better to write your application code in
194 separate Perl modules, libraries or scripts and then use templates to
195 control how the resulting data is presented as output. Thus you should
196 think of the Template Toolkit language as a set of layout directives
197 for displaying data, not calculating it.
198 Having said that, the Template Toolkit doesn't force you into one
200 approach or the other. It attempts to be pragmatic rather than
201 dogmatic in allowing you to do whatever best gets the job done. Thus,
202 if you enable the EVAL_PERL option then you can happily embed real Perl
203 code in your templates within PERL ... END directives.
204
206 The Template Toolkit uses a fast YACC-like parser which compiles
207 templates into Perl code for maximum runtime efficiency. It also has
208 an advanced caching mechanism which manages in-memory and on-disk (i.e.
209 persistent) versions of compiled templates. The modules that comprise
210 the toolkit are highly configurable and the architecture around which
211 they're built is designed to be extensible. The Template Toolkit
212 provides a powerful framework around which content creation and
213 delivery systems can be built while also providing a simple interface
214 through the Template front-end module for general use.
215perl v5.32.0 2020-07-28 Template::Manual::Intro(3)