++ed by:
CHISEL FRACTAL ECARROLL OALDERS LEEJO

57 PAUSE user(s)
37 non-PAUSE user(s).

Andy Wardley

NAME

Template Toolkit - a Perl toolkit for template processing.

SYNOPSIS

  use Template;

  # some useful options (see docs below for full list)
  my %config = (
      INCLUDE_PATH => '/search/path',  # or list ref
      INTERPOLATE  => 1,               # expand "$var" in plain text
      POST_CHOMP   => 1,               # cleanup whitespace 
      PRE_PROCESS  => 'header',        # prefix each template
      EVAL_PERL    => 1,               # evaluate Perl code blocks
  );

  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

  GET       - evaluate and print a variable or value
              [%  GET variable %]
              [%      variable %]
              [%      hash.var %]
              [% "value: $var" %]

  CALL      - as above without printing result
              [%  CALL variable %]

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

  DEFAULT   - as SET above, if variable(s) not set
              [% DEFAULT variable = value %]

  INCLUDE   - include another template file/block, localising vars
              [% INCLUDE template %]
              [% INCLUDE template  var = val, ... %]

  PROCESS   - as above, without localising variables
              [% PROCESS template %]
              [% PROCESS template  var = val, ... %]

  FOREACH   - repeat block for each value in a list
              [% FOREACH variable = [ val, val, val ] %]
              [% FOREACH variable = list %]
              [% FOREACH list %]
                 content...
                 [% variable %]
              [% END %]

  WHILE     - iterate while condition is true
              [% WHILE condition %]
                 content
              [% END %]

  IF/UNLESS - process block if condition is true/false.
              [% IF condition %]
                 content
              [% ELSIF condition %]
                 content
              [% ELSE %]
                 content
              [% END %]

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

  BLOCK     - define a template block for INCLUDE or PROCESS
              [% BLOCK template %]
                 content
              [% END %]

  MACRO     - create a named macro for some other directive or block
              [% MACRO directive %]

  FILTER    - post-process block through a filter
              [% FILTER name %]
              [% FILTER name( params ) %]
              [% FILTER alias = name( params ) %]
                 content
              [% END %]

  USE       - load a "plugin" module (or any regular Perl module 
              with LOAD_PERL option)
              [% USE name %]
              [% USE name( params ) %] 
              [% USE var = name( params ) %]
              ...
              [% name.method %]
              [% var.method %]

  PERL      - evaluate block of Perl code (requires EVAL_PERL option)
              [% PERL %]
                 # perl code goes here
              [% END %]
              
  CATCH     - define block to catch an exception
              [% CATCH etype %]
                 content...
                 [% e.type %]  [% e.info %]
              [% END %]

  THROW     - throw an exception
              [% THROW etype info %]

  ERROR     - generate an error message (default: to STDERR)
              [% ERROR info %]

  BREAK     - break out of FOREACH/WHILE
              [% BREAK %]
     
  RETURN    - stop processing current template
              [% RETURN %]

  STOP      - stop processing all templates and return to caller
              [% STOP %]

  COMMENT   - ignored and deleted
              [% # this is a comment  %]

  TAGS      - define new tag characters (default: [% %])
              [% TAGS <!-- --> %]

TOOLKIT CONTENTS

The Template Toolkit comprises of a number of Perl modules, scripts and accompanying documentation.

The Template module acts as a general interface to the toolkit and contains comprehensive documentation describing the toolkit, its usage and further sources of reference.

    perldoc Template

The Template::Tutorial document provides an introduction to the Template Toolkit and shows some typical examples of usage.

    perldoc Template::Tutorial

The tpage and ttree scripts are useful utilities for processing template documents, or entire content trees, respectively.

    perldoc tpage
    perldoc ttree

OVERVIEW

The Template Toolkit is a collection of Perl modules which collectively implement a fast, powerful and generic template processing system. In this context, a template is a text document which contains embedded processing "directives". These instruct the template processor to perform certain actions such as; inserting the value of a variable; processing and including another template file or user-defined block; testing some condition and generating output of one kind or another accordingly; iterating through a set of values; and so on. Anything not marked as a template directive is treated as plain text and gets passed through unaltered. By default, directives look something like this:

   [% INCLUDE header %]

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

This gives you the facility to add any programmable functionality you require but without having to write the code directly into the document. In other words, it promotes the separation of application code (the implementation) from the user interface (the presentation). It tries to keep templates clutter-free, concentrating on what the document looks like, and hides away the implementation specific details of how the various items of content are stored, retrieved or calculated.

Development and subsequent maintenance become easier and less error prone when the "back-end" is separated from the "front-end". You (or your web designer) can first decide how the page(s) should look by creating the output templates, perhaps by re-using other common elements that you've already defined for your web site such as headers, footers, menus, etc. Then, you (or your progammer) can create any Perl code required to required to generate the dynamic parts of the content, perhaps by using CPAN modules, one of the existing Template Toolkit "plugins" or by re-using some code you've previously written for another web application running on your site.

The important thing is that the code is developed separately from the template documents. This is a key feature of the Template Toolkit with the emphasis being on moving code out of documents, rather than moving it in. It doesn't matter if you put every function in a separate file or every bit of application code into one big module - just tell the Template Toolkit where to find the code and leave it to handle the rest. The new functionality is then available without distraction or discourse in any and all of your template documents.

This isn't the only way to do it. There are times when the "best solution" in terms of getting the job done quickly and efficiently is to simply embed Perl code directly into the document. The Template Toolkit has an option (EVAL_PERL - disabled by default) to allow Perl code to be embedded into special 'PERL' sections which are then evaluated when the template is processed. These Perl code fragments have full access to the Template Toolkit interface and may read or update variables, process other template files, load plugins, and so on.

If you prefer the embedded Perl approach and have a need to get some functionality into a document with the minimum fuss, setup time and effort, then you might want to consider using a dedicated embedded Perl processor. In those cases, Mark-Jason Dominus' Text::Template module, available from CPAN, comes highly recommended.

In many ways, this is like CGI scripting in reverse. Instead of embedding HTML within the Perl script, you are embeddding Perl within the HTML document. The Template Toolkit tries to better separate the two in attempt to create a more structured approach to constructing dynamic content. There's a slight startup cost to using this approach because, like life in general, it often takes a little longer to get yourself properly organised. The payoff comes in terms of scalability and subsequent ease of re-use - the more you add, the more you benefit from having structure. That's not to say that you can't use it in many interesting ways with just a single document, but if you only have a single document to worry about then the chances are that you haven't got a lot to worry about.

So rather than emphasing the raw programming power embeddable within any single document, it focuses on tools and techniques to help better partition and subsequently re-integrate the different components that constitute the many documents in a system. It offers speed and simplicity in constructing document systems and delegates "real programming" to a more powerful, general purpose language - Perl.

There are many benefits to be gained from keeping Perl code separate from template documents. You could, for example, write a single web application with a dozen different sets of templates to represent alternate user interfaces. These would represent multiple "views" on the same underlying "model" and might differ in layout or design style, contain text only or go hard on the graphics, contain HTML frames or not, show "novice" or "expert" functionality, allow per-user customisation, present an internationalised or localised interface, and so on. On the other side of the same coin, you could change your underlying code to implement a faster algorithm or more efficient storage method, but you wouldn't have to change the template files. They still get their "content" from the same "place" and don't need to concern themselves with what happens inside each black box.

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

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

It is worth noting that there is nothing to stop you from adopting a well structured approach to content construction using Text::Template or one of the other fine template processing modules available. Many people do indeed develop content using these tools in such a way as to promote reusability and maintainability every bit as much as the Template Toolkit does. The benefit of using the toolkit is that much of this is done for you. You get to reap the benefits of template caching (resulting in fast runtime processing), automatic error detection and handling, variable localisation and namespacing, dynamic loading of external modules, and so on, without having to code it yourself or even worry about the specifics of implementation. The details are hidden away, the directive syntax is simplified and you can get a lot done very quickly with the minimum of fuss.

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

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 specifying import tag sets as parameters to the use Template statement.

    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 method returns 1 if the template was successfully processed or 0 if an error occurred. 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";

The PRE_PROCESS and POST_PROCESS options may be used to specify the name(s) of template file(s) that should be processed immediately before and after each template, respectively. This can be used to add page headers and footers, for example.

TEMPLATE SYNTAX AND DIRECTIVES

DIRECTIVE TAGS

The default syntax for embedding directives in template documents is to enclose them within the character sequences '[%' and '%]'.

    [% 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

You can change the tag characters using the START_TAG, END_TAG and TAG_STYLE options, described below. You can also use the TAGS directive to change the tags on a per-file basis. The new tag definitions last only for the current template file. The TAGS directive should contain two whitespace delimited character sequences to represent the START and END tags.

    [% TAGS <!-- --> %]
    <!-- INCLUDE header title = 'Hello World!' -->

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 CALL directive is similar to GET in evaluating the variable named, but doesn't print the result returned. This can be useful when a variable is bound to a sub-routine or object method which you want to call but aren't interested in the value returned (especially if it returns 0 or some other status code). See "VARIABLES BOUND TO USER CODE" and "VARIABLES BOUND TO OBJECTS" below, for further details.

    [% CALL inc_page_counter %]

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, WHILE, BLOCK, FILTER, CATCH and PERL 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.

    [% 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 %]

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 
    %]

Note that the TAGS directive must always be specified in a tag by itself.

The IF, UNLESS, FOREACH, WHILE and FILTER 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:

    GET, SET, CALL, DEFAULT, INCLUDE, PROCESS, IMPORT, FILTER, USE
    FOR, FOREACH, IF, UNLESS, ELSE, ELSIF, AND, OR, NOT 
    BLOCK, MACRO, END, THROW, CATCH, ERROR, RETURN, STOP, PERL
    DEBUG

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 construct compound ("dotted") variables . Each element denotes a separate variable "namespace" which 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">Home</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
    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
       }
    %]

The 'keys' and 'values' methods may be applied to any hash to return lists of the hash keys and values.

    [% FOREACH field = product.keys %]
       [% field %] [% product.${field} %]
    [% END %]

This example also shows how a variable ('field' in this case) may be evaluated as '${field}' to return a value which is then used to index into the 'product' hash array.

You can copy all the members of a hash into the top level variable namespace with the IMPORT directive.

    [% user = {
         name = 'John Doe'
         id   = 'jdoe'
       }
    %]
   
    [% IMPORT user %] 
    Name: [% name %]   ID: [% id %]

You can automatically IMPORT a hash when INCLUDE'ing another template file or block by assigning it to the upper case IMPORT variable, passed as a parameter.

    [% BLOCK one %]
       [% user.name %] [% user.email %]
    [% END %]
  
    [% BLOCK two %]
       [% name %] [% email %]
    [% END %]
  
    [% user  = { name = 'me',  email = 'me@here.com'   }
       other = { name = 'you', email = 'you@there.com' }
    %]
  
    [% INCLUDE one %]
    [% INCLUDE one user=other %]
    [% INCLUDE two IMPORT=user %]
    [% INCLUDE two IMPORT=other %]

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

The basic binary mathematic operators (+ - * div and mod) can also be used.

    [% ten    = 10 
       twenty = 20
       thirty = twenty + ten
       forty  = 2 * twenty 
       fifty  = 100 div 2
       six    = twenty mod 7
    %]

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" ]
    %]

You can also create simple numerical sequences using the familiar '..' operator:

    [% n = [ 1 .. 4 ] %]    # 'n' is [ 1, 2, 3, 4 ] 

    [% x = 4
       y = 8
       z = [x..y]           # 'x' is [ 4, 5, 6, 7, 8 ]
    %]

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

When the FOREACH directive is used without specifying a target variable, any iterated values which are hash references will be automatically imported.

    # assume 'userlist' is a list of user hash refs
    [% FOREACH user = userlist %]
       [% user.name %]
    [% END %]
  
    # same as...
    [% FOREACH userlist %]
       [% name %]
    [% END %]

Note that this particular usage creates a localised variable context to prevent the imported hash keys from overwriting any existing variables. The imported definitions and any other variables defined in such a FOREACH loop will be lost at the end of the loop, when the previous context and variable values are restored.

The [% BREAK %] directive can be used to prematurely exit a FOREACH loop.

    [% FOREACH user = userlist %]
       [% user.name %]
       [% BREAK IF some.condition %]
    [% END %]

Individual elements of the list can be referenced by a numerical suffix. The first element of the list is element 0.

    [% list = [ 'one' 'two' 'three' 'four' ] %]
    [% list.0 %] [% list.3 %]

    [% FOREACH n = [0..3] %]
    [% list.${n} %], 
    [%- END %]

Output: one four one, two, three, four,

Several general purpose methods are defined for accessing elements or otherwise manipulating lists.

size

Returns the number of items in the list.

max

Returns the index number of the last entry in the list (size - 1).

first

Returns the first item in the list.

last

Returns the last item in the list.

sort

Returns the list items in basic sorted order (using Perl's 'sort').

join

Returns all elements in the list joined into a single string. A joining string can be specified as a parameter.

Example 1:

    [% list = [ 'Tom', 'Dick', 'Harry' ] %]
    [% FOREACH name = list.sort %]
       * [% name %]
    [% END %]

    or: [% list.sort.join(', ') %]

Output:

    3 names:
      * Dick
      * Harry
      * Tom

    or: Dick, Harry, Tom

Example 2:

    [% items  = [ 'alpha', 'bravo', 'charlie', 'whisky', 'zulu' ] %]
    [% items.size %] entries ([% items.first %] - [% items.last %]):
       -> [% items.join(', ') %]

Output:

    5 entries (alpha - zulu):
       -> alpha, bravo, charlie, whisky, zulu

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

In this example, the [% magic %] variable is bound to the do_magic() sub-routine. The code is called and the return value, 'Abracadabra', inserted into the document in place of the directive. The CALL directive can be used to evaluate a variable (e.g. call code or an object method) without printing the returned result.

   [% CALL some_code %]

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

    $data = {
        'foo'   => 'Mr. Foo',
        'bar'   => 'Mr. Bar',
        'qux'   => 'Qux',
        'bold'  => sub { my $text = shift; return "<b>$text</b>"; },
    }

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

myfile:

    [% bold('face') %]

Output:

    <b>face</b>

Named parameters may also be specified. These are automatically collected into a single hash array which is passed by reference as the last parameter to the sub-routine. Note how '=>' is synonymous for '='.

    [% whatever(foo, bar, name = 'John Doe', id = 'jdoe') %]

       # calls whatever('Mr. Foo', 'Mr. Bar', 
                        { name => 'John Doe', id => 'jdoe' });

    [% whatever(name => 'John Doe', id => 'jdoe') %]

       # calls whatever({ name => 'John Doe', id=>'jdoe' });

    [% whatever(10, name='John Doe', 20, id='jdoe') %]

       # calls whatever(10, 20, { name => 'John Doe', id=>'jdoe' });

The last example demonstrates the re-ordering of parameters. For the sake of clarity, it is recommended that you specify named parameters at the end of the list.

    [% whatever(10, 20, name='John Doe', id='jdoe') %]

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. Examples:

    return 'foo';
    return [ 'foo', 'bar' ];
    return $myobj;

If a sub-routine returns multiple values of which the first has some defined value, then the entire list will be folded into a list reference and taken as the value for the variable to which it is bound. Thus, the following are roughly equivalent:

    return ('foo', 'bar', 'baz');
    return ['foo', 'bar', 'baz'];

An undefined value may be returned by itself and will silently be converted to an empty string unless the DEBUG option is enabled, in which case an 'undef' exception will be raised. Where an undefined value is returned followed by another value, then that second value is taken to indicate an error condition. This may be in the form of a status code, an error string or a Template::Exception object reference. Note that returning an undefined first value disables the automatic list folding described above.

    return (undef, STATUS_OK);              # no error
    return (undef, STATUS_STOP);            # stop
    return (undef, 'something failed');     # general error
    return (undef, Template::Exception->new('DBI', $DBI::Errstr));

A status code of 0 (STATUS_OK) means everything went OK, and there's no error to raise. 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). A text string returned, such as in the third example above, is converted into a Template::Exception of type 'undef'. Template::Exception objects can also be returned directly as shown in the last example.

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 %]
       <!-- Database error handler -->
       <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 compound '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 another
             object which acts as an interface to a database
    'abw'    is a method called on the above object, caught by AUTOLOAD
             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
    %]

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 object mentioned in the previous example, if one is not provided.

    package MyObj;
  
    sub user {
        my ($self, $uid) = @_;
        return $uid ? $self->get_record($uid) : $self
    }

    sub AUTOLOAD {
        my ($self, @params) = @_;
        my $name = $AUTOLOAD;
        $name =~ s/.*:://;
        return if $name eq 'DESTROY';
        $self->get_record($name);
    }

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 created and returned for use in a FOREACH directive. The following pseudo-code example illustrates how a database iterator might perform. The 'userlist' method first determines a list of valid user ID's from a database table and then creates an iterator to step through them in sequence. On each iteration, the ACTION for the iterator is called, which in this case is a closure which calls the user($uid) method to retrieve the complete user record from the database. Thus, we avoid the overhead of loading and storing every complete user record, retrieving them only as and when required.

    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 be changed in the template:

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

A reference to the iterator is always available within a FOREACH block via the 'loop' variable. An iterator is automatically created by the FOREACH directive if a regular list is specified. The iterator provides a number of methods for testing the state of the loop: first() and last() return true if the iterator is on the first or last iteration of the loop; size() and max() return the number of elements and maximum index (size - 1) for the list; and number() and index() return the current iteration offset from 1 and 0 respectively (i.e. number() runs from 1 to size(), index() runs from 0 to max())

    [% FOREACH user = myorg.userlist %]
       [% INCLUDE utab_header IF loop.first() %]
       <tr> 
         <td>[% loop.number %]</td> <td>[% user.name %]</td>
       </tr>
       [% "</table>" IF loop.last() %]
    [% END %]

    [% BLOCK utab_header %]
    <table>
    <th>Number</th> <th>Name</th>
    [% END %]

CONDITIONAL BLOCKS

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 %]

The WHILE directive can be used to repeatedly process a template block while an expression (as per the examples above) evaluates "true".

    [% WHILE total < 100 %]
       ....
       [% total = calculate_new_total %]
    [% END %]

An assignment can be enclosed in parenthesis to evaluate the assigned value.

    [% WHILE (user = get_next_user_record) %]
       [% user.name %]
    [% END %]

The [% BREAK %] directive can be used to prematurely exit a WHILE loop.

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 first parameter to the INCLUDE directive is assumed to be the name of a file or defined block (see BLOCK, below). For convenience, it does not need to be quoted as long as the name contains only alphanumeric characters, underscores, dots or forward slashes. Names containing any other characters should be quoted.

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

To evaluate a variable to specify a file/block name, explicitly prefix it with a '$' or use double-quoted string interpolation.

    [% language = 'en'
       header   = 'test/html/header.html' 
    %]

    [% INCLUDE $header %]
    [% INCLUDE "$language/$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.

You should always use the '/'character as a path separator as shown in the above examples, regardless of your local operating system convention. Perl will automatically convert this to the local equivalent for non-Unix file systems. The '/' character is therefore portable across all platforms.

The included template will "inherit" all variables currently defined in the including template. Note how the 'title' and 'bgcol' variables in this next example are used in the 'header' file, inheriting the values defined previously in the including template.

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

header:

    <html>
    <head><title>[% title %]</title></head>
    <body bgcolor="[% bgcol %]">

Output:

    <html>
    <head><title>Hello World!</title></head>
    <body bgcolor="#ffffff">

The DEFAULT directive can be useful for supplying default values in commonly used template files such as this:

header:

    [% DEFAULT
       title = 'The "Hello World!" Web Site'
       bgcol = '#ffffff'
    -%]
    <html>
    <head><title>[% title %]</title></head>
    <body bgcolor="[% bgcol %]">

(Note how the DEFAULT directive specifies an explicit POST_CHOMP by placing a '-' immediately before the '%]' end-of-tag characters. This tells the processor to remove the whitespace and newline that immediately follow the DEFAULT directive. One place where additional whitespace can cause problems in an HTML document is before the initial <html> tag, so we're sure to strip it out, just to be safe)

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

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

Output:

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

These variables, along with any other non-compound variables that might be created or used within the included template remain local to it. Changes made to them don't affect the variables in the including template, even though they may have inherited values from them.

    [% 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'

Dotted compound variables behave slightly differently. The localisation process (known as "cloning the stash" but you won't be tested on that) only copies top-level variables. Any namespaces already defined will be accessible within a localised context, but the sub-namespace variables to which they refer will not be localised. In implementation terms, the references to hashes are copied, but the copies refer to the same hash. In more general terms, you can think of a dotted variable as referring to the appropriate global variable if (and only if) the top-level namespace (i.e. the first element of the compound variable) is already defined.

Let's see if an example makes this any clearer:

    [% user = { name = 'John Doe' } %]
    [% INCLUDE change_name %]
    Name is: [% user.name %]

change_name:

    [% user.name = 'Jack Herer' %]

Output:

    Name is: Jack Herer

A namespace that isn't already defined will be created automatically when used. This does remain local to the context of the current template. The following example demonstrates the kind of "unexpected" behaviour that you might encounter if you find yourself trying to set a variable in a namespace that doesn't already exist.

    [% INCLUDE change_name %]   
    User: [% user.name %]           # not defined

change_name:

    [% user.name = 'Tom Thumb' %]

In the change_name template, the 'user' variable is undefined so a namespace hash is created in the local context with a 'name' member set to 'Tom Thumb'. At the end of processing change_name, the local variables, including the 'user' namespace are deleted. This is also the case if an existing non-namespace variable exists. A local namespace will be created masking the previously defined value but only for the processing lifetime of that template.

    [% user = 'Tom Thumb' %]
    [% INCLUDE change_name %] 
    User: [% user %]           # prints "Tom Thumb"

change_name:

    # create a local 'user' namespace, masking 'Tom Thumb'
    [% user.name = 'Jack Herer' %]

If you find yourself setting global variables from within INCLUDE'd templates then you might want to use the pre-defined 'global' namespace. This is always pre-defined and globally accessible to every template.

    [% INCLUDE global_change_name %]
    [% global.sysname %]       # prints "Badger"

global_change_name:

    [% global.sysname = 'Badger' %]

Alternately, you might find the PROCESS directive to be more appropriate. The PROCESS directive is similar to INCLUDE in all respects except that it does not perform any localisation of variables. Changes made to variables in the sub-template, and indeed any variable definitions specified in the directive, will affect the including template. What you see is what you get.

    [% name = 'foo'
       age  = 100
    %] 
    [% PROCESS change_name  age = 101 %]
    Name is now '[% name %]' and age is [% age %] 

Output:

    Name is 'foo'
    Changing 'foo' to 'bar'
    Name is now 'bar' and age is 101

This is generally useful for processing separate files that define various configuration values.

    [% PROCESS myconfig %]
    <img src="$images/mylogo.gif">

myconfig:

    [% server   = 'www.myserver.com'
       homepage = "http://$server/"
       images   = '/images'
    %]

Output:

    <img src="/images/mylogo.gif">

See also the PRE_PROCESS option which allows you to specify such a file that will automatically be processed before each template.

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. The block definition itself does not generate any output.

    [% INCLUDE tmpblk %]

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

Note that both PROCESS and INCLUDE will raise a 'file' exception if an attempt is made to recurse into the same template file (e.g. by calling [% INCLUDE myself %] from within the template 'myself'). The RECURSION option can be enabled to permit recursion for some special cases. It is assumed that you know what you're doing if you take this step.

DEFINING MACROS

The MACRO directive allows you to define a directive or directive block which is then repeatedly evaluated each time the macro is called.

    [% MACRO header INCLUDE header %]

    [% header %]   # => [% INCLUDE header %]

Macros can be passed named parameters when called. These values remain local to the macro.

    [% header(title='Hello World') %]  
                   # => [% INCLUDE header title='Hello World' %]

A MACRO definition may include parameter names. Values passed to the macros are then mapped to these local variables. Other named parameters may follow these.

    [% MACRO header(title) INCLUDE header %]

    [% header('Hello World') %]
    [% header('Hello World', bgcol='#123456') %]

equivalent to:

    [% INCLUDE header title='Hello World' %]
    [% INCLUDE header title='Hello World' bgcol='#123456# %]

A MACRO may preceed any directive and must conform to the structure of the directive.

    [% MACRO header IF frames %]
       [% INCLUDE frames/header %]
    [% ELSE %]
       [% INCLUDE header %]
    [% END %]

    [% header %]

A MACRO may also be defined as an anonymous BLOCK. The block will be evaluated each time the macro is called. A macro must be defined before it is used.

    [% MACRO header BLOCK %]
       ...content...
    [% END %]

    [% header %]

PLUGIN OBJECTS AND LIBRARIES

The USE directive can be used to load and initialise "plugin" extension modules.

    [% USE myplugin %]

A plugin is a regular Perl module that conforms to a particular object-oriented interface, allowing it to be loaded into and used automatically by the Template Toolkit. For details of this interface and information on writing plugins, consult Template::Plugin.

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 Foo.Bar  %]     #  => Template::Plugin::Foo::Bar

Various 'system' plugins are included with the Template Toolkit (see below and "TEMPLATE TOOLKIT PLUGINS". These can be specified in lower case and are mapped to the appropriate name.

    [% USE cgi   %]        # => Template::Plugin::CGI
    [% USE table %]        # => Template::Plugin::Table

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);

Named parameters may also be specified. These are collated into a hash which is passed by reference as the last parameter to the constructor, as per the general template code calling interface described earlier.

    [% USE Chat('guestroom', max=50, lines=20, features='none') %]
       ==> Template::Plugin::Chat->new($context, 'guestroom', 
                { max => 50, lines => 20, features => 'none' } );

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 Chat('guestroom') %]
    Cheezy Chat Room: [% Chat.roomname %]
    [% FOREACH line = Chat.messages %]
       [% line.author %]: [% line.text %]
    [% END %]

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

    [% USE guest = Chat('guestroom') %]
    Cheezy Chat Room: [% guest.roomname %]

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>

The URL plugin allows you to build dynamic URLs from a base part and optional query parameters.

    [% USE mycgi = URL('/cgi-bin/foo.pl', debug=1) %]
    <a href="[% mycgi %]">...
    <a href="[% mycgi(mode='submit') %]"...

Output:

    <a href="/cgi-bin/foo.pl?debug=1">...
    <a href="/cgi-bin/foo.pl?mode=submit&debug=1">...

The CGI plugin is an example of one which delegates to another Perl module. In this this case, it is to Lincoln Stein's CGI.pm module. All of the methods provided by CGI.pm are available via the plugin.

    [% USE CGI %]

    [% CGI.start_form %]

    [% CGI.checkbox_group(name   =>   'colours', 
                          values => [ 'red' 'green' 'blue' ])
    %]

    [% CGI.popup_menu(name   =>   'items', 
                      values => [ 'foo' 'bar' 'baz' ])
    %]

    [% CGI.end_form %]

Simon Matthews <sam@knowledgepool.com> has written a DBI plugin which provides an interface to Tim Bunce's DBI module (both available from CPAN). Here's a short example:

    [% USE DBI('DBI:mSQL:mydbname') %]

    [% FOREACH user = DBI.query('SELECT * FROM users') %]
       [% user.id %] [% user.name %] [% user.etc.etc %]
    [% END %]

See the 'TEMPLATE TOOLKIT PLUGINS' section below for more information on the plugins distributed with the toolkit or available from CPAN.

The LOAD_PERL option (disabled by default) provides a further way by which external Perl modules may be loaded. If a regular Perl module (i.e. not a Template::Plugin::* or other module relative to some PLUGIN_BASE) supports an object-oriented interface and a new() constructor then it can be loaded and wrapped automatically by a Template::Plugin object. The following example shows how the IO::File module might be used. Please note that this feature is still experimental.

    [% USE file = IO.File('/tmp/mydata') %]

    [% WHILE line = file.getline %]
       <!-- [% line %] -->
    [% END %]

EVALUATING PERL CODE

The PERL directive is used to mark the start of a block which contains Perl code for evaluation. The EVAL_PERL option must be enabled for Perl code to be evaluated. A 'perl' exception will be thrown otherwise.

Perl code is evaluated in the Template::Perl package. The $context package variable contains a reference to the current Template::Context object. Template output may be generated by the output() method, for example.

  [% PERL %]
     $context->output("This output generated by Perl code");
  [% END %]

The $stash variable contains a reference to the top-level stash object which manages template variables.

  [% PERL %]
     $stash->{'foo'} = 'Bar';
  [% END %]

  Foo is [% foo %]

Output Foo is Bar

The block may contain other directives which are evaluated first. The processed block output is then passed to Perl for evaluation.

  [% PERL %]
     $stash->{'people'} = join(', ', qw( [% foo %] [% bar %] ));
  [% END %]

Any error encountered during the evaluation of the Perl code will be thrown as a 'perl' exception.

POST-PROCESSING FILTERS

The FILTER directive can be used to post-process the output of a block. The following filters are avilable by default:

html

Converts the characters '<', '>' and '&' to '&lt;', '&gt;' and '&amp', respectively, protecting them from being interpreted as representing HTML tags or entities.

    [% FILTER html %]
    Binary "<=>" returns -1, 0, or 1 depending on...
    [% END %]

output:

    Binary "&lt;=&gt;" returns -1, 0, or 1 depending on...
html_para

This filter formats a block of text into HTML paragraphs. A sequence of two or more newlines is used as the delimiter for paragraphs which are then wrapped in HTML <p>...</p> tags.

    [% FILTER html_para %]
    The cat sat on the mat.

    Mary had a little lamb.
    [% END %]

output:

    <p>
    The cat sat on the mat.
    </p>

    <p>
    Mary had a little lamb.
    </p>
html_break

Similar to the html_para filter described above, but uses the HTML tag sequence <br><br> to join paragraphs.

    [% FILTER html_para %]
    The cat sat on the mat.

    Mary had a little lamb.
    [% END %]

output:

    The cat sat on the mat.
    <br>
    <br>
    Mary had a little lamb.
format(format)

The 'format' filter takes a format string as a parameter (as per printf()) and formats each line of text accordingly.

    [% FILTER format('<!-- %-40s -->') %]
    This is a block of text filtered 
    through the above format.
    [% END %]

output:

    <!-- This is a block of text filtered        -->
    <!-- through the above format.               -->
truncate(length)

Truncates the text block to the length specified, or a default length of 32. Truncated text will be terminated with '...' (i.e. the '...' falls inside the required length, rather than appending to it).

    [% FILTER truncate(21) %]
    I have much to say on this matter that has previously been said
    on more than one occassion.
    [% END %]

output:

    I have much to say...
repeat(iterations)

Repeats the text block for as many iterations as are specified (default: 1).

    [% FILTER repeat(3) %]
    Am I repeating myself?
    [% END %]

output:

    Am I repeating myself?
    Am I repeating myself?
    Am I repeating myself?
remove(string)

Searches the input text for any occurences of the specified string and removes them. A Perl regular expression may be specified as the search string.

    [% "The  cat  sat  on  the  mat" FILTER remove('\s+') %]

output:

    Thecatsatonthemat
replace(search, replace)

Similar to the remove filter described above, but taking a second parameter which is used as a replacement string for instances of the search string.

    [% "The  cat  sat  on  the  mat" FILTER replace('\s+'m '_') %]

output:

    The_cat_sat_on_the_mat
redirect(file)

The 'redirect' filter redirects the output of the block into a separate file, specified relative to the OUTPUT_PATH configuration item.

    [% FOREACH user = myorg.userlist %]
       [% FILTER redirect("users/${username}.html") %]
          [% INCLUDE userinfo %]
       [% END %]
    [% END %]
into(varname)

The 'into' filter allows you to capture the output of a block into a template variable.

    [% FILTER into('user_details') %]
       User: [% user.name %]
       [% INCLUDE userinfo %]
    [% END %]

    [% notify_new_user_details(user_details) %]

Additional filters may be provided via the FILTERS configuration option. Filters may also be added at any time via the register_filter($name, $factory) method. See Template::Filters for further information.

A filter that is created without any specific parameters will be cached and re-used whenever that same filter is required. Specifying parameters to a filter will always cause a new filter instance to be created.

    [% FILTER myfilter %]
       # calls 'myfilter' factory code
       Blah Blah Blah
    [% END %]
       
    [% FILTER myfilter %]
       # re-uses cached filter created above
       Cabbages
    [% END %]
  
    [% FILTER myfilter('foo') %]
       # calls 'myfilter' factory code, passing 'foo'
       Rhubarb
    [% END %]

Filters that are created with parameters will not be cached unless an alias is provided for them. The filter instance can then be re-used by specifying the alias.

    [% FILTER non_atomic = censor('nuclear') %]
       # creates and runs the filter, aliasing it to non_atomic
       ...contentus maximus...
    [% END %]
  
    [% FILTER non_atomic %]
       # re-uses cached non_atomic filter created above
       ...ditto contentus...
    [% END %]

FILTERS may be nested within other filters. Multiple FILTER definitions may be added after other (non-block) directives.

    [% FILTER this_way %]
       ...content...
       [% FILTER that_way %]
          ...blah...
       [% END %]
    [% END %]

    [% INCLUDE myfile FILTER myfilter FILTER format('<!-- %s -->') %]

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. Note that you need to specify :status as a parameter to use Template in order for the STATUS_* constants to be defined.

    use Template qw( :status );

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

As from version 1.00, exception types may also be dotted values, e.g. 'foo.bar'. If a specific handler does not exist for the exception type, then elements of the name are progressively stripped from the end until a handler is found that represents the remaining part. An exception type 'foo.bar' could thus be handled by a 'foo.bar' or 'foo' handler. The 'default' handler will be used, if it exists, as a last resort.

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 occurred (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 up 'Feeling Sick' %]

Output:

    PROCESSING ERROR: up: Feeling Sick

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 occurred.

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 occurred</b>
       <br>
       Error: [% e.info %]
       <br>
       We apologise for the inconvenience.  The cleaning lady 
       has removed the server power to plug in her vacuum cleaner.
       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 specified as a reference to a list or as a single string, delimited by ':' ($Template::Cache::PATHSEP) Each item in a list may have additional CACHE parameters associated with it. If no INCLUDE_PATH is specified then the current working directory (i.e. '.') is assumed by default.

    my $cache = Template::Cache->new({
        INCLUDE_PATH => '/user/abw/templates:/user/abw/tmp',
    });
  
    my $cache = Template::Cache->new({
        INCLUDE_PATH => [ '/tmp/templates', '/usr/web/templates' ],
    });
  
    my $template = Template->new({
        INCLUDE_PATH => [ 
            '/user/web/templates/src:/usr/web/templates/elements'
            '/user/web/templates/toodarnbig' => { CACHE => 0 },
        ],
    });
  
    use Template::Cache;
    $Template::Cache::PATHSEP = ';';
    my $template = Template->new({
        INCLUDE_PATH => 'c:/templates;c:/web/templates'
    });
ABSOLUTE_PATHS

This option is enabled by default and allows templates to be specified using absolute paths. In this context, an absolute path is one which starts with '/'. Note that it is generally best to always use '/' as a directory delimiter, regardless of your local operating system convention. Perl will automatically convert forward slashes into the appropriate character.

Any false value will disable the option. In this case, any attempt to process a template file by specifying an absolute path will generate an error in the form of a 'file' exception (see CATCH). Files specified with a leading period (e.g. './foo/bar.html') are treated as relative to the current working directory. All other files are considered relative to one of the INCLUDE_PATH directories.

    # ABSOLUTE_PATHS are enabled by default
    $template->process("/slash/bang/wallop")          # OK
        || die $template->error();

    # in a template file, it would look like this
    [% INCLUDE /slash/bang/wallop %]                  # OK

    # this time we'll disable them
    my $t2 = Template->new({ ABSOLUTE_PATHS => 0 });

    $t2->process("foo/bar.html");                     # OK 
        || die $t2->error();

    $t2->process("/foo/bar.html")      # FAILS with 'file' exception
        || die $t2->error();           # reports

    # nope, this would barf
    [% INCLUDE /foo/bar.html %]        # FAILS with 'file' exception
PRE_DEFINE

A reference to a hash of variables and values that should be pre-defined for use in every template processed via the process() method. The original values are restored 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'   },
      }
  });
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">
EVAL_PERL

The EVAL_PERL option is used to specify if PERL sections should be evaluated or not. It is disabled by default and any PERL sections will raise 'perl' exceptions when encountered. Setting it to any true value permits code contained within such blocks to be evaluated.

PRE_PROCESS, POST_PROCESS

These values may be set to contain the names of template files (relative to INCLUDE_PATH) which should be processed immediately before and/or after each template. These do not get added to templates processed into a document via the INCLUDE or PROCESS tags. The PRE_PROCESS and POST_PROCESS are evaluated in the same variable context as the main document and so may define, update or delete variables for subseqent use.

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 %]
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 %% ... %%

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.

See also the TAGS directive which allows directive tags to set from within a template and act on a per-file basis.

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.

LOAD_PERL

The LOAD_PERL option modifies the behaviour of the USE directive. By default (LOAD_PERL => 0), the directive will only load special 'plugin' modules whose names map onto Perl modules in the 'Template::Plugin' namespace (e.g. CGI => Template::Plugin::CGI).

When the LOAD_PERL option is set to any true value, the directive will also attempt to load a regular Perl module (i.e. no namespace prefix added) and create an object instance via the new() method. The resulting object is then wrapped in a Template::Plugin object which delegates all method calls to it. This acts as a general interface between the underlying Perl object and the Template Toolkit.

The end result is that it is often possible to load a general purpose, object-oriented Perl module and use it in a template without having to write any special purpose plugin code.

This feature is new as of version 1.03 and is still largely experimental. Please report any problems or difficulties you may encounter to the author.

PLUGIN_BASE

This option allows you to define a base package for plugin objects loaded and used via the USE directive. The default value 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 Magic.Wand %]

Would request and instantiate and object from the plugin module 'Template::Plugin::Magic::Wand'.

Specifying a new PLUGIN_BASE will cause the processor to use that package name before falling back on the default 'Template::Plugin'.

    my $tproc = Template->new({
        PLUGIN_BASE => 'MyOrg::Template::Plugin',
    });

In the above example, the [% USE Magic.Wand %] directive, would resolve to 'MyOrg::Template::Plugin::Magic::Wand' or 'Template::Plugin::Magic::Wand' in that order. Thus, a module defined in a 'local' PLUGIN_BASE will be used in preference to the default Template Toolkit equivalent. In other words, the default 'Template::Plugin' location is always searched, but after any user defined values.

If the LOAD_PERL option is set, then the directive will also attempt to load the module without adding a package prefix (i.e. a regular Perl module) and instantiate an object via the new() method. This is wrapped in a Template::Plugin object.

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;
    my $factory = MyOrg::Template::Plugin::Foo->new();
  
    my $template->new({ 
        PLUGINS => {
          'womble' => 'MyOrg::Template::Plugin::Womble',
          'foo'    =>  $factory,
        }
    });

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 also 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 foo('xyz') %]
      ==> $factory->new($context, 'xyz');

This approach facilitates the easy implementation and use of plugins that act as singletons (one instance only) or share some state information.

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.

FILTERS

The FILTERS option may contain a reference to a hash defining additional filter types. Each key represents a filter name and the value should contain a CODE reference which will be called when the relevant FILTER directive is encountered, passing any additional parameters specified. This sub-routine is expected to act as a factory and construct a closure, or return a reference to some other code, which will be responsible for filtering the text.

    $tproc = Template->new({
        FILTERS => {
            'microjive' => sub { \&microjive },
            'censor'    => \&make_censor_filter,
        },
    });
  
    # 'static' filter which never takes params (like 'html')
    sub microjive {
        my $text = shift;
        $text =~ s/microsoft/The 'Soft/sig;
        $text;
    }
    
    # factory for 'dynamic' filters which can take params
    sub make_censor_filter {
        my @forbidden = @_;
        return sub {
            my $text = shift;
            foreach my $word (@forbidden) {
                $text =~ s/$word/**CENSORED**/sig;
            }
            return $text;
        }
    }

Example:

    [% FILTER microjive %] 
    The "Halloween Document", leaked to Eric Raymond 
    from an insider at Microsoft, demonstrated...
    [% END %]              
  
    [% FILTER censor('nuclear') %]
    Airkraft were forced to fly in nuclear winds 
    but still managed an excellent performance.
    [% END %]

Output:

    The "Halloween Document", leaked to Eric Raymond 
    from an insider at The 'Soft, demonstrated...

    Airkraft were forced to fly in **CENSORED** winds 
    but still managed an excellent performance.
OUTPUT_PATH

This option can be used to define a directory to which output files should be written. By default, output is sent to STDOUT, but may be directed to a file by specifying the OUTPUT option or by passing a third parameter to the process() method. The default value for OUTPUT_PATH is '.', representing the current working directory.

    $tproc = Template->new({
        INCLUDE_PATH => '/tmp/src',
        OUTPUT_PATH  => '/tmp/dest',
    });

    my $params = { 'baz' => 'Qux' };

    foreach $file ('foo', 'bar') {
        $tproc->process($file, $params, $file)
            || warn "Error in $file: ", $tproc->error(), "\n";
    }

This example would process the files /tmp/src/foo and /tmp/src/bar, writing the output to /tmp/dest/foo and /tmp/dest/bar respectively.

OUTPUT, ERROR

The OUTPUT and ERROR options may be specified to redirect template output and/or error messages. The values for these options may be one of; a plain string indicating a filename which will be opened (relative to OUTPUT_PATH) and written to; a file GLOB opened ready for output; a reference to a scalar to which output/error is appended; or any object reference which implements a 'print' method. This final option allows IO::Handle, Apache::Request, or other such objects to be passed in directly.

    my $output = '';

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

In an Apache/mod_perl handler:

    sub handler {
        my $r    = shift;
        my $file = $r->path_info();

        my $template = Template->new({ OUTPUT => $r });

        $template->process($file) || do {
            $r->log_reason($template->error());
            return SERVER_ERROR;
        };

        return OK;
    }

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    - a 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();
    });
RECURSION

The template processor will raise a file exception if it detects direct or indirect recursion into a template. Setting this option to any true value will permit such recursion.

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, $output, $error)

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 optional third and fourth parameters may be used to specify alternate output and error locations for the processing of this template file only, temporarily over-riding any existing OUTPUT and ERROR values (existing file handles remain open and intact). See redirect() below for information on what the values may contain.

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.

The name of the template file is stored in the template variable 'filename'. This will not be the case if a 'filename' variable has been otherwise defined, or if the $template specified is a reference and does not represent a filename.

  This file: [% filename %]

redirect($what, $where)

The redirect() method can be called to redirect the output or error stream for the template processing system. Redirections can also be established when the object is created with the OUTPUT and ERROR options.

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 name (relative to OUTPUT_PATH), a reference to a scalar variable to which output is appended, a code reference which is called to handle output, or any object that supports a print method.

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.

TEMPLATE TOOLKIT PLUGINS

The following plugin modules are distributed with the Template Toolkit.

Format

The Format plugin provides a simple way to format text according to a printf()-like format.

    [% USE bold = format('<b>%s</b>') %]
    [% bold('Hello') %]
URL

The URL plugin provides a simple way of contructing URLs from a base part and a variable set of parameters. See Template::Plugin::URL for further details.

    [% USE mycgi = url('/cgi-bin/bar.pl', debug=1) %]

    [% mycgi %]
       # ==> /cgi/bin/bar.pl?debug=1

    [% mycgi(mode='submit') %]
       # ==> /cgi/bin/bar.pl?mode=submit&debug=1
Table

The Table plugin allows you to format a list of data items into a virtual table by specifying a fixed number of rows or columns, with an optional overlap. See Template::Plugin::Table for further details.

    [% USE table(list, rows=10, , overlap=1) %]

    [% FOREACH item = table.col(3) %]
       [% item %]
    [% END %]
CGI

The CGI plugin is a wrapper around Lincoln Stein's <lstein@genome.wi.mit.edu> CGI.pm module. The plugin is distributed with the Template Toolkit (see Template::Plugin::CGI) and the CGI module itself is distributed with recent versions Perl, or is available from CPAN.

XML::DOM

The XML::DOM plugin gives access to the XML Document Object Module via Clark Cooper <cooper@sch.ge.com> and Enno Derksen's <enno@att.com> XML::DOM module. The plugin is distributed with the Template Toolkit (see Template::Plugin::XML::DOM) and requires the XML::DOM module, available from CPAN:

  http://www.cpan.org/modules/by-module/XML
XML::RSS

The XML::RSS plugin is a simple interface to Jonathan Eisenzopf's <eisen@pobox.com> XML::RSS module. An RSS (Rich Site Summary) file is typically used to store short news 'headlines' describing different links within a site. This plugin allows you to parse RSS files and format the contents accordingly using templates. The plugin is distributed with the Template Toolkit (see Template::Plugin::XML::RSS) and requires the XML::RSS module, also available from CPAN:

  http://www.cpan.org/modules/by-module/XML

The following module is distributed separately from the Template Toolkit.

DBI

Simon Matthews <sam@knowledgepool.com> has developed a DBI plugin for the Template Toolkit which brings the full power of Tim Bunce's <Tim.Bunce@ig.co.uk> database interface module (DBI) to your templates. The DBI plugin and the DBI modules themselves are available from CPAN at:

  http://www.cpan.org/authors/id/S/SA/SAM/
  http://www.cpan.org/modules/by-module/DBI/

EXAMPLES

These examples illustrate some of the typical uses of Template Toolkit directives.

    # include another template, passing "local" variables
    [% INCLUDE header
       title = 'Hello World'
    %]

    # process "config" file to set some variables 
    [% PROCESS my_vardefs %]

    # iterate through 'userlist' list of hashrefs
    [% FOREACH user = userlist %]
       [% user.name %] [% user.email %]
    [% END %]

    # shorthand for above
    [% INCLUDE userinfo.html FOREACH user = userlist %]
    [% INCLUDE "$user.id/info.html" FOREACH user = userlist %]

    # conditional block
    [% IF graphics %]
       [% INCLUDE gratuitous_logo %]
    [% END %]

    # define a template block
    [% BLOCK table_row %]
       <td>[% name %]</td> <td>[% email %]</td>
    [% END %]

    # INCLUDE the defined block 
    [% INCLUDE table_row  name='me'  email='me@here.org'   %]
    [% INCLUDE table_row  name='you' email='you@there.org' %]
    [% INCLUDE table_row FOREACH userlist %]

    # example of the 'format' plugin...
    [% USE bold = format('<b>%s</b>') %]
    [% bold('This is bold') %]

    # ...and any other plugins...
    [% USE myplugin %]
    [% myplugin.does_this %]
    [% myplugin.does_that(foo, bar, baz) %]   

    # html filter 'escapes' characters '<', '>' and '&'
    [% FILTER html %]
       The value for Xyzzyx is < 100
       ...
    [% END %]

    [% "$user.name showed that x < y && z > 0" FILTER html %]

    # define a block to be processed when 'myerror' is thrown
    [% CATCH myerror %]
       <b>A strange and mystical error has occurred.</b>
       <ul>
          [% e.type %]: [% e.info %]
       </ul>

       [% # report error to STDERR/logfile/etc., cleanup and stop %]
       [% ERROR "myerror occurred: $e.info" %]
       [% INCLUDE footer %]
       [% STOP %]
    [% END %]

    # throw a 'myerror' exception
    [% THROW myerror 'The warp core has been breached' %]

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 and ttree
    doc/        Documentation source
    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.

Example:

    use lib qw( . ./t ../lib );
    use Template::Test;

    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 you may need to seek help elsewhere. :-)

AUTHOR

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

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

VERSION

This is version 1.05 of the Template Toolkit.

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.

The latest version of the Template Toolkit can be downloaded from any CPAN site:

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

Information regarding interim and development versions is posted to the templates mailing list.

COPYRIGHT

Copyright (C) 1996-2000 Andy Wardley. All Rights Reserved. Copyright (C) 1998-2000 Canon Research Centre Europe Ltd.

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. (http://www.knowledgepool.com/).

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, fixes and features to both Text::MetaText and the Template Toolkit and they all deserve credit for having improved the end product in some way and their efforts continue to be very much appreciated. In particular, Simon Matthews <sam@knowledegpool.com>, aka "SAM", deserves special mention (and wins many beer tokens) for his continued effort and interest over a number of years. Please let me know if you think anyone is missing from this list.

  Thiery-Michel Barral      <kktos@electron-libre.com>
  Neil Bowers               <neilb@cre.canon.co.uk>
  Francois Desarmenien      <desar@club-internet.fr>
  Horst Dumcke              <hdumcke@cisco.com> 
  Perrin Harkins            <pharkins@etoys.com>
  Hans von Lengerke         <hans@lengerke.org>
  Jonas Lilligren           <jonas@paranormal.o.se>
  Simon Matthews            <sam@knowledgepool.com>
  Leslie Michael Orchard    <deus_x@ninjacode.com>
  Eugene Miretskiy          <eugene@invision.net>
  Martin Portman            <mrp@cre.canon.co.uk>
  Paul Sharpe               <paul@miraclefish.com>
  Doug Steinwand            <dsteinwand@etoys.com>

RELATED MODULES AND PROJECTS

Simon Matthews <sam@knowledgepool.com> has developed a DBI plugin for the Template Toolkit which brings the full power of Tim Bunce's <Tim.Bunce@ig.co.uk> database interface module (DBI) to your templates. The DBI plugin and the DBI modules themselves are available from CPAN at:

  http://www.cpan.org/authors/id/S/SA/SAM/
  http://www.cpan.org/modules/by-module/DBI/

Leslie Michael Orchard <deus_x@ninjacode.com> is developing Iaijutsu, a fully featured web application server and content management system which uses the Template Toolkit for processing content templates. For further information, see:

  http://www.ninjacode.com/iaijutsu

Horst Dumcke <hdumcke@cisco.com> is working on Istore (Information Storage and Retrieval), a Perl module which separates content, directory structure and presentation. The 'presentation' part is provided in part by the Template Toolkit. See

  http://www.employees.org/~hdumcke/IStore/

Paul Sharpe <paul@miraclefish.com> is the author of DBFramework, a collection of classes for manipulating DBI databases loosely based on the CDIF Data Model Subject Area. He's currently in the process of reworking it to use the Template Toolkit as the presentation layer. The module is available from CPAN in

  http://www.cpan.org/modules/by-module/DbFramework/

SEE ALSO

A mailing list exists for up-to-date information on the Template Toolkit and for following and contributing to the development process. Send email to majordomo@cre.canon.co.uk with the following message in the body:

    subscribe templates

The tpage and ttree scripts are distributed and installed along with the Template Toolkit. The tpage script simply processes named files or STDIN if unspecified, using a default Template object. The ttree script can be used to process entire directory trees of templates, allowing large content systems such as web sites to be rebuilt from a single command or configuration file.

    perldoc tpage
    perldoc ttree

The Template::Tutorial document provides an introduction to the Template Toolkit and shows some typical examples of usage.

    perldoc Template::Tutorial

The following modules comprise the Template Toolkit. Consult the individual documentation for further details.

Template::Context

The Template::Context module defines a class of objects which each represent a unique run-time environment in which templates are rendered. The context maintains references to the stash of variables currently defined (Template::Stash) and to a cache object (Template::Cache) which provides access to template files. It also defines the output() method through which template output is directed and provides the error() and throw() methods for error handling. The main process() method is called to render a template within the context.

Template::Stash

The Template::Stash module defines an object class which is used for storing, retrieving and evaluating variables and their values for run-time access and processing by templates.

Template::Cache

The Template::Cache module defines an object class which is used to find, load, parse, compile and then cache template documents. The cache implements a simple fetch($template) method which will accept a wide range of inputs (filename, text ref, GLOB, IO::Handle, etc) and attempt to read the template and call on a Template::Parser to parse and compile it to an internal form. This is then cached for subsequent fetch() calls for the same template.

Template::Parser

The Template::Parser module defines an object class which implements the template parser and compiler. The template text is first scanned by a Perl regex which breaks the text into chunks and lexes the tokens within directive tags. A DFA (Deterministic Finite-State Automation) then iterates through the tokens using the rules and states defined in Template::Grammar and generates a compiled template document represented by the root node of a tree of Template::Directive objects. The rendering context may then call the process() method of the root node, passing itself as a reference, to render the template.

Template::Grammar

The Template::Grammar module defines the rules and state tables for the Template::Parser DFA. These are generated by the Parse::Yapp module. The Template-Toolkit distribution contains a parser directory which contains further files and information concerning the grammar and compilation thereof.

Template::Directive

The Template::Directive module defines a base class and a number of derived specialist classes to represent directives within template documents. These are instantiated by the Template::Parser object from actions defined in Template::Grammar.

Template::Exception

The Template::Exception module defines a primitive exception type for representing error conditions within the Template Toolkit.

Template::Iterator

The Template::Iterator module defines a data iterator which is used by the FOREACH directive. This may be sub-classed to create more specialised iterators for traversing data sets.

Template::Plugin

The Template::Plugin module defines a base class for Template Toolkit extension modules that can be loaded via the USE directive.

Template::Filters

A module which implements the FILTER methods.

Template::Constants

Defines various constants used in the Template Toolkit.

Template::Utils

Defines utility functions.

Template::Debug

Defines functions and methods for debugging (incomplete).