Template::Manual::Syntax - Directive syntax, structure and semantics


Template::Manual::Syntax - Directive syntax, structure and semantics


This section describes the syntax, structure and semantics of the Template Toolkit directives and general presentation language.

Tag Styles

By default, template directives are embedded within the character sequences '[%' and '%]'. e.g.

    [% PROCESS header %]

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

    [% PROCESS footer %]

You can change the tag characters using the START_TAG, END_TAG and TAG_STYLE configuration options. You can also use the TAGS directive to define a new tag style for the current template file.

You can also set the INTERPOLATE option to allow simple variable references to be embedded directly in templates, prefixed by a '$'.

    # INTERPOLATE => 0
    <td>[% name %]</td>  <td>[% email %]</td>
    # INTERPOLATE => 1
    <td>$name</td>  <td>$email</td>

Directives may be embedded anywhere in a line of text and can be split across several lines. Insignificant whitespace is generally ignored within the directive.

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

    [%INCLUDE menu align='right'%]

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


The '#' character is used to indicate comments within a directive. When placed immediately inside the opening directive tag, it causes the entire directive to be ignored.

    [%# this entire directive is ignored no
        matter how many lines it wraps onto

In any other position, it causes the remainder of the current line to be treated as a comment.

    [% # this is a comment
       theta = 20      # so is this
       rho   = 30      # <aol>me too!</aol>

Chomping Whitespace

You can add '-' or '+' to the immediate start or end of a directive tag to control the whitespace chomping options. See the PRE_CHOMP and POST_CHOMP options for further details.

    [% BLOCK foo -%]            # remove trailing newline
    This is block foo
    [%- END %]                  # remove leading newline

Implicit Directives: GET and SET

The simplest directives are GET and SET which retrieve and update variable values respectively. The GET and SET keywords are actually optional as the parser is smart enough to see them for what they really are (but note the caveat below on using side-effect notation). Thus, you'll generally see:

    [% SET foo = 10 %]
    [% GET foo %]

written as:

    [% foo = 10 %]
    [% foo %]

You can also express simple logical statements as implicit GET directives:

    [% title or template.title or 'Default Title' %]
    [% mode == 'graphics' ? "Graphics Mode Enabled" : "Text Mode" %]

All other directives should start with a keyword specified in UPPER CASE (but see the ANYCASE option). All directives keywords are in UPPER CASE to make them visually distinctive and to distinguish them from variables of the same name but different case. It is perfectly valid, for example, to define a variable called 'stop' which is entirely separate from the STOP directive.

    [% stop = 'Clackett Lane Bus Depot' %]
    The bus will next stop at [% stop %]    # variable
    [% STOP %]                              # directive

Block Directives

Directives such as FOREACH, WHILE, BLOCK, FILTER, etc., mark the start of a block which may contain text or other directives up to the matching END directive. Blocks may be nested indefinitely. 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 2000 [% me %]
       [% INCLUDE company/logo %]
    [% END %]

    [% IF foo %]
       [% FOREACH thing = foo.things %]
          [% thing %]
       [% END %]
    [% ELSIF bar %]
       [% INCLUDE barinfo %]
    [% ELSE %]
       do nothing...
    [% END %]

Block directives can also be used in a convenient side-effect notation.

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


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

Capturing Block Output

The output of a directive can be captured by simply assigning the directive to a variable.

    [% headtext = PROCESS header title="Hello World" %]
    [% people = PROCESS userinfo FOREACH user = userlist %]

This can be used in conjunction with the BLOCK directive for defining large blocks of text or other content.

    [% poem = BLOCK %]
       The boy stood on the burning deck,
       His fleece was white as snow.
       A rolling stone gathers no moss,
       And Keith is sure to follow.
    [% END %]

Note one important caveat of using this syntax in conjunction with side-effect notation. The following directive does not behave as might be expected:

    [% var = 'value' IF some_condition %]

In this case, the directive is interpreted as (spacing added for clarity)

    [% var = IF some_condition %]
    [% END %]

rather than

    [% IF some_condition %]
       [% var = 'value' %]
    [% END %]

The variable is assigned the output of the IF block which returns 'value' if true, but nothing if false. In other words, the following directive will always cause 'var' to be cleared.

    [% var = 'value' IF 0 %]

To achieve the expected behaviour, the directive should be written as:

    [% SET var = 'value' IF some_condition %]

Chaining Filters

Multiple FILTER directives can be chained together in sequence. They are called in the order defined, piping the output of one into the input of the next.

    [% PROCESS somefile FILTER truncate(100) FILTER html %]

The pipe character, '|', can also be used as an alias for FILTER.

    [% PROCESS somefile | truncate(100) | html %]

Multiple Directive Blocks

Multiple directives can be included within a single tag when delimited by semi-colons, ';'. Note however that the TAGS directive must always be specified in a tag by itself.

    [% IF title; 
          INCLUDE header; 
          INCLUDE other/header  title="Some Other Title";


    [% IF title %]
       [% INCLUDE header %]
    [% ELSE %]
       [% INCLUDE other/header  title="Some Other Title" %]
    [% END %]


Andy Wardley <abw@andywardley.com>



Template Toolkit version 2.10, released on 24 July 2003.


  Copyright (C) 1996-2003 Andy Wardley.  All Rights Reserved.
  Copyright (C) 1998-2002 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.

 Template::Manual::Syntax - Directive syntax, structure and semantics