variables(3)

NAME

Template::Manual::Variables - Template variables and code
bindings

DESCRIPTION

This section describes the different ways in which Perl
data can be bound to template variables and accessed via
Template Toolkit directives.

Template Variables

A reference to a hash array may be passed as the second argument to the process() method, containing definitions of template variables. The VARIABLES (a.k.a. PRE_DEFINE) option can also be used to pre-define variables for all templates processed by the object.: my $tt = Template->new({
VARIABLES => {
version => 3.14,
release => 'Sahara',

},; });; my $vars = {
serial_no => 271828,; };; $tt->process('myfile', $vars);
'myfile':: This is version [% version %] ([% release %]).
Serial number: [% serial_no %]
output:: This is version 3.14 (Sahara)
Serial number: 271828
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. Upper case variable names are permitted, but not recommended due to a possible con flict with an existing or future reserved word. As of version 2.00, these are:: GET CALL SET DEFAULT INSERT INCLUDE PROCESS WRAP; PER
IF UNLESS ELSE ELSIF FOR FOREACH WHILE SWITCH CASE USE PLUGIN FILTER MACRO PERL RAWPERL BLOCK META TRY THROW CATCH FINAL NEXT LAST BREAK RETURN STOP CLEAR TO STEP AND OR NOT MOD DIV END
The variable values may be of virtually any Perl type, including simple scalars, references to lists, hash arrays, subroutines or objects. The Template Toolkit will automatically apply the correct procedure to accessing these values as they are used in the template.
Example:: my $vars = {
article => 'The Third Shoe',
person => {
id => 314,
name => 'Mr. Blue',
email => 'blue@nowhere.org',

},
primes => [ 2, 3, 5, 7, 11, 13 ],
wizard => sub { return join(' ', 'Abracadabra!',

@_) },
cgi => CGI->new('mode=submit&debug=1'),; };
template:: [% article %]; [% person.id %]: [% person.name %] <[% person.email; %]>; [% primes.first %] - [% primes.last %], including [%; primes.3 %]
[% primes.size %] prime numbers: [% primes.join(', '); %]; [% wizard %]
[% wizard('Hocus Pocus!') %]; [% cgi.param('mode') %]
output:: The Third Shoe; 314: Mr. Blue <blue@nowhere.org>; 2 - 13, including 7
6 prime numbers: 2, 3, 5, 7, 11, 13; Abracadabra!
Abracadabra! Hocus Pocus!; submit
Scalar Values
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 names pace hash automatically implied.: [% article %]
Hash Array References
Members of hash arrays are accessed by specifying the hash reference and key separated by the dot '.' operator.: my $vars = {
'home' => 'http://www.myserver.com/homepage.html',
'page' => {
'this' => 'mypage.html',
'next' => 'nextpage.html',
'prev' => 'prevpage.html',

},; };
template:: <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/home; page.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 Tem plate Toolkit will silently ignore (unless the DEBUG option is enabled).: my $vars = {
message => 'Hello World!',
_secret => "On the Internet, no-one knows you're a

dog",
thing => {
public => 123,

_private => 456,; '.hidden' => 789,
},
};
template:: [% message %] # outputs "Hello World!"
[% _secret %] # no output
[% thing.public %] # outputs "123"
[% thing._private %] # no output
[% thing..hidden %] # ERROR: unexpected token; (..)
To access a hash entry using a key stored in another vari able, prefix the key variable with '$' to have it interpo lated before use (see "Variable Interpolation").: [% pagename = 'next' %]
[% page.$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 intermedi ate 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
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 '=>'.: [% product = {
id => 'XYZ-2000',
desc => 'Bogon Generator',
price => 666,; }
%]
List References
Items in lists are also accessed by use of the dot opera tor.: my $vars = {
'people' => [ 'Tom', 'Dick', 'Larry' ],; };
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 = people %]
Hello [% person %]
[% END %]
output:: Hello Tom
Hello Dick
Hello Larry
Lists can be constructed in-situ using the regular anony mous list '[' ... ']' construct. Commas between items are optional.: [% cols = [ 'red', 'green', 'blue' ] %]; [% FOREACH c = cols %]
...; or:

[% FOREACH c = [ 'red', 'green', 'blue' ] %]
...

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] # z is [ 4, 5, 6, 7, 8 ]

%]

Subroutines

Template variables can contain references to Perl subrou
tines. When the variable is used, the Template Toolkit
will automatically call the subroutine, passing any addi
tional 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!',

@_) },

};

template:

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

cus Pocus!

Objects

Template variables can also contain references to Perl
objects. Methods are called using the dot operator to
specify the method against the object variable. Addi
tional 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'),

};

template:

[% FOREACH p = cgi.param %] # returns list of

param keys
[% p %] => [% cgi.param(p) %] # fetch each param

value
[% END %]

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) %]

Parameters and Return Values

Subroutines and methods will be passed any arguments spec
ified 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 auto
matically collected into a single hash array which is
passed by reference as the last parameter to the sub-rou
tine. 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 } || ' + ', @_);

}

template:

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

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 repre
sents. 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 refer
ence 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' ) },

};

template:

[% FOREACH i = items1 %]

...

[% END %]

[% FOREACH i = items2 %]

...

[% END %]

Error Handling

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' vari
able.

my $vars = {

barf => sub {
die "a sick error has occurred0;

},

};

template:

[% TRY %]

[% barf %] # calls sub which throws error

via die()

[% CATCH %]

[% error.info %] # outputs "a sick error has

occurred0

[% END %]

Error messages thrown via die() are converted to excep
tions of type 'undef'. Exceptions of user-defined types
can be thrown by calling die() with a reference to a Tem
plate::Exception object.

use Template::Exception;

...

my $vars = {

login => sub {

...
die Template::Exception->new('badpwd',
'password too

silly');

},

};

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 imple
ment the STOP and RETURN directives. Throwing an excep
tion as:

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

has the same effect as the directive:

[% STOP %]

Subroutines and methods can also raise errors by returning
a list or reference to a list containing the undefined
value (undef) followed by an exception object or error
message. This is supported for backwards compatibility
with version 1 but may be deprecated in some future
version.

my $vars = {

# currently equivalent
barf => sub {

die "I'm sorry Dave, I can't do that";

},
yack => sub {

return (undef, "I'm sorry Dave, I can't do

that");

},

};

Virtual Methods

The Template Toolkit implements a number of "virtual meth
ods" which can be applied to scalars, hashes or lists.
For example:

[% mylist = [ 'foo', 'bar', 'baz' ] %]
[% newlist = mylist.sort %]

Here 'mylist' is a regular reference to a list, and 'sort'
is a virtual method that returns a new list of the items
in sorted order. You can chain multiple virtual methods
together. For example:

[% mylist.sort.join(', ') %]

Here the 'join' virtual method is called to join the
sorted list into a single string, generating the following
output:

bar, baz, foo

See Template::Manual::VMethods for details of all the vir
tual methods available.

Variable Interpolation

The Template Toolkit uses '$' consistently to indicate
that a variable should be interpolated in position. Most
frequently, you see this in double-quoted strings:

[% fullname = "$honorific $firstname $surname" %]

Or embedded in plain text when the INTERPOLATE option is
set:

Dear $honorific $firstname $surname,

The same rules apply within directives. If a variable is
prefixed with a '$' then it is replaced with its value
before being used. The most common use is to retrieve an
element from a hash where the key is stored in a variable.

[% uid = 'abw' %]
[% userlist.$uid %] # same as

'userlist.abw'

Curly braces can be used to delimit interpolated variable
names where necessary.

[% userlist.${me.id}.name %]

Directives such as INCLUDE, PROCESS, etc., that accept a
template name as the first argument, will automatically
quote it for convenience.

[% INCLUDE foo/bar.txt %]

equivalent to:

[% INCLUDE "foo/bar.txt" %]

To INCLUDE a template whose name is stored in a variable,
simply prefix the variable name with '$' to have it inter
polated.

[% myfile = 'header' %]
[% INCLUDE $myfile %]

equivalent to:

[% INCLUDE header %]

Note also that a variable containing a reference to a Tem
plate::Document object can also be processed in this way.

my $vars = {

header => Template::Document->new({ ... }),

};

template:

[% INCLUDE $header %]

Local and Global Variables

Any simple variables that you create, or any changes you
make to existing variables, will only persist while the
template is being processed. The top-level variable hash
is copied before processing begins and any changes to
variables are made in this copy, leaving the original
intact. The same thing happens when you INCLUDE another
template. The current namespace hash is cloned to prevent
any variable changes made in the included template from
interfering with existing variables. The PROCESS option
bypasses the localisation step altogether making it
slightly faster, but requiring greater attention to the
possibility of side effects caused by creating or changing
any variables within the processed template.

[% BLOCK change_name %]

[% name = 'bar' %]

[% END %]

[% name = 'foo' %]
[% INCLUDE change_name %]
[% name %] # foo
[% PROCESS change_name %]
[% name %] # bar

Dotted compound variables behave slightly differently
because the localisation process is only skin deep. The
current variable namespace hash is copied, but no attempt
is made to perform a deep-copy of other structures within
it (hashes, arrays, objects, etc). A variable referencing
a hash, for example, will be copied to create a new refer
ence but which points to the same hash. Thus, the general
rule is that simple variables (undotted variables) are
localised, but existing complex structures (dotted vari
ables) are not.

[% BLOCK all_change %]

[% x = 20 %] # changes copy
[% y.z = 'zulu' %] # changes original

[% END %]

[% x = 10

y = { z => 'zebra' }

%]
[% INCLUDE all_change %]
[% x %] # still '10'
[% y.z %] # now 'zulu'

If you create a complex structure such as a hash or list
reference within a local template context then it will
cease to exist when the template is finished processing.

[% BLOCK new_stuff %]

[% # define a new 'y' hash array in local context

y = { z => 'zulu' }

%]

[% END %]

[% x = 10 %]
[% INCLUDE new_stuff %]
[% x %] # outputs '10'
[% y %] # nothing, y is unde

fined

Similarly, if you update an element of a compound variable
which doesn't already exists then a hash will be created automatically and deleted again at the end of the block.

[% BLOCK new_stuff %]

[% y.z = 'zulu' %]

[% END %]

However, if the hash does already exist then you will mod
ify the original with permanent effect. To avoid poten
tial confusion, it is recommended that you don't update
elements of complex variables from within blocks or tem
plates included by another.

If you want to create or update truly global variables
then you can use the 'global' namespace. This is a hash
array automatically created in the top-level namespace
which all templates, localised or otherwise see the same
reference to. Changes made to variables within this hash
are visible across all templates.

[% global.version = 123 %]

Compile Time Constant Folding

In addition to variables that get resolved each time a
template is processed, you can also define variables that
get resolved just once when the template is compiled.
This generally results in templates processing faster
because there is less work to be done.

To define compile-time constants, specify a CONSTANTS hash
as a constructor item as per VARIABLES. The CONSTANTS
hash can contain any kind of complex, nested, or dynamic
data structures, just like regular variables.

my $tt = Template->new({

CONSTANTS => {

version => 3.14,
release => 'skyrocket',
col => {
back => '#ffffff',
fore => '#000000',

},
myobj => My::Object->new(),
mysub => sub { ... },
joint => ', ',

},

});

Within a template, you access these variables using the
'constants' namespace prefix.

Version [% constants.version %] ([% constants.release

%])

Background: [% constants.col.back %]

When the template is compiled, these variable references
are replaced with the corresponding value. No further
variable lookup is then required when the template is pro
cessed.

You can call subroutines, object methods, and even virtual
methods on constant variables.

[% constants.mysub(10, 20) %]
[% constants.myobj(30, 40) %]
[% constants.col.keys.sort.join(', ') %]

One important proviso is that any arguments you pass to
subroutines or methods must also be literal values or com
pile time constants.

For example, these are both fine:

# literal argument
[% constants.col.keys.sort.join(', ') %]

# constant argument
[% constants.col.keys.sort.join(constants.joint) %]

But this next example will raise an error at parse time
because 'joint' is a runtime variable and cannot be deter
mined at compile time.

# ERROR: runtime variable argument!
[% constants.col.keys.sort.join(joint) %]

The CONSTANTS_NAMESPACE option can be used to provide a
different namespace prefix for constant variables. For
example:

my $tt = Template->new({

CONSTANTS => {

version => 3.14,
# ...etc...

},
CONSTANTS_NAMESPACE => 'const',

});

Constants would then be referenced in templates as:

[% const.version %]

Special Variables

A number of special variables are automatically defined by
the Template Toolkit.

template

The 'template' variable contains a reference to the
main template being processed, in the form of a Tem
plate::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.

component

The 'component' variable is like 'template' but always
contains a reference to the current, innermost tem
plate component being processed. In the main tem
plate, the 'template' and 'component' variable will
reference the same Template::Document object. In any
other template component called from the main tem
plate, 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(), "0;
'foo':: [% template.name %] # foo
[% component.name %] # foo
[% PROCESS footer %]
'footer':: [% template.name %] # foo
[% component.name %] # footer
loop: Within a FOREACH loop, the 'loop' variable references
the Template::Iterator object responsible for control
ling the loop.

[% FOREACH item = [ 'foo', 'bar', 'baz' ] -%]
[% "Items:0 IF loop.first -%]
[% loop.count %]/[% loop.size %]: [% item %]

[% END %]
error: 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 %]
content: 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 %]
<table border=1>
<tr>
<td>
[% content %]
</td>

</tr>
</table>
[% END %]
Compound Variables
Compound 'dotted' variables may contain any number of sep arate elements. Each element may evaluate to any of the permitted variable types and the processor will then cor rectly use this value to evaluate the rest of the vari able. Arguments may be passed to any of the intermediate elements.: [% myorg.people.sort('surname').first.fullname %]
Intermediate variables may be used and will behave entirely as expected.: [% sorted = myorg.people.sort('surname') %]
[% sorted.first.fullname %]
This simplified dotted notation has the benefit of hiding the implementation details of your data. For example, you could implement a data structure as a hash array one day and then change it to an object the next without requiring any change to the templates.

AUTHOR

Andy Wardley <abw@andywardley.com>

<http://www.andywardley.com/|http://www.andywardley.com/>

VERSION

Template Toolkit version 2.08, released on 30 July 2002.

COPYRIGHT

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

docs.sk