NAME

Text::MagicTemplate - magic merger of runtime values with templates

VERSION 3.03

WARNING!

Versions > 3.0 are a complete new rewriting of the 2.xx code. Although the effort to maintain backward compatibility, some little but critical changes that could break your old code have been introduced.

You can maintain your old applications whether adapting them to the new style (very easy job to do), or using an older compatible version (I hate this way :-(). See Warning and History files in this distribution for details.

SYNOPSIS

Just add these 2 magic lines to your code...

use Text::MagicTemplate;
Text::MagicTemplate->print( '/path/to/template' );

to have all your variable and subroutines merged with the template file, or set one or more constructor array to customize the output generation as you need:

use Text::MagicTemplate;

$mt = new Text::MagicTemplate
          markers         =>   qw( < / > )                     ,
          lookups         => [ \%my_hash, $my_obj, 'main'    ] ,
          zone_handlers   => [ \&my_zone_handler, '_EVAL_'   ] ,
          value_handlers  => [ 'DEFAULT', \&my_value_handler ] ,
          text_handlers   =>   sub {print lc $_[1]}            ,
          output_handlers =>   sub {print uc $_[1]}            ,
          post_handlers   =>   \&my_post_handler               ;

$mt->print( '/path/to/template' );

DESCRIPTION

Text::MagicTemplate is a "magic" interface between programming and design. It makes "magically" available all the runtime values - stored in your variables or returned by your subroutines - inside a static template file. In simple cases there is no need to assign values to the object. Template outputs are linked to runtime values by their identifiers, which are added to the template in the form of simple labels or blocks of content.

a label: {identifier}
a block: {identifier} content of the block {/identifier}

From the designer point of view, this makes things very simple. The designer has just to decide what value and where to put it. Nothing else is required, no complicated new syntax to learn!

On the other side, the programmer has just to define variables and subroutines as usual and their values will appear in the right place within the output. The automatic interface allows the programmer to focus just on the code, saving him the hassle of interfacing code with output, and even complicated output - with complex switch branching and nested loops - can be easily organized by minding just a few simple concepts.

How it works

The object parse the template and search for any labeled zone
When a zone is found, the object looks into your code and search for any variable or sub with the same identifier (name)
When a match is found the object replace the label or the block with the value returned by the variable or sub found into your code (dereferencing and/or executing code as needed). (see "Understand the output generation" for details)

Simple example

The following is a very simple example only aimed to better understand how it works: obviously, the usefulness of Text::MagicTemplate comes up when the output become more complex.

Imagine you need an output that looks like this template file:

City: {city}
Date and Time: {date_and_time}

where {city} and {date_and_time} are just placeholder that you want to be replaced in the output by some real runtime values. Somewhere in your code you have defined a scalar and a sub to return the 'city' and the 'date_and_time' values:

$city = 'NEW YORK';
sub date_and_time { localtime }

you have just to add these 2 magic lines to the code:

use Text::MagicTemplate;
Text::MagicTemplate ->print( 'my_template_file' );

to generate this output:

City: NEW YORK
Date and Time: Sat Nov 16 21:03:31 2002

With the same 2 magic lines of code, Text::MagicTemplate can automatically look up values from scalars, arrays, hashes, references and objects from your code and produce very complex outputs. The default settings are usually smart enough to do the right job for you, however if you need complete control over the output generation, you can fine tune them by controlling them explicitly. See "CUSTOMIZATION" for details.

More complex example

the template

The template file 'my_template_file'... (this example uses plain text for clarity, but MagicTemplate works with any type of text file)

A scalar variable: {a_scalar}.
A reference to a scalar variable: {a_ref_to_scalar}.
A subroutine: {a_sub}
A reference to subroutine: {a_ref_to_sub}
A reference to reference: {a_ref_to_ref}
A hash: {a_hash}this block contains a {a_scalar} and a {a_sub}{/a_hash}

A loop:{an_array_of_hashes}
Iteration #{ID}: {guy} is a {job}{/an_array_of_hashes}

An included file:
{'my_included_file'}

... and another template file F<'my_included_file'>
that will be included...

this is the included file 'my_included_file'
that contains a label: {a_scalar}

the code

... some variables and subroutines already defined somewhere in your code...

$a_scalar           = 'THIS IS A SCALAR VALUE';
$a_ref_to_scalar    = \$a_scalar;
@an_array_of_hashes = ( { ID => 1, guy => 'JOHN SMITH',  job => 'PROGRAMMER' },
                        { ID => 2, guy => 'TED BLACK',   job => 'WEBMASTER' },
                        { ID => 3, guy => 'DAVID BYRNE', job => 'MUSICIAN' }  );
%a_hash             = ( a_scalar => 'NEW SCALAR VALUE'
                        a_sub    => sub { 'NEW SUB RESULT' } );

sub a_sub         { 'THIS SUB RETURNS A SCALAR' }
sub a_ref_to_sub  { \&a_sub }
sub a_ref_to_ref  { $a_ref_to_scalar }

Just add these 2 magic lines...

use Text::MagicTemplate;
Text::MagicTemplate->print( 'my_template_file' );

the output

(in this example Lower case are from templates and Upper case are from code):

A scalar variable: THIS IS A SCALAR VALUE.
A reference to a scalar variable: THIS IS A SCALAR VALUE.
A subroutine: THIS SUB RETURNS A SCALAR
A reference to subroutine: THIS SUB RETURNS A SCALAR
A reference to reference: THIS IS A SCALAR VALUE
A hash: this block contains a NEW SCALAR VALUE and a NEW SUB RESULT

A loop:
Iteration #1: JOHN SMITH is a PROGRAMMER
Iteration #2: TED BLACK is a WEBMASTER
Iteration #3: DAVID BYRNE is a MUSICIAN

An included file:
this is the included file 'my_included_file'
that contains a label: THIS IS A SCALAR VALUE.

Policy

The main principle of Text::MagicTemplate is: keep the designing separated from the coding, giving all the power to the programmer and letting designer do only design. In other words: while the code includes ALL the active and dynamic directions to generate the output, the template is a mere passive and static file, containing just placeholder (zones) that the code will replace with real data.

This philosophy keep both jobs very tidy and simple to do, avoiding confusion and enforcing clearness, specially when programmer and designer are 2 different people. But another aspect of the philosophy of Text::MagicTemplate is flexibility, something that gives you the possibility to easily bypass the rules.

Even if I don't encourage breaking the main principle (keep the designing separated from the coding), sometimes you might find useful to put inside a template some degree of perl code, or may be you want just to interact DIRECTLY with the content of the template. See "Use subroutines to rewrite links" and "Embed perl into a template" for details.

Other important principles of Text::MagicTemplate are scalability and expandability. The whole extension system is built on these principles, giving you the possibility of control the behaviour of this module by omitting, changing the orders and/or adding your own handlers, without the need of subclassing the module. See "CUSTOMIZATION".

Features

Since syntax and coding related to this module are very simple and mostly automatic, you should careful read this section to have the right idea about its features and power. This is a list - with no particular order - of the most useful features and advantages:

Simple, flexible and powerful to use

In simple cases, you will have just to use new() and print(template) methods, without having to pass any other value to the object: it will do the right job for you. However you can fine tune the behaviour as you need.
Extremely simple and configurable template syntax

The template syntax is so simple and code-independent that even the less skilled webmaster will manage it without bothering you :-). By default Text::MagicTemplate recognizes labels in the form of simple identifiers surrounded by braces ({my_identifier}), but you can easily use different markers (see "Redefine Markers").
Automatic or manual lookup of values

By default, Text::MagicTemplate compares any label identifier defined in your template with any variable or subroutine identifier defined in the caller namespace. However, you can explicitly define the lookup otherwise, by passing a list of package namespaces, hash references and blessed objects to the lookups constructor array.
Unlimited nested included templates

Sometimes it can be useful to split a template into differents files. No nesting limit when including files into files. (see "Include a file")
Branching

You can easily create simple or complex if-elsif-else conditions to print just the blocks linked with the true conditions (see "Setup an if-else condition" and "Setup a switch condition")
Unlimited nested loops

When you need complex outputs you can build any immaginable nested loop, even mixed with control switches and included templates (see "Build a loop" and "Build a nested loop")
Scalable and expandable extensions system

You can load only the handlers you need, to gain speed, or you can add as many handlers you will use, to gain features. You can even write your own extension handler in just 2 or 3 lines of code, expanding its capability for your own purpose. (see new() method )
Perl embedding

Even if I don't encourage this approach, however you can very easily embed any quantity of perl code into any template. (see "Embed perl into a template")
Block management

When you need complex management of templates files, you have a couple of static methods to extract, mix and set blocks inside any template. (see get_block() and set_block() methods)
Placeholders and simulated areas

Placeholders and simulated areas can help in designing the template for a more consistent preview of the final output. (see "Setup placeholders" and "Setup simulated areas")
Labels and block list

When you have to deal with a webmaster, you can easily print a pretty formatted output of all the identifiers present in a template. Just add your description of each label and block and save hours of explanations ;-) (see ID_list() static method)
Simple to maintain

Change your code and Text::MagicTemplate will change its behaviour accordingly. In most cases you will not have to reconfigure, either the object, or the template.
Small footprint

The MagicTemplate system doesn't use any other module and its code (including all the standard and autoloaded handlers) is just about 300 lines of pure perl (easier to write that this documentation :-) ). You don't need any compiler in order to install it on any platform.

INSTALLATION

Prerequisites

Perl version >= 5.005

CPAN

If you want to install Text::MagicTemplate plus all related extensions (HTML::MagicTemplate and prerequisites), all in one easy step:

perl -MCPAN -e 'install Bundle::Text::MagicTemplate'

Standard installation

From the directory where this file is located, type:

perl Makefile.PL
make
make test
make install

Note: this installs just the main distribution and does not install HTML::MagicTemplate and its prerequisites.

Structure

Bundle::Text::MagicTemplate  a bundle to install everything in one step
Text::MagicTemplate          the main module
Text::MagicTemplate::Zone    defines the zone object
HTML::MagicTemplate          handlers useful in HTML environment

Uninstallation of obsolete modules

If you have installed some 2.xx version you could want to uninstall the obsolete files from that installation. You should manually unlink (delete) the following files and directories (sorry, no automatic uninstallation yet):

Text/MagicTemplate/Tutorial.pm
Text/MagicTemplate/Utilities.pm
Text/MagicTemplateX.pm
Text/MagicTemplateX directory including all its content

METHODS

new ( [constructor_arrays] )

If you use just the defaults, you can construct the new object by writing this:

$mt = new Text::MagicTemplate ;

If you use the defaults, and you have just to print a template, you can use the print() method as a static method, completely avoiding the new() method:

use Text::MagicTemplate;
Text::MagicTemplate->print('template');

If you don't pass any parameter to the constructor method, the constructor defaults are usually smart enough to do the right job for you, but if you need complete control over the output generation, you can fine tune it by controlling it explicitly. (see the section "Constructor Arrays").

output ( template [, identifier] )

This method merges the runtime values with the template and returns a reference to the output. It accepts one template parameter that can be a reference to a SCALAR content, a path to a template file or a filehandle. If any identifier is passed, it returns a reference to the output of just that block.

# template is a path
$output = $mt->output( '/temp/template_file.html' ) ;

# template is a reference
$output = $mt->output( \$tpl_content ) ;

#template is a filehandler
$output = $mt->output( *FILEHANDLER );

# this limits the output to just 'my_block_identifier'
$my_block_output = $mt->output( \$tpl_content, 'my_block_identifier');

print ( template [, identifier] )

This method merges the runtime values with the template and prints the output. It accepts one template parameter that can be a reference to a SCALAR content, a path to a template file or a filehandle. If any identifier is passed, it prints the output of just that block.

# template is a path
$mt->print( '/temp/template_file.html' );

# template is a reference
$mt->print( \$tpl_content ) ;

#template is a filehandler
$mt->print( *FILEHANDLER );

# this limits the output to just 'my_block_identifier'
$mt->print( \$tpl_content, 'my_block_identifier' );

You can use the print() method as a static method as well. The static method accepts the same parameters. It constructs a default object internally and prints the merged output.

Text::MagicTemplate->print( 'template' );

# that explicitly means
$mt = Text::MagicTemplate->new;
$mt->print( 'template' );

get_block ( template [, identifier] )

This method returns a reference to the template content or to a block inside the template, without merging values. It accepts one template parameter that can be a reference to a SCALAR content, a path to a template file or a filehandle. If any identifier is passed, it returns just that block.

# this returns a ref to the whole template content
$tpl_content = $mt->get_block ( '/temp/template_file.html' );

# this return a ref to the 'my_block_identifier' block
$tpl_block = $mt->get_block ( '/temp/template_file.html',
                              'my_block_identifier'     );

# same thing passing a reference
$tpl_block = $mt->get_block ( $tpl_content          ,
                              'my_block_identifier' );

set_block ( template, identifier, new_content )

This method sets the content of the block (or blocks) identifier inside a template - without merging values - and returns a reference to the changed template. It accepts one template parameter that can be a reference to a SCALAR content, a path to a template file or a filehandle. New_content can be a reference to the content or the content itself.

# this return a ref to the 'my_block' block
$new_content = $mt->get_block ( '/temp/template_file_2.html',
                                'my_block'                  );

# this returns a ref to the changed template content,
$changed_content = $mt->set_block ( '/temp/template_file.html',
                                    'my_old_block'            ,
                                     $new_content             );

STATIC METHODS

ID_list ( [identation_string [, end_marker]] )

Calling this method (before the output() or print() methods) will redefine the behaviour of the module, so your program will print a pretty formatted list of only the identifiers present in the template, thus the programmer can pass a description of each label and block within a template to a designer.

The method accepts an 'identation string' (usually a tab character or a few spaces), that will be used to ident nested blocks. If you omit the identation string 4 spaces will be used. The method accept also as second parameter a 'end marker string, tat is used to distinguish the end label in a container block. If you omit this a simple '/' will be used.

# defalut
Text::MagicTemplate->ID_list;

# custom identation
Text::MagicTemplate->ID_list("\t", '#');

CUSTOMIZATION

Note: You can completely skip this section if you plan to use just the defaults.

The output generation can be completely customized during the creation of the new object by passing to the new() method one or more "Constructor Arrays".

Constructor Arrays

The new() method accepts one optional reference to a hash that can contain the following optionals constructor arrays:

markers
lookups
zone_handlers
value_handlers
value_handlers
text_handlers
post_handlers

Constructor Arrays are array references containing elements that can completely change the behaviour of the object and even add code not directly related with the output generation but executed during the process.

All the constructor arrays should be array references, but if you have to pass just one element, you can pass it as a plain element as well:

$mt = new Text::MagicTemplate
          lookups => [\%my_hash] ,
          markers => ['HTML'   ] ;

# same thing less noisy
$mt = new Text::MagicTemplate
          lookups => \%my_hash ,
          markers => 'HTML'    ;

All the handlers in -*_handlers (zone handlers, value handlers, output handlers, text handlers, post handlers) receive the zone object as $_[0] parameter. Besides, the value handlers and the text handlers receive also the processed text as $_[1] parameter.

Note: to mantain backward compatibility, you can use the old constructor arrays identifiers with the prepended '-' and pass a reference to a hash:

# old style with '-flag' and brackets
$mt = new Text::MagicTemplate
          {
            -markers         =>   qw( < / > )                     ,
            -lookups         => [ \%my_hash, $my_obj, 'main'    ] ,
            -zone_handlers   => [ \&my_zone_handler, '_EVAL_'   ] ,
            -value_handlers  => [ 'DEFAULT', \&my_value_handler ] ,
            -text_handlers   =>   sub {print lc $_[1]}            ,
            -value_handlers =>   sub {print uc $_[1]}            ,
            -post_handlers   =>   \&my_post_handler               ,
          } ;

Note: Text::MagicTemplate internally handles these flags with the old style notation at the moment.

markers

Use this constructor array to define the 3 label markers - START_MARKER, END_MARKER_ID, END_MARKER - you want to use in your template. The markers constructor array can contain a name of "standard markers", or a reference to an array containing the 3 explicit markers.

If you want to use the default markers, just call the new() method without any markers constructor array:

# default markers
$mt = new Text::MagicTemplate;

# same but explicit extension name
$mt = new Text::MagicTemplate
          markers => 'DEFAULT';

# same but 3 explicit default markers
$mt = new Text::MagicTemplate
          markers => [ '{', '/', '}' ] ;

# HTML markers extension name
$mt = new Text::MagicTemplate
          markers => 'HTML' };

# same but 3 explicit HTML markers
$mt = new Text::MagicTemplate
          markers => [ qw( <!-- / --> ) ] ;

# custom explicit markers
$mt = new Text::MagicTemplate
          markers => [ qw( __ END_ __ ) ] ;

Since each element of the markers array is parsed as a regular expression as: qr/element/, you can extend the markers beyond a static string marker. This markers:

# 3 weird explicit markers
$mt = new Text::MagicTemplate
          markers => [ '\d{3}', '\W', '\d{3}' ];

will match this blocks labeled 'identifier':

235identifier690 content of block 563-identifier054
123identifier321 content of block 000#identifier865

standard markers

Text::MagicTemplate offers 2 standar markers: DEFAULT and HTML:

DEFAULT

The default markers:

START MARKER:  {
END_MARKER_ID: /
END_MARKER:    }

Example of block:

{identifier} content of the block {/identifier}

HTML

HTML-comment-like markers. If your output is a HTML text - or just because you prefer that particular look - you can use it instead of using the default markers.

START MARKER:  <!--{
END_MARKER_ID: /
END_MARKER:    }-->

Example of block:

<!--{identifier}--> content of the block <!--{/identifier}-->

Usage:

$mt = new Text::MagicTemplate
          markers => 'HTML' ;

The main advantages to use it are:

You can add labels and blocks and the template will still be a valid HTML file.
You can edit the HTML template with a WYSIWYG editor, keeping a consistent preview of the final output
The normal HTML comments will be preserved in the final output, while the labels will be wiped out.

If you want to use the HTML handlers too, you should install HTML::MagicTemplate. See HTML::MagicTemplate for details.

lookups

Use this constructor array to explicitly define where to look up the values in your code. This array can contain package names, blessed objects and hash references. If no lookups construction array is passed, the package namespace of the caller will be used by default.

With packages names the lookup is done with all the IDENTIFIERS (variables and subroutines) defined in the package namespace.

With blessed objects the lookup is done with all the IDENTIFIERS (variables and methods) defined in the class namespace. Note: Use this type of location when you want to call an object method from a template: the method will receive the blessed object as the first parameter and it will work as expected.

With hash references the lookup is done with the KEYS existing in the hash.

If you want to make available all the identifiers of your current package, just call the constructor without any lookups parameter:

# default lookup in the caller package
$mt = new Text::MagicTemplate ;

# same thing but explicit
$mt = new Text::MagicTemplate
          lookups => __PACKAGE__ ;

If you want to keep unavailable some variable or subroutine from the template, you can pass just the reference of some hash containing just the identifiers used in the template. This is the best method to use the module IF you allow untrustworthy people to edit the template AND if you have any potentially dangerous subroutine in your code. (see "Allow untrustworthy people to edit the template").

# lookup in %my_hash only
$mt = new Text::MagicTemplate
          lookups => \%my_hash ;

You can also define an arbitrary list of packages, references to hashes and blessed object as the lookup: the precedence of the lookup will be inherited from the order of the items passed, and the first found mach will return the value.

Note: If you have multiple symbols in your code that maches the label id in your template, don't expect any warning: to be fast, Text::MagicTemplate does not check your errors and consider OK the first symbol it founds.

# lookup in several locations
$mt = new Text::MagicTemplate
          lookups => [ \%my_hash, 'main', \%my_other_hash ] ;

In this example, the lookup will be done in %my_hash first - if unsuccessful - it will be done in the 'main' package and - if unsuccessful - it will be done in %my_other_hash.

If you use Text::MagicTemplate inside another module, you can pass the blessed object as the location:

use Text::MagicTemplate;
package Local::foo;
sub new
{
    my $s = bless {data=>'THE OBJECT DATA'}, shift;
    $s->{mt} = new Text::MagicTemplate
                   lookups => $s;
    $s;
}

sub method_triggered_by_lookup
{
    my $s = shift; # correct object passed
    ...
    $s->{data};
}

so that if some zone identifier will trigger 'method_triggered_by_lookup', it will receive the blessed object as the first parameter and it will work as expected.

zone_handlers

Use this constructor array to add handlers to manage the output generation before any other process (even before the lookup()). The zone handlers are executed just after the creation of the new zone, so you can even bypass or change the way of calling the other processes.

This constructor array can contain code references and/or standard zone handlers names (resulting in one or more code references: see "standard zone handlers" for details.

The default zone_handler is undefined, so you must add explicitly any standard zone handler or your own handler in order to use it.

$mt = new Text::MagicTemplate
          zone_handlers => [ '_EVAL_'           ,
                             '_EVAL_ATTRIBUTES' ,
                              \&my_handler      ] ;

standard zone handlers

_EVAL_

This handler sets the value property to the evalued result of the zone content when the zone identifier is equal to '_EVAL_'

WARNING: For obvious reasons you should use this zone handler ONLY if you are the programmer AND the designer.

This handler is useful if you want a cheap way to embed perl code in the template. (see "Embed perl into a template")

_EVAL_ATTRIBUTES_

This handler sets the param property to the evalued result of the zone attributes

WARNING: For obvious reasons you should use this zone handler ONLY if you are the programmer AND the designer.

This handler is useful if you want to pass some structure to a sub from the template without writing a parser: you will have the structure available in $z->param. (see "Pass a structure to a subroutine")

TRACE_DELETIONS

This handler generates a diagnostic output for each zone that has not generated any output. It will output a string like <my_zone_id not found> or <my_zone_id found but empty> in place of the zone, so you can better understand what's going on.

value_handlers

Use this constructor array to explicitly define or modify the way the object finds the value in your code.

This constructor array can contain code references and/or standard value handlers names (resulting in one or more code references: see "standard value handlers" for details.

If you don't pass any value_handler constructor array, the default will be used:

$mt = new Text::MagicTemplate;

# means
$mt = new Text::MagicTemplate
          value_handler => 'DEFAULT' ;

# that expicitly means
$mt = new Text::MagicTemplate
      value_handlers => [ qw( SCALAR REF CODE ARRAY HASH  ) ] ;

Where 'DEFAULT', 'SCALAR', 'REF', 'CODE', 'ARRAY', 'HASH' are standard value handlers names.

You can add, omit or change the order of the element in the array, fine tuning the behaviour of the object.

$mt = new Text::MagicTemplate
          value_handlers => [ 'DEFAULT', \&my_handler ] ;

# that explicitly means
$mt = new Text::MagicTemplate
          value_handlers => [ 'SCALAR','REF','CODE', 'ARRAY','HASH',
                              \&my_handler ] ;

# or you can add, omit and change the order of the handlers
$mt = new Text::MagicTemplate
          value_handlers => [ 'SCALAR','REF',\&my_handler,'ARRAY','HASH'] ;

standard value handlers

DEFAULT

This is the shortcut for the default collection of value handlers that defines the following handlers:

SCALAR
REF
CODE
ARRAY
HASH

All the default values are based on a condition that checks the found value.

SCALAR

A SCALAR value sets the output property to the value, and pass it to the output_process ending the value_process method.

REF

A REFERENCE value (SCALAR or REF) sets the value property to the dereferenced the value and start again the value_process() method

CODE

A CODE value sets the value property to the result of the execution of the code and start again the value_process() method. The subroutine will receive the zone object as a parameter.

If you want to avoid the execution of code, triggered by some identifier, just explicitly omit this handler

$mt = new Text::MagicTemplate
          value_handlers => [ qw( SCALAR REF ARRAY HASH ) ] ;

See "Avoid unwanted executions" for details. See also "Pass parameters to a subroutine"

ARRAY

This handler generates a loop, merging each value in the array with the zone content and replacing the zone with the sequence of the outputs. (see "Build a loop" and "Build nested a loop" for details).

HASH

A HASH value type will set that HASH as a temporary lookup for the zone. Text::MagicTemplate first uses that hash to look up the identifiers contained in the block; then, if unsuccessful, it will search into the other elements of the lookups constructor array. This handler is usually used in conjunction with the ARRAY handler to generate loops. (see "Build a loop" and "Build nested a loop" for details).

output_handlers

If you need to change the way the output is processed, you can add your own handler.

This constructor array can contain code references and/or standard value handlers names (resulting in one or more code references: see "standard output handlers" for details.

If you want to use the default output handler, just call the new() method without any output_handler constructor array:

$mt = new Text::MagicTemplate;

# this means (if you are using print() method)
$mt = new Text::MagicTemplate
          output_handler => 'DEFAULT_PRINT_HANDLER';

# or means (if you are using output() method)
$mt = new Text::MagicTemplate
          output_handler => 'DEFAULT_OUTPUT_HANDLER' ;

standard output handlers

DEFAULT_PRINT_HANDLER

This handler is set by default by the print() method. It receives and print each chunk of output that comes from the output generation.

This is the code of the print handler:

sub{ print $_[1] }

DEFAULT_OUTPUT_HANDLER

This handler is set by default by the output() method. It receives and stores in $s->{output} each chunk of output that comes from the output generation.

This is the code of the print handler:

sub{ $_[0]->mt->{output} .= $_[1] }

text_handlers

Use this constructor array only if you want to process the text coming from the template in a different way from the text coming from the code.

This constructor array can contain code references and/or standard output handlers names (resulting in one or more code references: see "standard output handlers" for details).

If you don't set any text handler, the current output handlers will be used.

post_handlers

Use this constructor array only if you want to clean up or log processes just before a zone is destroyed. (see also "post_process()" in Text::MagicTemplate::Zone)

Note: This constructor array can contain code references.

HOW TO...

This section is oriented to suggest you specific solutions to specific needs. If you need some more help, feel free to send me an e-mail to dd@4pro.net.

Understand the output generation

By default the output will be generated by the found value type, that means that differents value types will cause different behaviour in generating the output. In details:

A SCALAR value type will replace the zone with the scalar value.
A REFERENCE value will be dereferenced, and the value returned will be checked again to apply an appropriate behaviour
A CODE value type will be executed, and the value returned will be checked again to apply an appropriate behaviour
An ARRAY value type will generate a loop, merging each value in the array with the zone content and replacing the zone with the sequence of the outputs.
A HASH value type will set that HASH as a temporary lookup for the zone. Text::MagicTemplate first uses that hash to look up the identifiers contained in the block; then, if unsuccessful, it will search into the other elements of the lookups constructor array.
Finally, if no value are found in the code, the zone will be deleted.

These are spme examples of default value handlers:

The same template: '{block}|before-{label}-after|{/block}'

... with these values...               ...produce these outputs
------------------------------------------------------------------------
$label = 'THE VALUE';            >
$block = undef;
------------------------------------------------------------------------
$label = 'THE VALUE';            >  NEW CONTENT
$block = 'NEW CONTENT';
------------------------------------------------------------------------
$label = 'THE VALUE';            >  |before-THE VALUE-after|
$block = {};
------------------------------------------------------------------------
$label = undef;                  >  |before--after|
$block = {};
------------------------------------------------------------------------
$label = 'THE VALUE';            >  |before-NEW VALUE-after|
%block = (label=>'NEW VALUE');
------------------------------------------------------------------------
$label = 'THE VALUE';            >  |before-NEW VALUE-after|
$block = {label=>'NEW VALUE'};
------------------------------------------------------------------------
$label = 'THE VALUE';            >  NEW CONTENT|before-THE VALUE-after|
@block = ('NEW CONTENT',            |before-NEW VALUE-after|
          {},
          {label=>'NEW VALUE'});
------------------------------------------------------------------------
$label = 'THE VALUE';            >  NEW CONTENT|before-THE VALUE-after|
$block = ['NEW CONTENT',            |before-NEW VALUE-after|
          {},
          {label=>'NEW VALUE'}];
------------------------------------------------------------------------
sub label { scalar localtime }   >  |before-Tue Sep 10 14:52:24 2002-
$block = {};                        after|
------------------------------------------------------------------------
$label = 'THE VALUE';            >  |BEFORE-{LABEL}-AFTER|
sub block { uc shift }
------------------------------------------------------------------------

Different combinations of values and zones can easily produce complex ouputs: see the other topics in this section.

Include a file

To include a file in a template just set a label with the pathname of the file as identifier, surrounded by quotes:

{'/temp/footer.html'}

The file will be included in place of the label and if it is a template, it will be processed as usual.

Redefine Markers

by explicitly define the markers constructor parameter

# redefine the markers as needed
$mt = new Text::MagicTemplate
          markers => [qw( <- / -> ) ] ;

by using a standard markers

The standard installation comes with a HTML friendly "standard markers" that implements a HTML-comment-like syntax. If your output is an HTML text - or just because you prefer that particular look - you can use it instead of using the default markers.

$mt = new Text::MagicTemplate
          markers => 'HTML' ;

# that means
$mt = new Text::MagicTemplate
          markers => [ qw( <!-- / --> ) ] ;

See "markers" constructor parameter key for details.

Setup a template

A quick way to setup a template in 4 simple steps is the following:

1 Prepare an output: Prepare a complete output as your code could print. Place all the static items of your output where they should go, place placeholders (any runtime value that your code would supply) where they should go and format everything as you want
2 Choose names: Choose meaningful names (or variables and subroutines names if you already have a code) for labels and blocks
3 Insert single labels: Find the dynamic items in the template and replace them with a label, or if you want to keep them as visible placeholders, transform each one of them into a block
4 Define blocks: If you have any area that will be repeated by a loop or that will be printed just under certain conditions transform it into a block.

Setup placeholders

These are a couple of templates that use a HTML friendly sintax. The output will be the same for both templates, with or without placeholders: the difference is the way you can look at the template.

template without placeholders

<p><hr>
Name: <b style="color:blue"><!--{name}--></b><br>
Surname: <b style="color:blue"><!--{surname}--></b>
<hr></p>

This is what you would see in a WYSIWYG editor: (you should be using a browser to see the example below this line)

Name:
Surname:

template with placeholders

The placeholders "John" and "Smith" are included in blocks and will be replaced by the actual values of 'name' and 'surname' from your code.

<p><hr>
Name: <b style="color:blue"><!--{name}-->John<!--{/name}--></b><br>
Surname: <b style="color:blue"><!--{surname}-->Smith<!--{/surname}--></b>
<hr></p>

This is what you would see in a WYSIWYG editor: (you should be using a browser to see the example below this line)

Name: John
Surname: Smith

Setup simulated areas

If you want to include in your template some area only for design purpose (for example to see, right in the template, how could look a large nested loop), just transform it into a block and give it an identifier that will never be defined in your code.

{my_simulated_area} this block simulates a possible output
and it will never generate any output {/my_simulated_area}

Setup labeled areas

If you want to label some area in your template (for example to extract the area to mix with another template), just transform it into a block and give it an identifier that will always be defined in your code. A convenient way to do so is to set the identifier to a reference to an empty hash. This will generate the output of the block and (since the array does not contain any keys) the lookup will fallback into the stored locations.

the code

$my_labeled_area = {};  # a ref to an empty hash

the template

{my_labeled_area}
this block will always generate an output
{/my_labeled_area}

Build a loop

the template

A loop is represented by a block, usually containing labels:

A loop:
{my_loop}-------------------
Date: {date}
Operation: {operation}
{/my_loop}-------------------

the code

You should have some array of hashes (or a reference to) defined somewhere:

$my_loop = [
              {
                  date      => '8-2-02',
                  operation => 'purchase'
              },
              {
                  date      => '9-3-02',
                  operation => 'payment'
              }
            ] ;

the output

A loop:
-------------------
Date: 8-2-02
Operation: purchase
-------------------
Date: 9-3-02
Operation: payment
-------------------

Build a nested loop

the template

A nested loop is represented by a block nested into another block:

A nested loop:
{my_nested_loop}-------------------
Date: {date}
Operation: {operation}
Details:{details}
           - {quantity} {item}{/details}
{/my_nested_loop}-------------------

Note that the block 'details' is nested into the block 'my_nested_loop'.

the code

You should have some array nested into some other array, defined somewhere:

# a couple of nested "for" loops may produce this:
$my_nested_loop = [
                     {
                        date      => '8-2-02',
                        operation => 'purchase',
                        details   => [
                                        {
                                           quantity => 5,
                                           item     => 'balls'
                                         },
                                         {
                                           quantity => 3,
                                           item     => 'cubes'
                                         },
                                         {
                                           quantity => 6,
                                           item     => 'cones'
                                         }
                                     ]
                     },
                     {
                        date      => '9-3-02',
                        operation => 'payment',
                        details   => [
                                        {
                                           quantity => 2,
                                           item     => 'cones'
                                         },
                                         { quantity => 4,
                                           item     => 'cubes'}
                                     ]
                      }
                  ] ;

Note that the value of the keys 'details' are a reference to an array of hashes.

the output

A nested loop:
-------------------
Date: 8-2-02
Operation: purchase
Details:
          - 5 balls
          - 3 cubes
          - 6 cones
-------------------
Date: 9-3-02
Operation: payment
Details:
          - 2 cones
          - 4 cubes
-------------------

Setup an if-else condition

the template

An if-else condition is represented with 2 blocks

{OK_block}This is the OK block, containig {a_scalar}{/OK_block}
{NO_block}This is the NO block{/NO_block}

the code

Remember that a block will be deleted if the lookup of the identifier returns the UNDEF value, so your code will determine what block will generate output (defined identifier) and what not (undefined identifier).

if ($OK) { $OK_block = {a_scalar => 'A SCALAR VARIABLE'} }
else     { $NO_block = {} }

Same thing here:

$a_scalar = 'A SCALAR VARIABLE';
$OK ? $OK_block={} : $NO_block={};

the output

A true $OK would leave undefined $NO_block, so it would produce this output:

This is the OK block, containig A SCALAR VARIABLE

A false $OK would leave undefined $OK_block, so it would produce this output:

This is the NO block

Note that $OK_block and $NO_block should not return a SCALAR value, that would replace the whole block with the value of the scalar.

Setup a switch condition

the template

A simple switch (if-elsif-elsif) condition is represented with multiple blocks:

{type_A}type A block with {a_scalar_1}{/type_A}
{type_B}type B block with {a_scalar_2}{/type_B}
{type_C}type C block with {a_scalar_1}{/type_C}
{type_D}type D block with {a_scalar_2}{/type_D}

the code

Your code will determine what block will generate output (defined identifier) and what not (undefined identifier). In the following example, value of $type will determine what block will produce output, then the next line will define $type_C using a symbolic reference:

$type  = 'type_C';
$$type = { a_scalar_1 => 'THE SCALAR 1',
           a_scalar_2 => 'THE SCALAR 2' };

Same thing yet but with a different programming style:

$a_scalar_1 = 'THE SCALAR 1';
$a_scalar_2 = 'THE SCALAR 2';
$type       = 'type_D';
$$type      = {};

Same thing without using any symbolic reference:

$type           = 'type_D';
$my_hash{$type} = { a_scalar_1 => 'THE SCALAR 1',
                    a_scalar_2 => 'THE SCALAR 2' };
$mt = new Text::MagicTemplate
          lookups => \%my_hash ;

the output

A $type set to 'type_C' would produce this output:

type C block with THE SCALAR 1

A $type set to 'type_D' would produce this output:

type D block with THE SCALAR 2

Pass parameters to a subroutine

Text::MagicTemplate can execute subroutines from your code: when you use a zone identifier that matches with a subroutine identifier, the subroutine will receive the zone object as a parameters and will be executed. This is very useful when you want to return a modified copy of the template content itself, or if you want to allow the designer to pass parameter to the subroutines.

This example show you how to allow the designer to pass some parameters to a subroutine in your code. The 'matrix' sub, used in the example, receives the parameters written in the template and generates just a table filled of 'X'.

the template

{matrix}5,3{/matrix}

The content of 'matrix' block ('5,3') is used as parameter

the code

sub matrix
{
    my ($zone) = @_;
    my ($column, $row) = split ',' , $zone->content; # split the parameters
    my $out;
    for (0..$row-1) {$out .= 'X' x $column. "\n"};
    $out;
}

The sub 'matrix' receive the reference to the zone object, and return the output for the block

the output

XXXXX
XXXXX
XXXXX

The same example with named parameters, could be written as follow:

the template

{matrix columns => 5, rows => 3}

The attributes string of 'matrix' label (' columns => 5, rows => 3') is used as parameter

the code

sub matrix
{
    my ($zone) = shift;
    my $attributes = $zone->attributes;
    $attributes =~ tr/ //d; # no spaces
    my %attr = split /=>|,/, $attributes; # split the parameters
    my $out;
    for (0..$attr{rows}-1) {$out .= 'X' x $attr{columns} . "\n"};
    $out;
}

The sub 'matrix' receive the reference to the zone object, and return the output for the block

the output

XXXXX
XXXXX
XXXXX

Pass a structure to a subroutine

You can use the '_EVAL_ATTRIBUTES_' zone handler to pass compless named structures to a subroutine.

A simple example that use the '_EVAL_ATTRIBUTES_' zone handler could be:

$mt = new Text::MagicTemplate
          markers       => ['<<', '/', '>>']   , # to avoid conflict
          zone_handlers => '_EVAL_ATTRIBUTES_' ;

This is a possible example of template:

text <<my_sub {color => 'red', quantity => 2}>> text

The '_EVAL_ATTRIBUTES_' zone handler set the param property to the evalued attributes string {color = 'red', quantity => 2}> in the template, so you can use it directly in your sub:

sub my_sub
{
  my ($z) = @_ ;
  'The color is '. $z->param->{color}
  . ' the quantity is '. $z->param->{quantity}
}

WARNING: You should use '_EVAL_ATTRIBUTES_' handler ONLY if you are the programmer AND the designer.

Use subroutines to rewrite links

If you use a block identifier that matches with a subroutine identifier, the subroutine will receive the content of the block as a single parameter and will be executed. This is very useful when you want to return a modified copy of the template content itself.

A typical application of this capability is the template of a HTML table of content that point to several template files. You can use the capabilities of your favourite WYSIWYG editor to easily link each menu in the template with each template file. By doing so you will generate a static and working HTML file, linked with the other static and working HTML template files. This will allow you to easily check the integrity of your links, and preview how the links would work when utilized by your program.

Then a simple modify_link subroutine - defined in your program - will return a self-pointing link that will be put in the output in place of the static link. See the example below:

the template

<p><a href="<!--{modify_link}-->add.html<!--{/modify_link}-->">Add Item
</a></p>
<p>
<a href="<!--{modify_link}-->update.html<!--{/modify_link}-->">Update Item
</a></p>
<p>
<a href="<!--{modify_link}-->delete.html<!--{/modify_link}-->">Delete Item
</a></p>

Working links pointing to static templates files (useful for testing and preview purpose, without passing through the program)

the code

sub modify_link
{
    my ($zone) = shift;
    my ($content) = $zone->content;
    $content =~ m|([^/]*).html$|;
    return '/path/to/myprog.cgi?action='.$content;
}

the output

<p><a href="/path/to/myprog.cgi?action=add">Add Item</a></p>
<p><a href="/path/to/myprog.cgi?action=update">Update Item</a></p>
<p><a href="/path/to/myprog.cgi?action=delete">Delete Item</a></p>

Working links pointing to your program, defining different query strings.

Prepare the identifiers description list

If you have to pass to a webmaster the description of every identifier in your program utilized by any label or block, Text::MagicTemplate can help you by generating a pretty formatted list of all the identifiers (from labels and blocks) present in any output printed by your program. Just follow these steps:

1 Add the following line anywhere before printing the output:

Text::MagicTemplate->ID_list;

2 Capture the outputs of your program

Your program will run exactly the same way, but instead of print the regular outputs, it will print just a pretty formatted list of all the identifiers present in any output.

3 Add the description

Add the description of each label and block to the captured output and give it to the webmaster.

Allow untrustworthy people to edit the template

MagicTemplate.pm does not use any eval() statement, it just do a recursive search and replace with the content of the template. Besides, the allowed characters for identifiers are only alphanumeric (\w+), so even dealing with tainted templates should not raise any security problem that you wouldn't have in your program itself.

However, since the module is just about 300 lines of code, you should consider to analyze it directly. If you do this, please send me some feedback.

Avoid unwanted executions

This module can execute the subroutines of your code whenever it matches a label or block identifier with the subroutine identifier. Though unlikely, it is possible in principle that someone (only if allowed to edit the template) sneaks the correct identifier from your code, therefore, if you have any potentially dangerous subroutine in your code, you should restrict this capability. To do this, you can omit the CODE value handler, or pass only explicit locations to the new() method.

potentially unsafe code

sub my_potentially_dangerous_sub { unlink 'database_file' };
$name = 'John';
$surname = 'Smith';

# automatic lookup in __PACKAGE__ namespace
$mt = new Text::MagicTemplate ;

With this code, a malicious person allowed to edit the template could add the label {my_potentially_dangerous_sub} in the template and that label would trigger the deletion of 'database_file'.

code with subs_execution disabled

Just explicitly omit the CODE value handler when you create the object, so no sub will be executed:

$mt = new Text::MagicTemplate
          value_handler => [ qw( SCALAR REF ARRAY HASH ) ] ;

code with restricted lookups

sub my_potentially_dangerous_sub { unlink 'database_file' };
%my_restricted_hash = ( name => 'John', surname => 'Smith' );

# lookup in %my_restricted_hash only
$mt = new Text::MagicTemplate
          lookups => \%my_restricted_hash ;

With this code the lookup is restricted to just the identifiers used in the template, thus the subroutine my_potentially_dangerous_sub is unavailable to the outside world. (see new() method).

Embed perl into a template

This example represents the maximum degree of inclusion of perl code into a template: in this situation, virtually any code inside the '_EVAL_' block will be executed from the template.

WARNING: For obvious reasons you should use this handler ONLY if you are the programmer AND the designer.

the template

{_EVAL_}$char x ($num+1){/_EVAL_}

The content of '_EVAL_' block could be any perl expression

the code

$mt = new Text::MagicTemplate
          zone_handlers =>  '_EVAL_' ;
$char = 'W';
$num = 5;

the output

The handler will generate as the output the evaluated content of the block.

WWWWWW

Since a block can contain any quantity of text, you could use this type of configuration as a cheap way to embed perl into (HTML) files.

Note that the default syntax markers ({/}) could somehow clash with perl blocks, so if you want to embed perl into your templates, you should consider to redefine the syntax with some more appropriate marker (See "Redefine Markers").

SYNTAX GLOSSARY

attributes string

The attributes string contains every character between the end of the label identifier and the end label marker. This is optionally used to pass special parameters to a sub.

block

A block is a template zone delimited by (and including) a label and an end label:

+-------+-------------------+------------+
| LABEL |      CONTENT      | END_LABEL  |
+-------+-------------------+------------+

Example: {my_identifier} content of the block {/my_identifier}

where '{my_identifier}' is the LABEL, ' content of the block ' is the CONTENT and '{/my_identifier}' is the END_LABEL.

end label

An end label is a string in the form of:

+--------------+---------------+------------+------------+
| START_MARKER | END_MARKER_ID | IDENTIFIER | END_MARKER |
+--------------+---------------+------------+------------+

Example of end label : {/my_identifier}

where '{' is the START_MARKER, '/' is the END_MARKER_ID, 'my_identifier' is the IDENTIFIER, and '}' is the END_MARKER.

identifier

A label identifier is a alphanumeric name (\w+) that represents (and usually matches) a variable or a subroutine identifier of your code.

illegal blocks

Each block in the template can contain arbitrary quantities of nested labels and/or blocks, but it cannot contain itself (a block with its same identifier), or cannot be cross-nested.

Legal block: {block1}...{block2}...{/block2}...{/block1}

Illegal auto-nested block: {block1}...{block1}...{/block1}...{/block1}

Illegal cross-nested block: {block1}...{block2}...{/block1}...{/block2}

If the template contains any illegal block, unpredictable behaviours may occur.

include label

An include label is a label used to include a template file. The identifier must be surrounded by single or double quotes and should be a valid path.

Example: {'/templates/temp_file.html'}

label

A label is a string in the form of:

+--------------+------------+------------+------------+
| START_MARKER | IDENTIFIER | ATTRIBUTES | END_MARKER |
+--------------+------------+------------+------------+

Example: {my_identifier attribute1 attribute2}

where '{' is the START_MARKER, 'my_identifier' is the IDENTIFIER, 'attribute1 attribute2' are the ATTRIBUTES and '}' is the END_MARKER.

lookup

The action to match label identifier with code identifier (variable, subroutine and method identifier and hash keys).

main template zone

The 'root' zone representing the whole template content

markers

The markers that defines a labels and blocks. These are the default values of the markers that define the label:

START_MARKER:   {
END_MARKER_ID:  /
END_MARKER:     }

You can redefine them by using the markers constructor array. (see "Redefine Markers" and markers).

matching identifier

The identifier (symbol name or key name) in the code that is matching with the zone or label identifier

merger process

The process that merges runtime values with a template producing the final output

nested block

A nested block is a block contained in another block:

+----------------------+
|   CONTAINER_BLOCK    |
|  +----------------+  |
|  |  NESTED_BLOCK  |  |
|  +----------------+  |
+----------------------+

Example: {my_container_identifier} {my_nested_identifier} content of the block {/my_nested_identifier} {/my_container_identifier}

where all the above is the CONTAINER_BLOCK and '{my_nested_identifier} content of the block {/my_nested_identifier}' is the NESTED_BLOCK.

output

The output is the result of the merger of runtimes values with a template

template

A template is a text content or a text file (i.e. plain, HTML, XML, etc.) containing some label or block.

value type

The type of the value found by a lookup (i.e. UNDEF, SCALAR, HASH, ARRAY, ...), that is usually used in the value handler condition to trigger the value handler.

zone

A zone is an area in the template that must have an identifier, may have an attributes string and may have a content. A zone without any content is also called label, while a zone with content is also called block.

zone object

A zone object is an internal object representing a zone.

SUPPORT and FEEDBACK

I would like to have just a line of feedback from everybody who tries or actually uses this module. PLEASE, write me any comment, suggestion or request. ;-)

More information at http://perl.4pro.net/?Text::MagicTemplate.

AUTHOR

Domizio Demichelis, <dd@4pro.net>.

COPYRIGHT

Copyright (c)2002 Domizio Demichelis. All Rights Reserved. This is free software; it may be used freely and redistributed for free providing this copyright header remains part of the software. You may not charge for the redistribution of this software. Selling this code without Domizio Demichelis' written permission is expressly forbidden.

This software may not be modified without first notifying the author (this is to enable me to track modifications). In all cases the copyright header should remain fully intact in all modifications.

This code is provided on an "As Is'' basis, without warranty, expressed or implied. The author disclaims all warranties with regard to this software, including all implied warranties of merchantability and fitness, in no event shall the author, be liable for any special, indirect or consequential damages or any damages whatsoever including but not limited to loss of use, data or profits. By using this software you agree to indemnify the author from any liability that might arise from it is use. Should this code prove defective, you assume the cost of any and all necessary repairs, servicing, correction and any other costs arising directly or indrectly from it is use.

The copyright notice must remain fully intact at all times. Use of this software or its output, constitutes acceptance of these terms.

CREDITS

Thanks to Mark Overmeer http://search.cpan.org/author/MARKOV/ that has submitted a variety of code cleanups/speedups and other useful suggestions.

To install Text::MagicTemplate, copy and paste the appropriate command in to your terminal.

cpanm

cpanm Text::MagicTemplate

CPAN shell

perl -MCPAN -e shell
install Text::MagicTemplate

For more information on module installation, please visit the detailed CPAN module installation guide.

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NAME

VERSION 3.03

WARNING!

SYNOPSIS

DESCRIPTION

How it works

Simple example

More complex example

Policy

Features

INSTALLATION

METHODS

new ( [constructor_arrays] )

output ( template [, identifier] )

print ( template [, identifier] )

get_block ( template [, identifier] )

set_block ( template, identifier, new_content )

STATIC METHODS

ID_list ( [identation_string [, end_marker]] )

CUSTOMIZATION

Constructor Arrays

markers

standard markers

lookups

zone_handlers

standard zone handlers

value_handlers

standard value handlers

output_handlers

standard output handlers

text_handlers

post_handlers

HOW TO...

Understand the output generation

Include a file

Redefine Markers

Setup a template

Setup placeholders

Setup simulated areas

Setup labeled areas

Build a loop

Build a nested loop

Setup an if-else condition

Setup a switch condition

Pass parameters to a subroutine

Pass a structure to a subroutine

Use subroutines to rewrite links

Prepare the identifiers description list

Allow untrustworthy people to edit the template

Avoid unwanted executions

Embed perl into a template

SYNTAX GLOSSARY

SEE ALSO

SUPPORT and FEEDBACK

AUTHOR

COPYRIGHT

CREDITS

Module Install Instructions