HTML::Chunks - A simple nested template engine for HTML, XML and XHTML




This class implements a simple text-based template engine, originally intented to allow web applications to completely separate layout HTML from programming logic. However, the engine is flexible enough to be applied to other text-based situations where templates are helpful, such as generating email messages, XML data files, etc.


 my $engine = new HTML::Chunks(@chunkFiles);

 $engine->addChunk($smallChunk, \$hugeChunk);
 $engine->addNamedChunk('myChunk', $chunk);
 $engine->output('myChunk', {
   firstName => 'Homer',
   lastName => 'Simpson',
   meals => \&outputMeals
 }, @extraData);

 my @names = $engine->getChunkNames();
 my $chunk = $engine->getChunk('myChunk');
 my $oldValue = $engine->setCrush(0);


This template engine is based upon "chunks", which are merely named chunks of textual information such as HTML. Each chunk may be individually addressed by an application to produce output. A chunk definition may also contain data elements which will be replaced with dynamic data at runtime. A simple chunk definition looks like:

 <!-- BEGIN meal -->
 <!-- END -->

This defines a chunk named meal. This chunk contains two data elements named date and food. These will both be replaced with real data by the application at runtime. The leading and trailing ## characters simply identify them as data elements and are not part of the actual names.

Chunk definitions can even be embedded within one another. It's possible (and recommended!) to construct a definition file as a full HTML file that you can preview in a web browser. Embedding one chunk definition within another does not imply any association or positional placement between the two chunks. Things would turn out the same if you put the definitions in a straight list, one after another. Embedding is just a cool formatting convenience that you can choose to take advantage of -- or not.

You may optionally surround a data element with HTML comment characters so it won't show up when previewing a chunk file in a browser. For this to work, the data element must be the only thing in the comment, such as:

 <!-- ##data## -->

The entire comment will be replaced with the data value at run time, so the resulting data will NOT be within a comment.

See the EXAMPLES section below for a sample.


my $engine = new HTML::Chunks(@files);

Constructs a new chunk engine object and reads any supplied chunk files.


Reads the specified chunk definition files.


Reads chunk definitions from an alternate simpler file format. This should only be used for defining very short chunks with minimal HTML. It comes in very handy for small configuration elements. The format allows one definition per line, with each line containing the chunk name followed by any amount of whitespace followed by the chunk definition.

For example:

  errorMsg    Awooga!  Something has gone haywire!

Defines new chunks according to the definitions contained in the supplied list. Each member of the list must hold at least one full chunk definition, complete with BEGIN/END statements. The list may contain simple string scalars or references to scalars. References are handy if you have a large chunk loaded and wish to conserve memory.

$engine->addNamedChunk($name, $chunk);

Defines a new chunk named $name. The chunk definition contained in $chunk does not need the outer set of BEGIN/END statements since the name is already specified. This comes in handy when you are reading chunk definitions from a database column and don't want to bother with redundant embedded BEGIN/END statements for each row. $chunk may be either a scalar or reference to a scalar. References are handy if you have a large chunk loaded and wish to conserve memory.

my @names = $engine->getChunkNames();

Returns a list of defined chunk names.

my $chunk = $engine->getChunk($name);

Returns the body of a defined chunk named $name. You rarely need to do this, and we strongly discourage bypassing the output routine and printing the chunk body directly. However, this can come in handy on occasion. For example, you might write a utility that lets the engine load/parse chunk definitions and then inserts them individually into a database.

$engine->output($name, \%data, @extraInfo);

Outputs the body of the chunk named $name to the currently selected filehandle. The %data hash is used to expand any data elements encountered in the chunk. The keys in %data should be the data element names without the leading and trailing ## characters. The hash values are either simple scalars containing a data value or a subroutine reference. For example:

 $engine->output('chunk', {
   firstName => 'Homer',
   lastName => 'Simpson',
   meals => \&outputMeals
 }, $userID);  

When the engine encouters the meals data element, it will call the outputMeals subroutine. outputMeals would then be responsible for outputting the data for data element meals, preferably by performing some snazzy logic and then outputting another chunk.

Every data subroutine is called by the engine in the following way:

 dataRoutine($engine, $elementName, @extraInfo);

So, the outputMeals example above would be invoked as:

 outputMeals($engine, 'meals', $userID);
my $oldValue = $engine->setCrush(0);

Sets whether the engine crushes whitespace within chunks or not. Accepts one parameter that is treated as a boolean (true/false). The default is on, which is recommended for HTML applications. If you are using chunks for something whitespace sensitive like email generation, you should turn this off to have chunks output exactly as they are defined.

my $oldValue = $engine->setCascade(0);

Sets whether or not the engine lets data cascade into nested calls to output. For instance, if you output a chunk from within a data element handling routine, any data that was defined for the parent chunk will also be available to the chunk currently being output. If that doesn't make sense, don't worry about it. It's rare that you'd want to turn this behavior off. This setting is enabled by default.


Complete separation of code and layout is fairly new to most people, and the chunky way of life does require a little shift in your thinking. However, once you dig it, this can be a very powerful and productive way to develop. A more complete example might help you get there.

Consider the following chunk definition:

 <!-- begin mealPage -->
   <title>Meal List</title>
   <h1>Meal List for ##firstName##</h1>

   <table border="1">

     <!-- ##meals## -->

     <!-- BEGIN meal -->
     <!-- END meal -->


 <!-- end MealPage -->

Let's say this were in a file called meals.html. Because we embedded some chunk definitions within others, you could actually view it in a web browser and get a preview of things to come. Again, embedding one definition within another means nothing. It is simply a formatting convenience to let you construct chunk definition files that are also valid HTML files.

Now, a fairly small (but commented) script to do something with it:

 use HTML::Chunks;
 use strict;
 # create a new engine and read our chunk definitions
 my $engine = new HTML::Chunks('meals.html');
 # output the main 'mealPage' chunk.  name information
 # is supplied with static text.  the 'meals' data element
 # is handled by the 'outputMeals' routine.
 $engine->output('mealPage', {
   firstName => 'Homer',
   lastName => 'Simpson',
   meals => \&outputMeals
 # our first data element routine
 sub outputMeals
   my ($engine, $element) = @_;
   # normally you would read this from a database but
   # this is easier for an example.
   my @meals = (
     [ '2001-09-09 08:15', 'One dozen assorted donuts' ],
     [ '2001-09-09 11:45', 'One giant sub sandwich' ],
     [ '2001-09-09 14:22', 'One bag of gummy worms' ],
     [ '2001-09-09 18:34', 'Bucket of BBQ' ]
   # we output each meal using the 'meal' chunk.  simple.
   foreach my $meal (@meals)
     $engine->output('meal', {
       date => $meal->[0],
       food => $meal->[1]


For the adventurous, there is HTML::Chunks::Super, a subclass of HTML::Chunks with enhanced features.


Created, developed and maintained by Mark W Blythe and Dave Balmer, Jr. Contact or for comments or questions.


(C)2001-2009 Mark W Blythe and Dave Balmer Jr, all rights reserved. This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.