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Template::Manual::Variables - Template variables and code bindings
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 conflict with an existing or future reserved word. As of version 2.00, these are:
GET CALL SET DEFAULT INSERT INCLUDE PROCESS WRAPPER
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
[% article %]
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/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).
my $vars = {
message => 'Hello World!',
_secret => "On the Internet, no-one knows you're a dog",
thing => {
public => 123,
_private => 456,
'.hidden' => 789,
},
};
template:
[% message %] # outputs "Hello World!"
[% _secret %] # no output
[% thing.public %] # outputs "123"
[% thing._private %] # no output
[% thing..hidden %] # ERROR: unexpected token (..)
To access a hash entry using a key stored in another variable, prefix the key variable with '$' 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
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,
}
%]
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 anonymous 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 ]
%]
my $vars = {
wizard => sub { return join(' ', 'Abracadabra!', @_) },
};
template:
[% wizard %] # Abracadabra!
[% wizard('Hocus Pocus!') %] # Abracadabra! Hocus Pocus!
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) %]
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 } || ' + ', @_);
}
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 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' ) },
};
template:
[% FOREACH i = items1 %]
...
[% END %]
[% FOREACH i = items2 %]
...
[% END %]
my $vars = {
barf => sub {
die "a sick error has occurred\n";
},
};
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'. 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 {
...
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 implement the STOP and RETURN directives. Throwing an exception 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 $vars = {
# currently equivalent
barf => sub {
die "I'm sorry Dave, I can't do that";
},
yack => sub {
return (undef, "I'm sorry Dave, I can't do that");
},
};
[% mylist = [ 'foo', 'bar', 'baz' ] %]
[% newlist = mylist.sort %]
Here 'mylist' is a regular reference to a list, and 'sort' is a virtual method that returns a new list of the items in sorted order. You can chain multiple virtual methods together. For example:
[% mylist.sort.join(', ') %]
Here the 'join' virtual method is called to join the sorted list into a single string, generating the following output:
bar, baz, foo
See Template::Manual::VMethods for details of all the virtual methods available.
[% fullname = "$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 interpolated.
[% myfile = 'header' %]
[% INCLUDE $myfile %]
equivalent to:
[% INCLUDE header %]
Note also that a variable containing a reference to a Template::Document object can also be processed in this way.
my $vars = {
header => Template::Document->new({ ... }),
};
template:
[% INCLUDE $header %]
[% 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 reference but which points to the same hash. Thus, the general rule is that simple variables (undotted variables) are localised, but existing complex structures (dotted variables) 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 undefined
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 modify the original with permanent effect. To avoid potential confusion, it is recommended that you don't update elements of complex variables from within blocks or templates 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 %]
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 processed.
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 compile 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 determined 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 %]
Note that the 'template' variable always references the top-level template, even when processing other template components via INCLUDE, PROCESS, etc.
This example should demonstrate the difference:
$template->process('foo')
|| die $template->error(), "\n";
'foo':
[% template.name %] # foo
[% component.name %] # foo
[% PROCESS footer %]
'footer':
[% template.name %] # foo
[% component.name %] # footer
[% FOREACH item = [ 'foo', 'bar', 'baz' ] -%]
[% "Items:\n" IF loop.first -%]
[% loop.count %]/[% loop.size %]: [% item %]
[% END %]
[% TRY %]
...
[% CATCH %]
[% error %]
[% END %]
[% 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 %]
[% 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.
<http://www.andywardley.com/|http://www.andywardley.com/>
Copyright (C) 1996-2004 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.
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