Regular scalar variables are accessed by simply specifying their name. As these are just entries in the top-level variable hash they can be considered special cases of hash array referencing as described below, with the main namespace hash automatically implied.

[% article %]

Members of hash arrays are accessed by specifying the hash reference and key separated by the dot '.' operator.

Example data:

my $vars = {
    'home' => 'http://www.myserver.com/homepage.html',
    'page' => {
        'this' => 'mypage.html',
        'next' => 'nextpage.html',
        'prev' => 'prevpage.html',
    },
};

Example template:

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

Generated 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. The undefined value will be returned for any such variable accessed which the Template Toolkit will silently ignore (unless the DEBUG option is enabled).

Example data:

my $vars = {
    message => 'Hello World!',
    _secret => "On the Internet, no-one knows you're a dog",
    thing   => {
        public    => 123,
        _private  => 456,
        '.hidden' => 789,
    },
};

Example template:

[% message %]           # outputs "Hello World!"
[% _secret %]           # no output
[% thing.public %]      # outputs "123"
[% thing._private %]    # no output
[% thing..hidden %]     # ERROR: unexpected token (..)

You can disable this feature by setting the $Template::Stash::PRIVATE package variable to a false value.

$Template::Stash::PRIVATE = undef;   # now you can thing._private

To access a hash entry using a key stored in another variable, prefix the key variable with '$' to have it interpolated before use (see Variable Interpolation).

[% pagename = 'next' %]
[% page.$pagename %]       # same as [% page.next %]

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 this following example, the product variable automatically springs into life as a hash array unless otherwise defined.

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

The [% product.id %] [% product.desc %] 
costs $[% product.price %].00

Generated output:

The XYZ-2000 Bogon Generator 
costs $666.00

You can use Perl's familiar { ... } construct to explicitly create a hash and assign it to a variable. Note that commas are optional between key/value pairs and = can be used in place of =>.

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

# perl style
[% product = {
     id    => 'XYZ-2000',
     desc  => 'Bogon Generator',
     price => 666,
   }
%]

Items in lists are also accessed by use of the dot operator.

Example data:

my $vars = {
    people => [ 'Tom', 'Dick', 'Larry' ],
};

Example template:

[% people.0 %]          # Tom
[% people.1 %]          # Dick
[% people.2 %]          # Larry

The FOREACH directive can be used to iterate through items in a list.

[% FOREACH person IN people %]
Hello [% person %]
[% END %]

Generated output:

Hello Tom
Hello Dick
Hello Larry

Lists can be constructed in-situ using the regular anonymous list [ ... ] construct. Commas between items are optional.

[% cols = [ 'red', 'green', 'blue' ] %]

[% FOREACH c IN cols %]
   [% c %]
[% END %]

or:

[% FOREACH c IN [ 'red', 'green', 'blue' ] %]
   [% c %]
[% END %]

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

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

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

Template variables can contain references to Perl subroutines. When the variable is used, the Template Toolkit will automatically call the subroutine, passing any additional arguments specified. The return value from the subroutine is used as the variable value and inserted into the document output.

my $vars = {
    wizard  => sub { return join(' ', 'Abracadabra!', @_) },
};

Example template:

[% wizard %]                    # Abracadabra!
[% wizard('Hocus Pocus!') %]    # Abracadabra! Hocus Pocus!

Template variables can also contain references to Perl objects. Methods are called using the dot operator to specify the method against the object variable. Additional arguments can be specified as with subroutines.

use CGI;

my $vars = {
    # hard coded CGI params for purpose of example
    cgi  => CGI->new('mode=submit&debug=1'),
};

Example template:

[% FOREACH p IN cgi.param %]     # returns list of param keys
[% p %] => [% cgi.param(p) %]   # fetch each param value
[% END %]

Generated output:

mode => submit
debug => 1

Object methods can also be called as lvalues. That is, they can appear on the left side of an assignment. The method will be called passing the assigning value as an argument.

[% myobj.method = 10 %]

equivalent to:

[% myobj.method(10) %]

Subroutines and methods will be passed any arguments specified in the template. Any template variables in the argument list will first be evaluated and their resultant values passed to the code.

my $vars = {
    mycode => sub { return 'received ' . join(', ', @_) },
};

template:

[% foo = 10 %]
[% mycode(foo, 20) %]       # received 10, 20

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. Named parameters can be specified using either => or = and can appear anywhere in the argument list.

my $vars = {
    myjoin => \&myjoin,
};

sub myjoin {
    # look for hash ref as last argument
    my $params = ref $_[-1] eq 'HASH' ? pop : { };
    return join($params->{ joint } || ' + ', @_);
}

Example template:

[% myjoin(10, 20, 30) %]
[% myjoin(10, 20, 30, joint = ' - ' %]
[% myjoin(joint => ' * ', 10, 20, 30 %]

Generated output:

10 + 20 + 30
10 - 20 - 30
10 * 20 * 30

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) %]       # outputs "Romeo"

User code should return a value for the variable it represents. This can be any of the Perl data types described above: a scalar, or reference to a list, hash, subroutine or object. Where code returns a list of multiple values the items will automatically be folded into a list reference which can be accessed as per normal.

my $vars = {
    # either is OK, first is recommended
    items1 => sub { return [ 'foo', 'bar', 'baz' ] },
    items2 => sub { return ( 'foo', 'bar', 'baz' ) },
};

Example template:

[% FOREACH i IN items1 %]
   ...
[% END %]

[% FOREACH i IN items2 %]
   ...
[% END %]

Errors can be reported from user code by calling die(). Errors raised in this way are caught by the Template Toolkit and converted to structured exceptions which can be handled from within the template. A reference to the exception object is then available as the error variable.

my $vars = {
    barf => sub { 
        die "a sick error has occurred\n";
    },
};

Example template:

[% TRY %]
   [% barf %]       # calls sub which throws error via die()
[% CATCH %]
   [% error.info %]     # outputs "a sick error has occurred\n"
[% END %]

Error messages thrown via die() are converted to exceptions of type undef (the literal string "undef" rather than the undefined value). Exceptions of user-defined types can be thrown by calling die() with a reference to a Template::Exception object.

use Template::Exception;

my $vars = {
    login => sub { 
        ...do something...
        die Template::Exception->new( badpwd => 'password too silly' );
    },
};

Example template:

[% TRY %]
   [% login %]
[% CATCH badpwd %]
   Bad password: [% error.info %]
[% CATCH %]
   Some other '[% error.type %]' error: [% error.info %]
[% END %]

The exception types stop and return are used to implement the STOP and RETURN directives. Throwing an exception as:

die (Template::Exception->new('stop'));

has the same effect as the directive:

[% STOP %]

The template variable contains a reference to the main template being processed, in the form of a Template::Document object. This variable is correctly defined within PRE_PROCESS, PROCESS and POST_PROCESS templates, allowing standard headers, footers, etc., to access metadata items from the main template. The name and modtime metadata items are automatically provided, giving the template name and modification time in seconds since the epoch.

Note that the template variable always references the top-level template, even when processing other template components via INCLUDE, PROCESS, etc.

The component variable is like template but always contains a reference to the current, innermost template component being processed. In the main template, the template and component variable will reference the same Template::Document object. In any other template component called from the main template, the template variable will remain unchanged, but component will contain a new reference to the current component.

This example should demonstrate the difference:

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

foo template:

[% template.name %]         # foo
[% component.name %]        # foo
[% PROCESS footer %]

footer template:

[% template.name %]         # foo
[% component.name %]        # footer

Additionally, the component variable has two special fields: caller and callers. caller contains the name of the template that called the current template (or undef if the values of template and component are the same). callers contains a reference to a list of all the templates that have been called on the road to calling the current component template (like a call stack), with the outer-most template first.

Here's an example:

outer.tt2 template:

[% component.name %]        # 'outer.tt2'
[% component.caller %]      # undef
[% component.callers %]     # undef
[% PROCESS 'middle.tt2' %]

middle.tt2 template:

[% component.name %]        # 'middle.tt2'
[% component.caller %]      # 'outer.tt2'
[% component.callers %]     # [ 'outer.tt2' ]
[% PROCESS 'inner.tt2' %]

inner.tt2 template:

[% component.name %]        # 'inner.tt2'
[% component.caller %]      # 'middle.tt2'
[% component.callers %]     # [ 'outer.tt2', 'middle.tt2' ]

Within a FOREACH loop, the loop variable references the Template::Iterator object responsible for controlling the loop.

[% FOREACH item = [ 'foo', 'bar', 'baz' ] -%]
   [% "Items:\n" IF loop.first -%]
   [% loop.count %]/[% loop.size %]: [% item %]
[% END %]

Within a CATCH block, the error variable contains a reference to the Template::Exception object thrown from within the TRY block. The type and info methods can be called or the variable itself can be printed for automatic stringification into a message of the form "$type error - $info". See Template::Exception for further details.

[% TRY %]
   ...
[% CATCH %]
   [% error %]
[% END %]

The WRAPPER method captures the output from a template block and then includes a named template, passing the captured output as the 'content' variable.

[% WRAPPER box %]
Be not afeard; the isle is full of noises,
Sounds and sweet airs, that give delight and hurt not.
[% END %]

[% BLOCK box %]
<blockquote class="prose">
  [% content %]
</blockquote>
[% END %]