Template(3)

NAME
Template - Front-end module to the Template Toolkit

SYNOPSIS
    use Template;

    # some useful options (see below for full list)
    my $config = {
        INCLUDE_PATH => '/search/path',  # or list ref
        INTERPOLATE  => 1,               # expand "$var" in plain text
        POST_CHOMP   => 1,               # cleanup whitespace
        PRE_PROCESS  => 'header',        # prefix each template
        EVAL_PERL    => 1,               # evaluate Perl code blocks
    };

    # create Template object
    my $template = Template->new($config);

    # define template variables for replacement
    my $vars = {
        var1  => $value,
        var2  => \%hash,
        var3  => \@list,
        var4  => \&code,
        var5  => $object,
    };

    # specify input filename, or file handle, text reference, etc.
    my $input = 'myfile.html';

    # process input template, substituting variables
    $template->process($input, $vars)
        || die $template->error();

DESCRIPTION
This documentation describes the Template module which is the direct Perl interface into the Template Toolkit. It covers the use of the module and gives a brief summary of configuration options and template directives. Please see Template::Manual for the complete reference manual which goes into much greater depth about the features and use of the Template Toolkit. The Template::Tutorial is also available as an introductory guide to using the Template Toolkit.

METHODS

  new(\%config)
The "new()" constructor method (implemented by the Template::Base base class) instantiates a new "Template" object. A reference to a hash array of configuration items may be passed as a parameter.

    my $tt = Template->new({
        INCLUDE_PATH => '/usr/local/templates',
        EVAL_PERL    => 1,
    }) || die $Template::ERROR, "\n";

A reference to a new "Template" object is returned, or undef on error. In the latter case, the error message can be retrieved by calling error() as a class method or by examining the $Template::ERROR package variable directly.

    my $tt = Template->new(\%config)
        || die Template->error(), "\n";

    my $tt = Template->new(\%config)
        || die $Template::ERROR, "\n";

For convenience, configuration items may also be specified as a list of items instead of a hash array reference. These are automatically folded into a hash array by the constructor.

    my $tt = Template->new(INCLUDE_PATH => '/tmp', POST_CHOMP => 1)
        || die $Template::ERROR, "\n";

  process($template, \%vars, $output, %options)
The "process()" method is called to process a template. The first parameter indicates the input template as one of:

•   a filename relative to "INCLUDE_PATH", if defined

•   a reference to a text string containing the template text

•   a file handle reference (e.g. "IO::Handle" or sub-class) or "GLOB" (e.g. "\*STDIN"), from which the template can be read.

A reference to a hash array may be passed as the second parameter, containing definitions of template variables.

    # filename
    $tt->process('welcome.tt2')
        || die $tt->error(), "\n";

    # text reference
    $text = "[% INCLUDE header %]\nHello world!\n[% INCLUDE footer %]";
    $tt->process(\$text)
        || die $tt->error(), "\n";

    # file handle (GLOB)
    $tt->process(\*DATA)
        || die $tt->error(), "\n";

    __END__
    [% INCLUDE header %]
    This is a template defined in the __END__ section which is
    accessible via the DATA "file handle".
    [% INCLUDE footer %]

By default, the processed template output is printed to "STDOUT". The "process()" method then returns 1 to indicate success. A third parameter may be passed to the "process()" method to specify a different output location. This value may be one of:

•   a plain string indicating a filename which will be opened (relative to "OUTPUT_PATH", if defined) and the output written to

•   a file GLOB opened ready for output

•   a reference to a scalar (e.g. a text string) to which output/error is appended

•   a reference to a subroutine which is called, passing the output as a parameter

•   any object reference which implements a "print()" method (e.g. "IO::Handle", "Apache::Request", etc.) which will be called, passing the generated output as a parameter.

Examples:

    # output filename
    $tt->process('welcome.tt2', $vars, 'welcome.html')
        || die $tt->error(), "\n";

    # reference to output subroutine
    sub myout {
        my $output = shift;
        ...
    }
    $tt->process('welcome.tt2', $vars, \&myout)
        || die $tt->error(), "\n";

    # reference to output text string
    my $output = '';
    $tt->process('welcome.tt2', $vars, \$output)
        || die $tt->error(), "\n";

    print "output: $output\n";

In an Apache/mod_perl handler:

    sub handler {
        my $req = shift;

        # ...your code here...

        # direct output to Apache::Request via $req->print($output)
        $tt->process($file, $vars, $req) || do {
            $req->log_reason($tt->error());
            return SERVER_ERROR;
        };
        return OK;
    }

After the optional third output argument can come an optional reference to a hash or a list of "(name, value)" pairs providing further options for the output. The only option currently supported is "binmode" which, when set to any true value will ensure that files created (but not any existing file handles passed) will be set to binary mode.

    # either: hash reference of options
    $tt->process($infile, $vars, $outfile, { binmode => 1 })
        || die $tt->error(), "\n";

    # or: list of name, value pairs
    $tt->process($infile, $vars, $outfile, binmode => 1)
        || die $tt->error(), "\n";

Alternately, the "binmode" argument can specify a particular IO layer such as ":utf8".

    $tt->process($infile, $vars, $outfile, binmode => ':utf8')
        || die $tt->error(), "\n";

The "OUTPUT" configuration item can be used to specify a default output location other than "\*STDOUT". The "OUTPUT_PATH" specifies a directory which should be prefixed to all output locations specified as filenames.

    my $tt = Template->new({
        OUTPUT      => sub { ... },       # default
        OUTPUT_PATH => '/tmp',
    ...
    }) || die Template->error(), "\n";

    # use default OUTPUT (sub is called)
    $tt->process('welcome.tt2', $vars)
        || die $tt->error(), "\n";

    # write file to '/tmp/welcome.html'
    $tt->process('welcome.tt2', $vars, 'welcome.html')
        || die $tt->error(), "\n";

The "process()" method returns 1 on success or "undef" on error. The error message generated in the latter case can be retrieved by calling the error() method. See also "CONFIGURATION SUMMARY" which describes how error handling may be further customised.

  error()
When called as a class method, it returns the value of the $ERROR package variable. Thus, the following are equivalent.

    my $tt = Template->new()
        || die Template->error(), "\n";

    my $tt = Template->new()
        || die $Template::ERROR, "\n";

When called as an object method, it returns the value of the internal "_ERROR" variable, as set by an error condition in a previous call to process().

    $tt->process('welcome.tt2')
        || die $tt->error(), "\n";

Errors are represented in the Template Toolkit by objects of the Template::Exception class. If the process() method returns a false value then the "error()" method can be called to return an object of this class. The type() and info() methods can called on the object to retrieve the error type and information string, respectively. The as_string() method can be called to return a string of the form "$type - $info". This method is also overloaded onto the stringification operator allowing the object reference itself to be printed to return the formatted error string.

    $tt->process('somefile') || do {
        my $error = $tt->error();
        print "error type: ", $error->type(), "\n";
        print "error info: ", $error->info(), "\n";
        print $error, "\n";
    };

  service()
The "Template" module delegates most of the effort of processing templates to an underlying Template::Service object. This method returns a reference to that object.

  context()
The Template::Service module uses a core Template::Context object for runtime processing of templates. This method returns a reference to that object and is equivalent to "$template->service->context()".

  template($name)
This method is a simple wrapper around the Template::Context method of the same name. It returns a compiled template for the source provided as an argument.

CONFIGURATION SUMMARY
The following list gives a short summary of each Template Toolkit configuration option. See Template::Manual::Config for full details.

  Template Style and Parsing Options
ENCODING

Specifies the character encoding.

START_TAG, END_TAG

Define tokens that indicate start and end of directives (default: '"[%"' and '"%]"').

TAG_STYLE

Set "START_TAG" and "END_TAG" according to a pre-defined style (default: '"template"', as above).

PRE_CHOMP, POST_CHOMP

Removes whitespace before/after directives (default: 0/0).

TRIM

Remove leading and trailing whitespace from template output (default: 0).

INTERPOLATE

Interpolate variables embedded like $this or "${this}" (default: 0).

ANYCASE

Allow directive keywords in lower case (default: 0 - UPPER only).

  Template Files and Blocks
INCLUDE_PATH

One or more directories to search for templates.

DELIMITER

Delimiter for separating paths in "INCLUDE_PATH" (default: '":"').

ABSOLUTE

Allow absolute file names, e.g. "/foo/bar.html" (default: 0).

RELATIVE

Allow relative filenames, e.g. "../foo/bar.html" (default: 0).

DEFAULT

Default template to use when another not found.

BLOCKS

Hash array pre-defining template blocks.

AUTO_RESET

Enabled by default causing "BLOCK" definitions to be reset each time a template is processed. Disable to allow "BLOCK" definitions to persist.

RECURSION

Flag to permit recursion into templates (default: 0).

  Template Variables
VARIABLES

Hash array of variables and values to pre-define in the stash.

  Runtime Processing Options
EVAL_PERL

Flag to indicate if "PERL"/"RAWPERL" blocks should be processed (default: 0).

PRE_PROCESS, POST_PROCESS

Name of template(s) to process before/after main template.

PROCESS

Name of template(s) to process instead of main template.

ERROR

Name of error template or reference to hash array mapping error types to templates.

OUTPUT

Default output location or handler.

OUTPUT_PATH

Directory into which output files can be written.

DEBUG

Enable debugging messages.

  Caching and Compiling Options
CACHE_SIZE

Maximum number of compiled templates to cache in memory (default: undef - cache all)

COMPILE_EXT

Filename extension for compiled template files (default: undef - don't compile).

COMPILE_DIR

Root of directory in which compiled template files should be written (default: undef - don't compile).

  Plugins and Filters
PLUGINS

Reference to a hash array mapping plugin names to Perl packages.

PLUGIN_BASE

One or more base classes under which plugins may be found.

LOAD_PERL

Flag to indicate regular Perl modules should be loaded if a named plugin can't be found (default: 0).

FILTERS

Hash array mapping filter names to filter subroutines or factories.

  Customisation and Extension
LOAD_TEMPLATES

List of template providers.

LOAD_PLUGINS

List of plugin providers.

LOAD_FILTERS

List of filter providers.

TOLERANT

Set providers to tolerate errors as declinations (default: 0).

SERVICE

Reference to a custom service object (default: Template::Service).

CONTEXT

Reference to a custom context object (default: Template::Context).

STASH

Reference to a custom stash object (default: Template::Stash).

PARSER

Reference to a custom parser object (default: Template::Parser).

GRAMMAR

Reference to a custom grammar object (default: Template::Grammar).

DIRECTIVE SUMMARY
The following list gives a short summary of each Template Toolkit directive. See Template::Manual::Directives for full details.

  GET
Evaluate and print a variable or value.

    [%   GET variable %]    # 'GET' keyword is optional
    [%       variable %]
    [%       hash.key %]
    [%         list.n %]
    [%     code(args) %]
    [% obj.meth(args) %]
    [%  "value: $var" %]

  CALL
As per GET but without printing result (e.g. call code)

    [%  CALL variable %]

  SET
Assign a values to variables.

    [% SET variable = value %]    # 'SET' also optional
    [%     variable = other_variable
           variable = 'literal text @ $100'
           variable = "interpolated text: $var"
           list     = [ val, val, val, val, ... ]
           list     = [ val..val ]
           hash     = { var => val, var => val, ... }
    %]

  DEFAULT
Like SET, but variables are only set if currently unset (i.e. have no true value).

    [% DEFAULT variable = value %]

  INSERT
Insert a file without any processing performed on the contents.

    [% INSERT legalese.txt %]

  PROCESS
Process another template file or block and insert the generated output. Any template BLOCKs or variables defined or updated in the "PROCESS"ed template will thereafter be defined in the calling template.

    [% PROCESS template %]
    [% PROCESS template  var = val, ... %]

  INCLUDE
Similar to "PROCESS", but using a local copy of the current variables. Any template "BLOCK"s or variables defined in the "INCLUDE"d template remain local to it.

    [% INCLUDE template %]
    [% INCLUDE template  var = val, ... %]

  WRAPPER
The content between the "WRAPPER" and corresponding "END" directives is first evaluated, with the output generated being stored in the "content" variable. The named template is then process as per "INCLUDE".

    [% WRAPPER layout %]
       Some template markup [% blah %]...
    [% END %]

A simple layout template might look something like this:

    Your header here...
    [% content %]
    Your footer here...

  BLOCK
Define a named template block for INCLUDE, PROCESS and WRAPPER to use.

    [% BLOCK hello %]
       Hello World
    [% END %]

    [% INCLUDE hello %]

  FOREACH
Repeat the enclosed "FOREACH" ... "END" block for each value in the list.

    [% FOREACH variable IN [ val, val, val ] %]    # either
    [% FOREACH variable IN list %]                 # or
       The variable is set to [% variable %]
    [% END %]

  WHILE
The block enclosed between "WHILE" and "END" block is processed while the specified condition is true.

    [% WHILE condition %]
       content
    [% END %]

  IF / UNLESS / ELSIF / ELSE
The enclosed block is processed if the condition is true / false.

    [% IF condition %]
       content
    [% ELSIF condition %]
     content
    [% ELSE %]
     content
    [% END %]

    [% UNLESS condition %]
       content
    [% # ELSIF/ELSE as per IF, above %]
       content
    [% END %]

  SWITCH / CASE
Multi-way switch/case statement.

    [% SWITCH variable %]
    [%   CASE val1 %]
           content
    [%   CASE [ val2, val3 ] %]
           content
    [%   CASE %]         # or [% CASE DEFAULT %]
           content
    [% END %]

  MACRO
Define a named macro.

    [% MACRO name <directive> %]
    [% MACRO name(arg1, arg2) <directive> %]
    ...
    [% name %]
    [% name(val1, val2) %]

  FILTER
Process enclosed "FILTER" ... "END" block then pipe through a filter.

    [% FILTER name %]                       # either
    [% FILTER name( params ) %]             # or
    [% FILTER alias = name( params ) %]     # or
       content
    [% END %]

  USE
Load a plugin module (see "Template::<Manual::Plugins"), or any regular Perl module when the "LOAD_PERL" option is set.

    [% USE name %]                      # either
    [% USE name( params ) %]            # or
    [% USE var = name( params ) %]      # or
    ...
    [% name.method %]
    [% var.method %]

  PERL / RAWPERL
Evaluate enclosed blocks as Perl code (requires the "EVAL_PERL" option to be set).

    [% PERL %]
     # perl code goes here
     $stash->set('foo', 10);
     print "set 'foo' to ", $stash->get('foo'), "\n";
     print $context->include('footer', { var => $val });
    [% END %]

    [% RAWPERL %]
       # raw perl code goes here, no magic but fast.
       $output .= 'some output';
    [% END %]

  TRY / THROW / CATCH / FINAL
Exception handling.

    [% TRY %]
     content
       [% THROW type info %]
    [% CATCH type %]
     catch content
       [% error.type %] [% error.info %]
    [% CATCH %] # or [% CATCH DEFAULT %]
     content
    [% FINAL %]
       this block is always processed
    [% END %]

  NEXT
Jump straight to the next item in a "FOREACH" or "WHILE" loop.

    [% NEXT %]

  LAST
Break out of "FOREACH" or "WHILE" loop.

    [% LAST %]

  RETURN
Stop processing current template and return to including templates.

    [% RETURN %]

  STOP
Stop processing all templates and return to caller.

    [% STOP %]

  TAGS
Define new tag style or characters (default: "[%" "%]").

    [% TAGS html %]
    [% TAGS <!-- --> %]

  COMMENTS
Ignored and deleted.

    [% # this is a comment to the end of line
       foo = 'bar'
    %]

    [%# placing the '#' immediately inside the directive
        tag comments out the entire directive
    %]

SOURCE CODE REPOSITORY
The source code for the Template Toolkit is held in a public git repository on Github: <https://github.com/abw/Template2>

AUTHOR
Andy Wardley <abw@wardley.org> <http://wardley.org/>

VERSION
Template Toolkit version 3.010, released on July 13 2020.

SUPPORT
The Template Toolkit mailing list provides a forum for discussing issues relating to the use and abuse of the Template Toolkit. There are a number of knowledgeable and helpful individuals who frequent the list (including the author) who can often offer help or suggestions. Please respect their time and patience by checking the documentation and/or mailing list archives before asking questions that may already have been answered.

To subscribe to the mailing list, send an email to:

    template-toolkit+subscribe@groups.io

You can also use the web interface:

    https://groups.io/g/template-toolkit

For information about commercial support and consultancy for the Template Toolkit, please contact the author.

COPYRIGHT
Copyright (C) 1996-2020 Andy Wardley. All Rights Reserved.

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