OVERVIEW

The Template Toolkit is a collection of Perl modules which collectively implement a fast and powerful template processing system. In this context, a template is a text document which contains embedded processing "directives". These instruct the template processor to perform certain actions such as; inserting the value of a variable, processing and including another template file or user-defined block, iterating through a set of values, and so on. Anything not marked as a template directive is treated as plain text and gets passed through unaltered. Directive are by default embedded like this: [% directive %]

The "mini-language" that the toolkit uses (ATML - A Template Markup Language :-) is designed to be clear, concise, regular in structure and simple in syntax. It is a specialised language which boasts many powerful features for constructing dynamic content but it is not a general purpose programming language. Instead, it supports a plugin interface which allows separate modules of application specific code to be written in the language of choice (i.e. Perl, C, C++) and then loaded, used and re-used as required.

In other words, it helps to promote the separation of application code (the implementation) from the user interface (the presentation). It tries to keep templates clutter-free, concentrating on what the document looks like, not how the various items of content are stored, retrieved or calculated. From the perspective of a web designer, for example, they're just bits of text that get inserted into different parts of the page.

Development and subsequent maintenance become easier and less error-prone when the "back-end" is separated from the "front-end". As a further benefit, it becomes far easier to re-use plugin code by simply changing the templates that generate the output. Likewise it becomes possible to change the implementation of some functionality without affecting the template files.

Application code becomes easier to write and more portable when you don't have to worry about what the output looks like. From the perspective of the coder, this is a Good Thing. They only have to worry about performing some task and returning some value and really don't care if it ends up right-justified in a table with an blue background. Similarly, the output templates become easier to write and more portable because they don't contain any implementation specific details (i.e. code).

The end result is that complex, dynamic content systems can be built easily and quickly from a number of small, reusable components. Some of these components are template files representing user interface "chunks" and others may be data structures, library code, user-defined sub-routines or objects that implement various functionalities of the system. The Template Toolkit's role is to help glue the different pieces together as quickly and simply as possible, hiding as many of the unnecessary details as possible.

The Template Toolkit is ideally suited for generating web content, but it is by no means limited or specific to this or any other application area. The plugin interface means that it doesn't have to be - it can just concentrate on the task of constructing documents and doesn't care if you subsequently use it to generate HTML, LaTeX, RTF or plain text documents from a command-line, CGI script or an in-server web process such as Apache/mod_perl using data extracted from a CGI form, a database, by psychic medium or by averaging last month's rainfall in Seattle. You choose what do to with it and how to do it. Simply load additional functionality as you need it from CPAN modules, Template Toolkit plugins, generic web applications such as chat rooms, FAQ lists, bulletin boards, etc., or any other code you can beg, borrow or write yourself.

The philosophy behind the toolkit should hopefully now be clearer. It is about power and ease of use in document construction and defers the task of any application-specific functionality to a far more powerful, general purpose language - Perl. The Template Toolkit promotes a clean separation between the two for the reasons outlined above. It is important to note, however, that no one tool is appropriate for every use and there are many times when you can't beat simply embedding Perl code directly into your document. In those cases, Mark-Jason Dominus' Text::Template module comes highly recommended (available from CPAN).

The Template Toolkit is a direct descendant of, and replacement for the Text::MetaText module. It has been designed and rebuilt from scratch based on several years of experience gained from developing, supporting and using Text::MetaText and other template processing applications and tools. It is an Open Source project in which contribution and collaboration are encouraged.