phpman > perldoc > Template::Manual::Variables

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

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 template:

        This is version [% version %] ([% release %]).
        Serial number: [% serial_no %]

    Generated 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 data:

        my $vars = {
            article => 'The Third Shoe',
            person  => {
                id    => 314,
                name  => 'Mr. Blue',
                email => 'blue AT nowhere.org',
            },
            primes  => [ 2, 3, 5, 7, 11, 13 ],
            wizard  => sub { return join(' ', 'Abracadabra!', @_) },
            cgi     => CGI->new('mode=submit&debug=1'),
        };

    Example 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') %]

    Generated output:

        The Third Shoe

        314: Mr. Blue <blue AT 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 namespace 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.

    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,
           }
        %]

  List References
    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 ]
        %]

  Subroutines
    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!

  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. 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) %]

  Passing Parameters and Returning Values
    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 %]

  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" 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 %]

Virtual Methods
    The Template Toolkit implements a number of "virtual methods" 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 virtual 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' %]
        [% users.$uid %]         # same as 'userlist.abw'

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

        [% users.${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 %]

    The above example is 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 %]

    This is 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({ ... }),
        };

    Example 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 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 %]

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 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 %]

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 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.

  component
    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' ]

  loop
    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 %]

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

Compound Variables
    Compound 'dotted' variables may contain any number of separate elements. Each element may
    evaluate to any of the permitted variable types and the processor will then correctly use this
    value to evaluate the rest of the variable. 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.