NAME

Template - Template processing front-end to the Template Toolkit

SYNOPSIS

use Template;

my $template = Template->new(\%config);

my %params = (
    var1  => $value,
    var2  => \%hash,
    var3  => \@list,
    var4  => \&code,
    var5  => $object,
);

$template->process($input, \%params)
    || die $template->error();

TEMPLATE DIRECTIVES

  COMMENT   - [% # this is a comment  %]

  GET       - [% GET variable %]
              [%     variable %]

  SET       - [% SET variable = value %]
              [%     variable = other_variable
                     variable = 'literal text @ $100'
                     variable = "interpolated text: $var"
                     variable = [ val, val, val, val, ... ]
                     variable = { var = val, var = val, ... }
              %]

  DEFAULT   - [% DEFAULT variable = value %]  # params as above...

  INCLUDE   - [% INCLUDE template %]
	      [% INCLUDE template params %]

  FOREACH   - [% FOREACH variable = [ val, val, val ] %]
              [% FOREACH variable = value %]
              [% FOREACH value %]
                 content
              [% END %]

  IF/UNLESS - [% IF condition %]
                 content
	      [% ELSIF condition %]
		 content
	      [% ELSE %]
		 content
              [% END %]

              [% UNLESS condition %]
                 content
              [% # ELSIF/ELSE as per IF, above %]
	         content
              [% END %]

  BLOCK     - [% BLOCK template %]
                 content
	      [% END %]

  USE       - [% USE plugin %]
              [% USE plugin( params ) %] 
              [% USE variable = plugin( params ) %]
          
  CATCH     - [% CATCH errtype %]
                 content
              [% END %]

  THROW     - [% THROW errtype value %]

  ERROR     - [% ERROR value %]
     
  RETURN    - [% RETURN %]

  STOP      - [% STOP %]

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 directives instruct the template processor to perform certain actions and collectively constitute the language that the toolkit implements. Anything not specially marked as a template directive is treated as plain text and gets passed through intact. You can choose what mark-up tags to use but in the default case, directives are embedded [% like this %].

The toolkit is designed to be fast, flexible and easy to use, allowing you to construct entire content systems from a number of small, reusable components. It can be customised, modified and extended to serve in almost any template-based application.

It is ideally suited for generating web content, but it is by no means limited or specific to this or any other application area. Instead, it supports a simple "plugin" interface for dynamically loading extension code to satisfy different requirements. It encourages the clean separation of user interface elements (sub-templates) and code (plugin modules or other Perl objects/code), promoting flexibility, re-use and ease of development and subsequent maintenance.

The 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 strongly encouraged.

FEATURES

-: Fast, flexible, generic and open template processing system.
-: Simple template "micro-language" provides basic functionality to manipulate variables (GET/SET), process other template component files (INCLUDE), iterate through various values (FOREACH) and conditional branching (IF/ELSIF/ELSE).
-: More complex application code can be developed in Perl (or C, C++, etc) and maintained separately. Template processor binds user code to variables to provide access to application functionality from templates.
-: This natural extensibility promotes the separation of the application from the interface. Template documents remain simple and focussed on rendering the interface. Application code can be made more generic by concentrating on what the application does, not what it looks like.
-: Ideally suited, but not limited to, web content generation. Front-end modules and/or scripts provided for use with static pages, CGI scripts, Apache/mod_perl handlers, etc.
-: Template documents parsed by a fast LALR(1) parser which is generated from a YACC-like grammar. Parse::Yapp is used to compile the grammar. Parser grammar can be modified and re-compiled to create custom template languages.
-: Parsed template documents are compiled to an intermediate form and cache. They can subsequently be rendered repeatedly in minimal time.
-: Stash object manages references to complex external code and data and provides a simple template interface via bound variables.
-: Variables may be partitioned into nested namespaces.
-: Custom error handling and recovery mechanisms implemented as basic exception handling. Users can define template blocks to be processed automatically when errors occur and define the subsequent course of action.
-: Iterator objects can be created to handle complex set iteration. This is handled transparently by the FOREACH directive.
-: Provides an extensible framework for other template languages, processors and applications.
-: Template language is independent (theoretically at least) of the implementation language, platform, operating system, etc.
-: Extensive documentation, test suite, examples, etc.
-: Fully open source code. Contributions, collaborations, suggestions and other feedback welcome.
-: Mailing list: send email to majordomo@cre.canon.co.uk containing the text "subscribe templates".

PREREQUISITES

At present, the Template Toolkit requires Perl 5.005. Efforts will soon be made to support some earlier versions (e.g. 5.004).

OBTAINING AND INSTALLING THE TEMPLATE TOOLKIT

The Template Toolkit module bundle is available from CPAN. As the 'perlmod' manual page explains:

CPAN stands for the Comprehensive Perl Archive Network.
This is a globally replicated collection of all known Perl
materials, including hundreds of unbundled modules.  
[...]
For an up-to-date listing of CPAN sites, see
http://www.perl.com/perl/ or ftp://ftp.perl.com/perl/ .

The module is available as:

/authors/id/ABW/Template-Toolkit-<version>.tar.gz

Unpack the archive to create an installation directory. Something like this:

zcat Template-Toolkit-<version>.tar.gz | tar xvf -

'cd' into that directory, make, test and install the modules:

cd Template-Toolkit-<version>
perl Makefile.PL
make
make test
make install

The 't' sub-directory contains a number of test scripts that are run when a 'make test' is run. You may find some of the examples to be enlightening and others perplexing.

The 'make install' will install the module on your system. You may need administrator privileges to perform this task. If you install the module in a local directory (for example, by executing "perl Makefile.PL LIB=~/lib" in the above - see perldoc MakeMaker for full details), you will need to ensure that the PERL5LIB environment variable is set to include the location, or add a line to your scripts explicitly naming the library location:

use lib '/local/path/to/lib';

DESCRIPTION

The Template module is a simple front-end to the Template Toolkit. It implements a generic template processing object which loads and uses other Template Toolkit modules as required to process template documents.

use Template;
my $tproc = Template->new();

Constants defined in Template::Constants can be imported by using the module and specifying import tags. Alternatively, you can simply add them to the 'use Template' line which will delegate to the Template::Constants module.

use Template qw( :status );

The object may be configured by passing a hash reference to the new() constructor.

my $tproc = Template->new({
    INTERPOLATE => 1,
    PRE_CHOMP   => 1,
});

Templates are rendered by calling the process() method on the Template object. The first parameter specifies the template input and may be a filename, a reference to a text string (SCALAR) containing template text or a reference to a GLOB or IO::Handle (or sub-class) from which the template should be read. The process returns 1 if the template was successfully rendered or 0 if an error occureed. In the latter case, the relevant error message can be retrieved by calling the error() method.

$tproc->process($myfile)
    || die $tproc->error(), "\n";

The second optional parameter may be a hash reference which defines variables for use in the template. The entries in this hash may be simple values, references to hashes, lists, sub-routines or objects (described in detail below).

my $data = {
    'name' => 'John Doe'
    'id'   => 'jdoe',
};

$tproc->process($myfile, $data) 
    || die $tproc->error(), "\n";

TEMPLATE SYNTAX AND DIRECTIVES

DIRECTIVE TAGS

The default syntax for embedding directives in template documents is to enclosed them within the character sequences '[%' and '%]'. See the START_TAG, END_TAG and TAG_STYLE options for details on how to change these tokens.

[% INCLUDE header %]

<h1>Hello World!</h1>
<a href="[% page.next %]"><img src="[% icon.next %].gif"></a>

[% INCLUDE footer %]

For backwards compatibility with Text::MetaText, the default TAG_STYLE also allows the '%%' token to be used as both the start and end of tags.

%% INCLUDE header %%    # for backwards compatibility

Directives may be embedded anywhere in a line of text and can be split across several lines. Whitespace is generally ignored within the directive, except where used to separate parameters.

[% INCLUDE header		   
   title  = 'Hello World' 
   bgcol  = '#ffffff' 
%]

[%INCLUDE menu align='right'%]

Name: [% name %]  ([%id%])

Directives that start with a '#' are treated as comments and ignored. No output is generated. This is useful for commenting template documents or temporarily disabling certain directives.

[% # This is a comment and will be ignored %]

CLEANING UP WHITESPACE

Anything outside a directive tag is considered plain text and is generally passed through unaltered (but see INTERPOLATE below). This includes all the whitespace and newlines characters surrounding directive tags. When tags are processed, they may generate no output but leave a 'gap' in the output document.

Example: Foo [% a = 10 %] Bar

Output: Foo

Bar

The PRE_CHOMP and POST_CHOMP options help to reduce this extraneous whitespace. If a directive appears at the start of a line, or on a line with nothing but whitespace in front of it, then a PRE_CHOMP will delete any whitespace and the preceding newline character. This effectively moves the directive up onto the previous line. When a directive appears at the end of a line, or on a line with nothing but whitespace following it, then a POST_CHOMP will delete any whitespace and the following newline. This effectively moves the next line up onto the current line.

    Foo <----------.
                   |
,---(PRE-CHOMP)----'
|
`-- [% a = 10 %] --.
                   |
,---(POST-CHOMP)---'
|
`-> Bar

The '-' or '+' processing flags may be added immediately inside the start/end tags to enable or disable pre/post chomping options on a per-directive basis.

[%  a = b  %]   # default PRE_CHOMP and POST_CHOMP
[%- a = b  %]   # do PRE_CHOMP  (remove start of line if blank)
[%  a = b -%]   # do POST_CHOMP (remove rest of line if blank)
[%+ a = b  %]   # don't PRE_CHOMP  (leave start of line intact)
[%  a = b +%]   # don't POST_CHOMP (leave rest of line intact)

See the PRE_CHOMP and POST_CHOMP configuration options, described below.

VARIABLES

Directives generally comprise a keyword such as INCLUDE, FOREACH, IF, etc., possibly followed by one or more expressions, parameters, etc.

The GET and SET directives are provided to retrieve (print) and update variable values, respectively. For the sake of brevity, the GET and SET keywords can be omitted and a lone variable will be implicitly treated as a GET directive while an assignment, or sequence of assignments will be implicitly treated as a SET directive.

 # explicit
 [% GET foo %]
 [% SET bar=baz %]
 [% SET 
    name  = 'Fred'
    email = 'fred@happy.com'
 %]

 # implicit (preferred)
 [% foo %]
 [% bar=baz %]
 [% name  = 'Fred'
    email = 'fred@happy.com'
 %]

The DEFAULT directive is similar to SET but only updates variables that are currently undefined or have no "true" value (in the Perl sense).

[% DEFAULT
   name = 'John Doe'
   id   = 'jdoe'
%]

The INTERPOLATE option allows you to embed variables directly into text without requiring the '[%' and '%]' tags. Instead, the variable name should be prefixed by a '$'. You can use curly braces to explicitly delimit the variable name when required:

# INTERPOLATE => 1
<a href="$page.next"><img src="${icon.next}.gif"></a>

With INTERPOLATE set on, any other '$' characters in your document should be 'escaped' by prefixing them with a '\':

Cost: \$100

BLOCK DIRECTIVES

The FOREACH, BLOCK and CATCH directives mark the start of a block which may contain text or other directives (including other nested blocks) up to the next (balanced) END directive. The IF, UNLESS, ELSIF and ELSE directives also define blocks and may be grouped together in the usual manner.

Metavars:
[% FOREACH item = [ 'foo' 'bar' 'baz' ] %]
   * Item: [% item %]
[% END %]

[% BLOCK footer %]
   Copyright 1999 [% me %]
   [% INCLUDE company/logo %]
[% END %]

[% CATCH file %]
   <!-- File error: [% e.info %] -->
   [% IF debugging %]
      [% INCLUDE debugtxt  msg = "file: $e.info" %]
   [% END %]
[% END %]

[% IF foo %]
   do this...
[% ELSIF bar %]
   do that...
[% ELSE %]
   do nothing...
[% END %]

The IF, ELSIF and UNLESS directives can be used to process or ignore a block based on some run-time condition. Multiple conditions may be joined with ELSIF and/or ELSE blocks.

The following conditional and boolean operators may be used:

== != < <= > >= ! && || and or not

Conditions may be arbitrarily complex and are evaluated left-to-right with conditional operators having a higher precedence over boolean ones. Parenthesis may be used to explicitly determine evaluation order.

Examples:

# simple example
[% IF age < 10 %]
   Hello [% name %], does your mother know you're 
   using her AOL account?
[% ELSE %]
   Welcome [% name %].
[% END %]

# ridiculously contrived complex example
[% IF (name == 'admin' || uid <= 0) && (mode == 'debug' || debug) %]
   I'm confused.
[% ELSIF more > less %]
   That's more or less correct.
[% END %]

DIRECTIVE SYNTAX AND STRUCTURE

Multiple directives may be included within a single tag by separating them with semi-colons.

[% IF debugging; 
     INCLUDE debugtxt  msg = "file: $e.info;
   END 
%]

The IF, UNLESS and FOREACH block directives may be specified immediately after another directive (except other block directives) in a convenient 'side-effect' notation.

[% INCLUDE userinfo FOREACH user = userlist %]
[% INCLUDE debugtxt msg="file: $e.info" IF debugging %] 
[% "Danger Will Robinson" IF atrisk %]

The directive keyword may be specified in any case but you might find that it helps to adopt the convention of always using UPPER CASE to make them visually distinctive from variables.

[% FOREACH item = biglist %]   # Good.  
[% foreach item = biglist %]   # OK, but not recommended

Variable names may contain any alphanumeric characters or underscores. They may be lower, upper or mixed case although the usual convention is to use lower case. The case is significant however, and 'foo', 'Foo' and 'FOO' are all different variables.

The fact that a keyword may be expressed in any case, precludes you from using any variable that has the same name as a reserved word, irrespective of its case. Reserved words are currently:

GET, SET, DEFAULT, INCLUDE, FOR, FOREACH, IF, UNLESS, ELSE, ELSIF, 
USE, THROW, CATCH, ERROR, RETURN, STOP, BLOCK, END, AND, OR, NOT.

e.g. [% include = 10 %] # error - 'INCLUDE' a reserved word

The CASE option forces all directive keywords to be expressed in UPPER CASE. Any word not in UPPER CASE will be treated as a variable. This then allows you to use lower, or mixed case variable names that match reserved words. The CASE option does not change the case sensitivity for variable names, only reserved words. Variable names are always case sensitive. The 'and', 'or' and 'not' operators are the only exceptions to this rule. They can always be expressed in lower, or indeed any case, irrespective of the CASE option, and as such, preclude the use of a variables by any of those names.

  # CASE => 1
  [% include = 10 %]     # OK - 'include' is a variable, 'INCLUDE' 
			 # is the reserved word.
  [% INCLUDE foobar      
       IF foo and bar    # OK - 'and' can always be lower case
  %]

VARIABLE NAMESPACES (HASHES)

The period character, '.', is used to denote separate "namespaces" for variables. A namespace is simply a variable that contains a reference to a hash array of more variables.

  my $data = {
      'home' => 'http://www.myserver.com/homepage.html',
      'user' => {
	  'name' => 'John Doe',
          'id'   => 'jdoe',
      },
      'page' => {
	  'this' => 'mypage.html',
	  'next' => 'nextpage.html',
	  'prev' => 'prevpage.html',
      },
  };

  $tproc->process($myfile, $data) 
      || die $tproc->error(), "\n";

Example: <a href="[% home %]">Home</a> <a href="[% page.prev %]">Previous Page</a> <a href="[% page.next %]">Next Page</a>

Output: <a href="http://www.myserver.com/homepage.html"</a> <a href="prevpage.html">Previous Page</a> <a href="nextpage.html">Next Page</a>

Any key in a hash which starts with a '_' or '.' character will be considered 'private' and cannot be evaluated or updated from within a template.

When you assign to a variable that contains multiple namespace elements (i.e. it has one or more '.' characters in the name), any hashes required to represent intermediate namespaces will be created automatically. In other words, you don't have to explicitly state that a variable ('product' in the next example) will represent a namespace (i.e. reference a hash), you can just use it as such and it will be created automatically.

 [% product.id    = 'XYZ-2000' 
    product.desc  = 'Bogon Generator'
    product.price = 666 
 %]

 # INTERPOLATE => 0
 The [% product.id %] [% product.desc %] costs $[% product.price %].00

Output: The XYZ-2000 Bogon Generator costs $666.00

If you want to create a new variable namespace (i.e. a hash) en masse, then you can use Perl's familiar '{' ... '}' construct to create a hash and assign it to a variable.

 [% product = {
      id    = 'XYZ-2000' 
      desc  = 'Bogon Generator'
      price = 666 
    }
 %]

 # INTERPOLATE => 1 (note escaping of first '$' and braces to scope var)
 The $product.id $product.desc costs \$${product.price}.00

Output: The XYZ-2000 Bogon Generator costs $666.00

Note that commas are optional between key/value pairs and the '=>' token may be used in place of '=' to make things look more familiar to Perl hackers. You can even prefix variables with '$' if you really want to but it's not necessary.

[% product = {
     id    => 'XYZ-2000',
     desc  => 'Bogon Generator',
     price => 666,
     foo   => $bar,    # OK to use '$', but not necessary
    $baz   => $qux,    # this is also OK if you _really_ like $'s
   }
%]

You can copy all the members of a hash into another hash by assigning to the magical 'IMPORT' variable (note UPPER CASE). This has the effect of "importing" a set of variables into another namespace.

 [% user = {
      name = 'John Doe'
      id   = 'jdoe'
    }
 %]

 [% IMPORT=user %] 
 Name: [% name %]   ID: [% id %]

The IMPORT may be specified against any other namespace, or can be used as a parameter in an INCLUDE directive, for example.

[% myuser.age    = 100
   myuser.IMPORT = user
%]

[% INCLUDE userinfo 
     title  = 'Some User Record'
     IMPORT = myuser
%]

userinfo: Title: [% title %] User: [% name %] ID: [% id %] Age: [% age %]

Output Title: Some User Record User: John Doe ID: jdoe Age: 100

The assignment to the IMPORT variable is something of a temporary hack and will probably be changed in a future release. If if proves necessary, IMPORT may become a first-class directive. See the TODO file for more info.

VARIABLE VALUES

Variables may be assigned the values of other variables, unquoted numbers (digits), literal text ('single quotes') or quoted text ("double quotes"). In the latter case, any variable references within the text will be interpolated when the string is evaluated. Variables should be prefixed by '$', using curly braces to explicitly scope variable name where necessary.

[% foo  = 'Foo'  %]               # literal value 'Foo'
[% bar  =  foo   %]               # value of variable 'foo'
[% cost = '$100' %]               # literal value '$100'
[% item = "$foo: ${price}.00" %]  # value "bar: $100.00"

Multiple variables may be assigned in the same directive and are evaluated in the order specified. Thus, the above could have been written:

[% foo  = 'Foo'
   bar  = foo
   cost = '$100'
   item = "$foo: ${price}.00"
%]

VARIABLE LISTS

A list (actually a reference to an anonymous Perl list) can be created and assigned to a variable by enclosing one or more values in square brackets, just like in Perl. The values in the list may be any of those described above. Commas between elements are optional.

[% userlist = [ 'tom' 'dick' 'harry' ] %]

[% foo    = 'Foo'
   mylist = [ foo, 'Bar', "$foo Baz" ]
%]

The FOREACH directive will iterate through a list created as above, or perhaps provided as a pre-defined variable passed to the process() method.

my $data = {
    'name' => 'John Doe'
    'id'   => 'jdoe',
    'items' => [ 'one', 'two', 'three' ],
};

$tproc->process($myfile, $data) 
    || die $tproc->error(), "\n";

Example:

Things:
[% foo = 'Foo' %]
[% FOREACH thing = [ foo 'Bar' "$foo Baz" ] %]
   * [% thing %]
[% END %]

Items:
[% FOREACH i = items %]
   * [% i %]
[% END %]

Stuff:
[% stuff = [ foo "$foo Bar" ] %]
[% FOREACH s = stuff %]
   * [% s %]
[% END %]

Output:

Things:
  * Foo
  * Bar
  * Foo Baz

Items:
  * one
  * two
  * three

Stuff:
  * Foo
  * Foo Bar

VARIABLES BOUND TO USER CODE

Template variables may also contain references to Perl sub-routines (CODE). When the variable is evaluated, the code is called and the return value used in the variable's place. These "bound" variables can be used just like any other:

my $data = {
    'magic' => \&do_magic,
};

$template->process('myfile', $data)
    || die $template->error();

sub do_magic {
    # ...whatever...
    return 'Abracadabra!';
}

myfile: He chanted the magic spell, "[% magic %]", and disappeared in a puff of smoke.

Output: He chanted the magic spell, "Abracadabra!", and disappeared in a puff of smoke

Any additional parameters specified in parenthesis will also be passed to the code:

    $data = {
	'foo'   => 'Mr. Foo',
	'bar'   => 'Mr. Bar',
	'qux'   => 'Qux',
	'join'  => sub { my $joint = shift; join($joint, @); },
    }

    $template->process('myfile', $data)
	|| die $template->error();

myfile: [% join(' + ', foo, bar, 'Mr. Baz', "Mr. $qux") %]

output: Mr. Foo + Mr. Bar + Mr. Baz + Mr Qux

Parenthesised parameters may be added to any element of a variable, not just those that are bound to code or object methods. At present, parameters will be ignored if the variable isn't "callable" but are supported for future extensions. Think of them as "hints" to that variable, rather than just arguments passed to a function.

%% r = 'Romeo' %%
%% r(100, 99, s, t, v) %%     # still just prints "Romeo"

User code should return a value for the 'variable' to which it is bound. On error, undef can be returned which will trigger an "undef" exception to be automatically raised (see below)

sub do_magic {
    # blah blah blah
    return undef if $something_went_wrong;
    # more stuff..
    return $some_value;
}

An alternative approach which gives more flexibility is for the code to return a second value indicating the status. A status of 0 (STATUS_OK) means everything went OK, regardless of whatever value was returned, defined or not. In this case an undefined value would simply be converted to an empty string ''. In other words, no output or error would be generated.

use Template qw( :status );
my $DEBUG = 0;

sub debug {
    return (undef, STATUS_OK) unless $DEBUG;
    # blah blah blah
    return $some_debug_text;
}

The status code can also be STATUS_STOP (immediate stop) or STATUS_RETURN (stop the current template only and return to the caller or point of INCLUDE). The final option is for the status to be an exception object. This is an instance of the Template::Exception class. The first parameter defines the 'type' of error and may be any string you care to define. The CATCH option and CATCH block directive allow you to define custom handling, or template blocks to be processed when different kinds of exception occur, including any user-defined types such as in this example:

  use Template qw( :status );
  use Template::Exception;

  my $tproc = Template->new();
  $tproc->process('example', { sql => \&silly_query_language })
    || die $tproc->error(), "\n";

  sub silly_query_language {
      # some code...

      # stop!
      return (undef, STATUS_STOP) if $some_fatal_error;

      # some more code...

      # raise a 'database' exception that might be caught and handled
      return (undef, Template::Exception->new('database', $DBI::errstr))
	  if $dbi_error_occurred;

      # even more code still..

      # OK, everything's just fine.  Return data
      return $some_data;
  }

example: [% # define a CATCH block for 'database' errors that # prints the error, adds the page footer and STOPs %] [% CATCH database %]  <hr> <h1>Database Error</h1> An unrecoverable database error has occurred: <ul> [% e.info %] </ul> [% INCLUDE footer %] [% STOP %] [% END %]

[% # we're prepared for the worst... %]
[% sql('EXPLODE my_brain INTO a_thousand_pieces') %]

VARIABLES BOUND TO OBJECTS

A variable may contain an object reference whose methods will be called when expressed in the 'object.method' notation. The object reference will implicitly be passed to the method as the first parameter. Any other parameters specified in parenthesis after the method name will also be passed.

package MyObj;

sub new {
    my $class  = shift;
    bless { }, $class;
}

sub bar {
  my ($self, @params) = @_;
  # do something...
  return $some_value; 
}

package main;

my $tproc = Template->new();
my $obj   = MyObj->new();
$tproc->process('example', { 'foo' => $obj, 'baz' => 'BAZ' } )
  || die $tproc->error(), "\n";

example:

[% foo.bar(baz) %]	# calls $obj->bar('BAZ')

Methods whose names start with an underscore (e.g. '_mymethod') will not be called. Parameter passing and return value expectations are as per code references, above.

VARIABLE EVALUATION

A 'dotted' variable may contain any number of separate elements. Each element may evaluate to one of the above variable types and the processor will then correctly use this value to evaluate the rest of the variable.

For example, consider the following variable reference:

[% myorg.user.abw.name %]

This might equate to the following fundamental steps:

'myorg'  is an object reference
'user'   is a method called on the above object returning a tied 
         hash which acts as an interface to a database
'abw'    is fetched from the above hash, triggering the retrieval 
         of a record from the database.  This is returned as a hash
'name'   is fetched from this hash, representing the value of the 
         'name' field in the record.

You don't need to worry about any of the above steps because they all happen automatically. When writing a template, a variable is just a variable, irrespective of how its value is stored, retrieved or calculated.

Intermediate variables may be used and will behave entirely as expected.

[% userdb = myorg.user %]
[% user   = userdb.abw %]
Name: [% user.name %]  EMail: [% user.email %]

An element of a dotted variable can itself be an interpolated value. The variable should be enclosed within the '${' .., '}' characters. In the following example, we use a 'uid' variable interpolated into a longer variable such as the above to return multiple user records from the database.

[% userdb = myorg.user %]
[% FOREACH uid = [ 'abw' 'sam' 'hans' ] %]
   [% user = userdb.${uid} %]
   Name: [% user.name %]  EMail: [% user.email %]
%]

This could be also have been interpolated into the full variable reference:

[% uid  = 'abw'
   name = myorg.user.${uid}.name
%]

You can also use single and double quoted strings inside an interpolated element:

# contrived example
[% letterw = 'w' 
   name = myorg.user.${"ab$letterw"}.name
%]

SIDE NOTE: In a prototype implementation of a more generic component-based programming language I've been playing with, I extended the above syntax to include lists which were automatically converted into iterators. e.g.

# NOTE: this doesn't work in Template Toolkit (yet!)
[% FOREACH name = myorg.user.['abw' 'sam' 'hans'].name %]
   ...
[% END %]

Roughly equivalent to:

# This *DOES* work...
[% FOREACH uid = [ 'abw' 'sam' 'hans' ] %]
   [% name = myorg.user.${uid}.name %]
   ...
[% END %]

This is quite cool in a sick and twisted kinda way, but can actually be very useful. As a bonus, the implementation is simple and efficient. There's a good chance this feature might make it in some time soon. Contact me if you want more info... (END OF SIDE NOTE)

Any namespace element in a variable may contain parenthesised parameters. If the item contains a code reference or represents an object method then the parameters will be passed to that sub-routine/method when called. Parameters are otherwise ignored, but may be used for future extensibility.

A different implementation of the above example might look like this:

[% myorg.user('abw').name %]

Here, the fictional 'user' method of the 'myorg' object takes a parameter to indicate the required record. Thus, it can directly return a hash reference representing the record which can then be examined for the 'name' member. The method could be written to check for the existence of a parameter and return a general access facility, such as the tied hash in the previous example, if one is not provided. Thus, the same underlying Perl code can easily be used in either manner.

package myorg;

sub user {
    my ($self, $uid) = @_;
    return $self->get_record($uid) if $uid;
    return $self->make_tied_hash_to_records();
}

A sub-routine or method might also return a reference to a list containing other objects or data. The FOREACH directive is used to iterate through such lists.

[% FOREACH user = myorg.userlist %]
   Name: [% user.name %]  EMail: [% user.email %]
[% END %]

For more powerful list iteration, a Template::Iterator object can be defined and/or returned for use in a FOREACH directive. The following pseudo-code example illustrates the principal. Here, the 'userlist' method first determines a list of valid user ID's and then creates an iterator to step through them. On each iteration, the ACTION for the iterator is called, which in this case is a closure to retrieve each record from the database.

  package myorg;

  sub user {
      my ($self, $uid) = @_;
      return $self->query("SELECT * FROM user WHERE (uid='$uid')");
  }

  sub userlist {
      my $self = shift;
      my $user_id_list = $self->query("SELECT id FROM user");
      return Template::Iterator->new($user_id_list, {
	    ORDER  => 'sorted',
	    ACTION => sub { $self->user(shift) },
      });
  }

This process is entirely hidden from the template author. The use of iterators is automatic and nothing needs to change in the template:

[% FOREACH user = myorg.userlist %]
   Name: [% user.name %]  EMail: [% user.email %]
[% END %]

Underlying code, algorithms and heuristics may be as simple or as complex as required to perform the task in hand. However, the specific details of the implementation are hidden away in the "back-end", providing only a simple, clear and consistent interface for use in template documents.

INCLUDING TEMPLATE FILES AND BLOCKS

The INCLUDE directive is used to process and include the output of another template file or block.

[% INCLUDE header %]

The processor will look for files relative to the directories specified in the INCLUDE_PATH. Each file is parsed when first loaded and cached internally in a "compiled" form. The contents of the template, including any directives embedded within it, will then be processed and the output included into the current document. Subsequent INCLUDE directives requesting the same file can then use the cached version to greatly reduce processing time.

The first parameter to the INCLUDE directive is assumed to be the name of a file or defined block (see BLOCK, below). The name may contain alphanumeric characters, underscores, dots or slashes ([\w\/\.]). Names that contain any other characters should be quoted. Double quoted strings may be used to interpolate variable values into the name.

[% INCLUDE misc/menu.atml               %]
[% INCLUDE 'dos98/Program Files/stupid' %]
[% INCLUDE "$lang/menu.atml"            %]

Further parameters can be provided to define local variable values for the template.

[% INCLUDE header
   title = 'Cat in the Hat'
   bgcol = '#aabbcc'
%]

header: [% DEFAULT title='Hello World' bgcol='#ffffff' %] <html> <head><title>[% title %]</title></head> <body bgcolor="[% bgcol %]">

Output: <html> <head><title>Cat in the Hat</title></head> <body bgcolor="#aabbcc">

In addition to any parameters explicitly provided, the INCLUDE'd template will "inherit" all other variables currently defined. These variables are 'localised' meaning that any changes made to variable within the included file will not affect those variables in the namespace of the enclosing template.

[% name = 'foo' %] 
[% INCLUDE change_name %]
Name is still '[% name %]'

change_name: Name is [% name %] Changing '[% name %]' to [% name ='bar'; name %]

Output: Name is 'foo' Changing 'foo' to 'bar' Name is still 'foo'

In addition to separate files, template blocks can be defined and processed with the INCLUDE directive. These are defined with the BLOCK directive and are parsed, compiled and cached as for files.

[% BLOCK tabrow %]
<tr><td>[% name %]<td><td>[% email %]</td></tr>
[% END %]

<table>
[% INCLUDE tabrow  name='Fred'  email='fred@nowhere.com' %]
[% INCLUDE tabrow  name='Alan'  email='alan@nowhere.com' %]
</table>

A BLOCK definition may be used before it is defined, as long as the definition resides in he same file.

[% INCLUDE tmpblk %]

[% BLOCK tmpblk %] This is OK [% END %]

PLUGIN OBJECTS AND LIBRARIES

The USE directive can be used to load and initialise "plugin" extension modules. These are regular Perl modules that may, or may not, be derived from the Template::Plugin base class.

[% USE myplugin %]

The plugin name is case-sensitive and will be appended to the PLUGIN_BASE value (default: 'Template::Plugin') to construct a full module name. Any periods, '.', in the name will be converted to '::'.

[% USE MyPlugin   %]     #  => Template::Plugin::MyPlugin
[% USE CGI.Params %]     #  => Template::Plugin::CGI::Params

Any additional parameters supplied in parenthesis after the plugin name will be also be passed to the new() constructor. A reference to the template Context object is always passed as the first parameter.

[% USE MyPlugin('foo', 123) %]
   ==> Template::Plugin::MyPlugin->new($context, 'foo', 123);

The plugin may represent any data type; a simple variable, hash, list or code reference, but in the general case it will be an object reference. Methods can be called on the object (or the relevant members of the specific data type) in the usual way:

[% USE MyPlugin %]
[% MyPlugin.does_this %]
[% MyPlugin.does_that %]

An alternative name may be provided for the plugin by which it can be referenced:

[% USE magic = MyPlugin %]
[% magic.supernova('Big Bang') %]

You can use this approach to create multiple plugin objects with different configurations. This example shows how the 'format' plugin is used to create sub-routines bound to variables for formatting text as per printf().

[% USE bold = format('<b>%s</b>') %]
[% USE ital = format('<i>%s</i>') %]

[% bold('This is bold')   %]
[% ital('This is italic') %]

Output: <b>This is bold</b> <i>This is italic</i>

See Template::Plugin for details of the plugin modules available for the Template::Toolkit.

ERROR HANDLING AND FLOW CONTROL

There are two kinds of error that may occur within the Template Toolkit. The first (which we try to avoid) are 'Perl errors' caused by incorrect usage, or heaven forbid, bugs in the Template Toolkit. See the BUGS section or the TODO file for more detail on those. Thankfully, these are comparatively rare and most problems are simply due to calling a method incorrectly or passing the wrong parameters.

The Template Toolkit doesn't go out of it's way to check every parameter you pass it. On the whole, it is fairly tolerant and will leave it up to Perl's far superior error checking to report anything seriously untoward that occurs.

The other kind of errors that concerns us more are those relating to the template processing "runtime". These are the (un)expected things that happen when a template is being processed that we might be interested in finding out about. They don't mean that the Template Toolkit has failed to do what was asked of it, but rather that what was asked of it didn't make sense, or didn't work as it should. These kind of errors might include a variable being used that isn't defined ('undef'), a file that couldn't be found, or properly parsed for an INCLUDE directive ('file'), a database query that failed in some user code, a calculation that contains an illegal value, an invalid value for some verified data, and so on (any error types can be user-defined).

These kinds of errors are raised as 'exceptions'. An exception has a 'type' which is a single word describing the kind of error, and an 'info' field containing any additional information.

These exceptions may be caught (i.e. "handled") by an entry defined in the hash array passed as the CATCH parameter to the Template constructor. The keys in the hash represent the error types and the values should contain a status code (e.g. STATUS_OK, STATUS_STOP) or a code reference which will be called when exceptions of that type are thrown. Such code references are passed three parameters; a reference to the template "Context" object, the error type and the error info. Having performed any processing, it should then return a status code or an exception object to be propagated back to the user. Returning a value of 0 (STATUS_OK) indicates that the exception has been successfully handled and processing should continue as before.

  my $tproc = Template->new({	
      CATCH => {
	'file'  => sub {
		      my ($context, $type, $info) = @_;
		      $context->output("<!-- $type: ($info) -->");
		      return STATUS_OK;
	           },
	'undef' => STATUS_OK,
      },
  });

A template block may also be defined that will be processed when certain exception types are raised. The CATCH directive starts the block definition and should contain a single word denoting the error type. The variable 'e' will be defined in a catch block representing the error. The 'type' and 'info' members represent the appropriate values.

[% CATCH file %]
  <!-- file error: [% e.info %] -->
[% END %]

A CATCH block defined without an error type will become a default handler. This will be processed when an exception is raised that has no specific handler of its own defined.

[% CATCH %]
  An error ([% e.type %]) occured: 
    [% e.info %]
[% END %]

A default handler can be installed via the CATCH option by defining the error type as 'default'.

  my $tproc = Template->new({	
      CATCH => {
	  'default' => STATUS_OK,
      },
  });

Any user-defined exception types can be created, returned, thrown and caught at will. User code may return an exception as the status code to indicate an error. This exception type can then be caught in the usual way.

$tproc->process('myexample', { 'go_mad' => \&go_mad })
  || die $tproc->error();

sub go_mad {
    return (undef, Template::Exception->new('mad', 'Big Fat Error'));
}

Example: [% CATCH mad %] Gone mad: [% e.info %] [% END %]

Going insane...
[% go_mad %]

Output: Going insane... Gone mad: Big Fat Error

A CATCH block will be installed at the point in the template at which it is defined and remains available thereafter for the lifetime of the template processor or until redefined. This is probably a bug and may soon be 'fixed' so that handlers defined in templates only persist until the parent process() method ends.

An exception that is not caught, or one that is caught by a handler that then propagates the exception onward, will cause the Template process() method to stop and return a false status (failed). A string representing the exception that occured (in the format "$type: $info") can be returned by calling the error() method.

$tproc->process('myexample')
    || die "PROCESSING ERROR: ", $tproc->error(), "\n";

You can 'throw' an exception using the THROW directive, specifying the error type (unquoted) and value to represent the information.

[% THROW mad '19th Nervous Breakdown' %]

Output: PROCESSING ERROR: mad: 19th Nervous Breakdown

The STOP directive can be used to indicate that the processor should stop gracefully without processing any more of the template document. This is known as a 'planned stop' and the Template process() method will return a true value. This indicates 'the template was processed successfully according to the directives within it' which hopefully, it was. If you need to find out if the template ended 'naturally' or via a STOP (or RETURN, as discussed below) directive, you can call the Template error() method which will return the numerical value returned from the last directive, represented by the constants STATUS_OK, STATUS_STOP, STATUS_RETURN, etc. If the previous process() did not return a true value then the error() method returns a string representing the exception that occured.

The STOP directive can be used in conjunction with CATCH blocks to safely trap and report any fatal errors and then end the template process gracefully.

[% CATCH fatal_db_error %]
   <p>
   <b>A fatal database error has occured</b>
   <br>
   Error: [% e.info %]
   <br>
   We apologise for the inconvenience.  The cleaning lady has removed 
   the power from the database server so that she can plug in her
   vacuum cleaner.  She's normally done in about 5 minutes... please
   try again later.
   </p>
   [% ERROR "[$e.type] $e.info" %]
   [% INCLUDE footer %]
   [% STOP %]
[% END %]

The ERROR directive as used in the above example, sends the specified value to the current output stream for the template processor. By default, this is STDERR.

The RETURN directive is similar to STOP except that it terminates the current template file only. If the file in which the RETURN directive exists has been INCLUDE'd by another, then processing will continue at the point immediately after the INCLUDE directive.

Before
[% INCLUDE half_wit %]
After

[% BLOCK half_wit %]
This is just half...
[% RETURN %]
...a complete block
[% END %]

Output: Before This is just half... After

The STOP, RETURN, THROW and ERROR directives can all be used in conjunction with other 'side-effect' directives. e.g.

[% THROW up 'Contents of stomach' IF drunk %]
[% STOP IF brain_exploded %]
[% RETURN IF no_input %]
[% ERROR 'Stupid, stupid, user' IF easy2guess(passwd) %]
[% THROW badpasswd "$user.id has a dumb password ($user.passwd)"
     FOREACH user = naughty_user_list
%]

PUBLIC METHODS

new(\%config)

The new() constructor is called to create and return a new instance of the Template class. This object acts as a front-end processor to the other Template Toolkit modules.

A reference to a hash array may be passed which contains configuration parameters. These may include:

INCLUDE_PATH

The INCLUDE_PATH option specifies one or directories in which to look for template files. Multiple directories can be delimited by a ':' (or the value of the PATH_SEPARATOR) or specified as a reference to a list. Each item in a list may have additional CACHE parameters associated with it.

my $cache = Template::Cache->new({
    INCLUDE_PATH => '/usr/local/templates:/usr/web/templates',
});

my $cache = Template::Cache->new({
    INCLUDE_PATH => [ '/tmp/templates', '/usr/web/templates' ],
});

my $template = Template->new({
    INCLUDE_PATH => [ 
      '/user/web/templates/src:/usr/web/tmplates/elements'
      '/user/web/templates/toodamnbig' => { CACHE => 0 },
    ],
});

The PATH_SEPARATOR and DIR_SEPARATOR options can be used to adjust for different operating system conventions. See Template::Cache for further details.

# accommodate some inferior file-system...
# note the need to escape all those backslashes
my $template = Template->new({ 
    INCLUDE_PATH   => 'D:\\ABW\\TEMPLATES + C:\\TMP',
    PATH_SEPARATOR => ' + ',
    DIR_SEPARATOR  => '\\',
});

PRE_DEFINE

A reference to a hash of variables and values that should be pre-defined in the stash. Passed to Template::Stash new() constructor. These variables will be pre-defined each time process() is called.

  my $template = Template->new({
      PRE_DEFINE => {
	  'server'    => 'www.myorg.com',
	  'help'      => 'help/helpndx.html',
	  'images'    => '/images'
	  'copyright' => '(C) Copyright 1999',
	  'userlist'  => [ 'tom', 'dick', 'harry'   ],
	  'myorg'     => { 'name' => 'My Org. Inc.', 
                           'tel'  => '555-1234'     },
          'icon'      => { 'prev' => 'prevbutton', 
                           'next' => 'nextbutton'   },
      }
  });

START_TAG, END_TAG, TAG_STYLE

The START_TAG and END_TAG options are used to specify character sequences or regular expressions that mark the start and end of a template directive. Any Perl regex characters can be used and therefore should be escaped (or use the Perl quotemeta function) if they are intended to represent literal characters.

my $template->new({ 
    START_TAG => quotemeta('<+'),
    END_TAG   => quotemeta('+>'),
});

example:

<+ INCLUDE foobar +>

The TAG_STYLE option can be used to set both according to pre-defined tag styles. Available styles are:

regular   [% ... %]                (recommended)
percent   %% ... %%                (Text::MetaText compatibility)
default   [% ... %] or %% ... %%   (both of the above)

The default style (TAG_STYLE => 'default') allows either of the 'regular' or 'percent' tags to be used (START_TAG = '[\[%]%', END_TAG = '%[\]%]') Any values specified for START_TAG and/or END_TAG will over-ride those defined by a TAG_STYLE.

INTERPOLATE

The INTERPOLATE flag, when set to any true value will cause variable references in plain text (i.e. not surrounded by START_TAG and END_TAG) to be recognised and interpolated accordingly. Variables should be prefixed by a '$' to identify them. Curly braces can be used in the familiar Perl/shell style to explicitly scope the variable name where required.

# INTERPOLATE = 0
<a href="http://[% server %]/[% help %]">
<img src="[% images %]/help.gif"></a>
[% myorg.name %]


# INTERPOLATE = 1
<a href="http://$server/$help">
<img src="$images/help.gif"></a>
$myorg.name

# explicit scoping with {  }
<img src="$images/${icon.next}.gif">

PRE_CHOMP, POST_CHOMP

These values set the chomping options for the parser. With POST_CHOMP set true, any whitespace after a directive up to and including the newline will be deleted. This has the effect of joining a line that ends with a directive onto the start of the next line.

With PRE_CHOMP set true, the newline and whitespace preceding a directive at the start of a line will be deleted. This has the effect of concatenating a line that starts with a directive onto the end of the previous line.

PRE_CHOMP and POST_CHOMP can be activated for individual directives by placing a '-' at the start and/or end of the directive:

[% FOREACH user = userlist %]
   [%- user -%]
%% END %%

The '-' characters activate both PRE_CHOMP and POST_CHOMP for the one directive '[%- name -%]'. Thus, the template will be processed as if written:

[% FOREACH user = userlist %][% user %][% END %]

Similarly, '+' characters can be used to disable PRE- or POST-CHOMP (i.e. leave the whitespace/newline intact) options on a per-directive basis.

[% FOREACH user = userlist %]
User: [% user +%]
[% END %]

With POST_CHOMP set on, the above example would be parsed as if written:

[% FOREACH user = userlist %]User: [% user %]
[% END %]

CASE

The Template Toolkit treats all variables with case sensitivity. Thus, the variable 'foo' is different from 'Foo' and 'FOO'. Reserved words, by default, may be specified in either case, but are usually UPPER CASE by convention.

[% INCLUDE foobar %]
[% include foobar %]

One side-effect of this is that you cannot use a variable of the same name as a reserved word such as 'include', 'error', 'foreach', etc.

Setting the CASE option to any true value will cause the parser to only consider UPPER CASE words as reserved words. Thus, 'ERROR' remains a reserved word, but 'error', 'Error', 'ERRoR', etc., may all be used as variables.

The only exception to this rule are the 'and', 'or' and 'not' operators which can always be expressed in lower, or indeed any case.

PLUGIN_BASE

This option allows you to define a base package for plugin objects loaded and used via the USE directive. The default base is 'Template::Plugin'. Periods in a plugin name are converted to '::' and the name is appended to the PLUGIN_BASE. Thus the following directive:

%% USE Foobar.Baz %%

Would request and instantiate and object from the plugin module 'Template::Plugin::Foobar::Baz'.

This option currently only allows one directory to be defined. This is an unnecessary restriction which will soon be rectified.

PLUGINS

The PLUGINS option may be specified as a reference to a hash pre-defining plugin objects for the USE directive. Each key in the hash represents a plugin name and the corresponding value, a package name or object which should be used to construct new instances of the plugin object.

  use MyOrg::Template::Plugin::Womble;
  use Template::Plugin::DBI;         # available soon...

  my $dbi_factory = Template::Plugin::DBI->new();

  my $template->new({ 
      PLUGINS => {
	'womble' => 'MyOrg::Template::Plugin::Womble',
	'dbi'    =>  $dbi_factory,
      END_TAG   => quotemeta('+>'),
  });

The new() method is called against the PLUGINS value when a plugin is USE'd. Thus, an entry that specifies a package name will caused instances of that plugin to be created as follows:

[% USE womble %] 
   ==> MyOrg::Template::Plugin::Womble->new($context);

A reference to the Template::Context object in which the plugin will run is passed as the first parameter. The plugin object may store this reference and subsequently use it to control the template process via it's public interface. This gives plugin objects access to the full functionality of the Template Toolkit.

Any parameters specified in parenthesis after the plugin name will be passed to the new() constructor.

[% USE womble('Tomsk') %] 
   ==> MyOrg::Template::Plugin::Womble->new($context, 'Tomsk');

The PLUGINS value may contain an object reference. In identical fashion to the above, the new() method is called against the object, allowing it to act as a constructor object or 'prototype' for other instances of the same, or other objects.

[% USE dbi('dbase_xyz') %]
  ==> $dbi_factory->new($context, 'dbase_xyz');

This approach facilitates the easy implementation and use of plugins that act as singletons (one instance only) or share some state information, such as cached database handles in the DBI example shown here.

Simon Matthews <sam@knowledgepool.com> is currently working on the DBI plugin for the Template Toolkit.

When a plugin is requested via the USE directive that is not specified in the PLUGINS hash, the dynamic loading procedure described under PLUGIN_BASE above will be used. If a module is successfully loaded, the load() sub-routine in that package is called and should return the package name itself (i.e. simply return the first parameter) or an object reference which is then stored and used in the PLUGINS hash as described above.

OUTPUT, ERROR

The OUTPUT and ERROR options may be specified to redirect template output and/or error messages. The value for these options should be a file GLOB or IO::Handle to which the output/error is directed, a CODE reference which is called to handle messages, or a reference to a text string (SCALAR) to which output or error messages are appended.

my $output = '';

my $template = Template->new({
    OUTPUT = \$output,
    ERROR  = sub { print STDERR "Most Bogus Error: ", @_ }
};

The redirect() method can be subsequently called to define new output or error options.

CATCH

The CATCH option may be used to specify a hash array of error handlers which are used when a run time error condition occurs. Each key in the hash represents an error type. The Template Toolkit generates the following error types which have corresponding ERROR_XXX constants.

undef    - an variable was undefined or evaluated undef
file     - file find/open/parse error

User code may generate further errors of any types and custom handlers may be provided to trap them. A handler, defined as the related value in the CATCH configuration hash may be one of the STATUS_XXXX constants defined in Template::Constants (e.g. STATUS_OK, STATUS_STOP) or a code reference which is called when an error occurs. The handler is passed a reference to the context ($self) and the error type and info. The return value should be one of the aforementioned constants or a Template::Exception object.

    use Template qw( :error );

    my $template = Template->new({
	CATCH => {
	    ERROR_UNDEF => STATUS_OK,
	    ERROR_FILE  => sub { 
		my ($context, $type, $info) = @_;
		$context->output("FILE ERROR: $info");
		return STATUS_OK; 
	    },
	}
    });

A 'default' handler may be provided to catch any exceptions not explicitly caught by their own handler. This is equivalent to defining a CATCH block without specifying an error type:

[% CATCH %]
Caught '[% e.type %]' exception:
  [% e.info %]
[% END %]

PARSER, GRAMMAR

The PARSER and GRAMMAR configuration items can be used to specify an alternate parser or grammar for the parser. Otherwise an instance of the default Template::Parser/Template::Grammar will be created and used as required.

See the parser sub-directory of the Template Toolkit distribution for further information on compiling and using your own grammars (some parser expertise required).

use Template;
use MyTemplate::MyGrammar;

my $template = Template->new({ 
   	GRAMMAR = MyTemplate::MyGrammar->new();
});

CACHE

The CACHE item can be used to specify an alternate cache object to handle loading, compiling and caching of template documents. A default Template::Cache object is created otherwise. See Template::Cache for further information.

process($template, \%vars, ...)

The process() method is called to process a template. The first parameter, $template, indicates the template and may be a simple SCALAR containing a filename (relative to INCLUDE_PATH), a reference to a SCALAR which contains the template text or a reference to a GLOB (e.g. \*MYFILE) or IO::Handle or sub-class from which the template is read.

$file = 'hworld.html'
$text = "[% INCLUDE header %]\nHello world!\n[% INCLUDE footer %]"

$template->process($file)
    || die $template->error(), "\n";

$template->process(\$text)
    || die $template->error(), "\n";

$template->process(\*DATA)
    || die $template->error(), "\n";

__END__
[% INCLUDE header %]    
Hello World!
[% INCLUDE footer %]

The optional second parameter may be a reference to a hash array containing variables and values which should be available in the template. These are applied in addition to (and may temporarily modify previous values for) the PRE_DEFINE variables.

Any output generated by processing the template will be sent to the current output stream which is STDOUT by default. Errors are similarly directed to the error stream or STDERR.

The method returns 1 if the template was successfully processed. This includes templates that were ended by a STOP or RETURN directive If an uncaught error occurs, the method returns 0. A relevant error message can then be returned by calling the error() method.

redirect($what, $where)

The redirect() method can be called to redirect the output or error stream for the template processing system. This method simply delegates to the underlying Template::Context object().

The first parameter should specify 'output' or 'error' (defined as the constants TEMPLATE_OUTPUT and TEMPLATE_ERROR in Template::Constants).

The second parameter should contain a file handle (GLOB or IO::handle) to which the output or error stream should be written. Alternatively, $where may be a reference to a scalar variable to which output is appended or a code reference which is called to handle output.

use Template::Context;
use Template::Constants qw( :template );

my $context = Template::Context->new();
my $output  = '';
$context->redirect(TEMPLATE_OUTPUT, \$output);
$context->redirect(TEMPLATE_ERROR, \*STDOUT);

error()

The error() method returns any error message generated by the previous call to the process() method.

If no error occurred, the method returns a numerical value representing the return code of the last directive processed. This will generally be STATUS_OK (0), STATUS_STOP or STATUS_RETURN. Constants representing the values are defined in Template::Constants.

DISTRIBUTION FILES AND DIRECTORIES

The following directories and files comprise the Template Toolkit distribution. See the individual README files in each directory for further information on their contents.

bin/        Template processing scripts; tpage
examples/   Example templates and scripts
lib/        Template Toolkit modules
parser/     Grammar and compiler scripts for parser
t/          Test scripts (run via 'make test')
MANIFEST    Manifest file (ExtUtils::MakeMaker)
Makefile.PL Makefile construction script (ExtUtils::MakeMaker)
Changes     History of visible changes between versions.
TODO        List of bugs, enhancements, planned features, ideas, etc.
README      README file containing general info

BUGS

See the separate TODO file for details of known bugs, limitations and planned features. The Changes file details visible changes in the toolkit between public versions. The definition of 'visible' is of course entirely dependent on how hard you're looking.

If you do find something that looks or acts like a bug, then please report it along with a short example of what doesn't work as advertised and as much relevant detail as you can give about how it manifested itself. The best way to report a bug is to send a short test file that illustrates the problem. You can use t/skel.t as a skeleton test file.

For example: use lib qw( . ./t ../lib ); use Template; require 'texpect.pl';

test_expect(\*DATA);

__DATA__
-- test --
[% a = 10 %]
[% explode(a) %]
-- expect --
Big Bang!

If you are able to find and fix the bug, and feel inclined to do so, then patches are most welcome of all, especially when prepared by diff -u.

The Template Toolkit is an Open Source project and you are encouraged to contribute ideas, suggestions and code. The templates mailing list is currently the focal point for discussion on these matters. Alternatively, you can email the author directly.

To join the mailing list, send email to <majordomo@cre.canon.co.uk> containing the text "subscribe templates".

To email the author directly, send email to <abw@cre.canon.co.uk>. If you don't know how to do that then I'm afraid I can't help you any more.

This is the end of the document and I'm getting tired... Roll the credits.

AUTHOR

Andy Wardley <abw@cre.canon.co.uk>

http://www.kfs.org/~abw/
http://www.cre.canon.co.uk/perl

VERSION

This is version 0.23 of the Template Toolkit.

It is a stable beta release version preceding the imminent release of version 1.0.

Please consult the Changes file for information about visible changes in the Template Toolkit between releases. The TODO file contains details of known bugs, planned enhancements, features, fixes, etc.

COPYRIGHT

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

ACKNOWLEDGEMENTS

The Template Toolkit was derived in part from ideas and techniques developed in the Text::MetaText module. This itself was the public manifestation of an earlier template processing system I developed while working at Peritas Ltd. (now reverted in name to "ICL Training").

The Template Toolkit was developed more recently at Canon Research Centre Europe Ltd. as part of an ongoing research theme into Web-related publishing and content generation. Other tools are in development to compliment the Template Toolkit.

Many people have contributed ideas, inspiration, bug reports and fixes to Text::MetaText and the Template Toolkit, but none more so than Simon Matthews <sam@knowledegpool.com>. He deserves special mention (and wins many beer tokens) for his continued effort and interest over a number of years.

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