Provided by: libtemplate-perl_2.22-0.1build2_amd64 bug

NAME

       Template::Tutorial::Web - Generating Web Content Using the Template Toolkit

Overview

       This tutorial document provides a introduction to the Template Toolkit and demonstrates
       some of the typical ways it may be used for generating web content. It covers the
       generation of static pages from templates using the tpage and ttree scripts and then goes
       on to show dynamic content generation using CGI scripts and Apache/mod_perl handlers.

       Various features of the Template Toolkit are introduced and described briefly and
       explained by use of example. For further information, see Template, Template::Manual and
       the various sections within it. e.g

           perldoc Template                    # Template.pm module usage
           perldoc Template::Manual            # index to manual
           perldoc Template::Manual::Config    # e.g. configuration options

       The documentation is also available in HTML format to read online, or download from the
       Template Toolkit web site:

           http://template-toolkit.org/docs/

Introduction

       The Template Toolkit is a set of Perl modules which collectively implement a template
       processing system.

       A template is a text document with special markup tags embedded in it.  By default, the
       Template Toolkit uses '"[%"' and '"%]"' to denote the start and end of a tag.  Here's an
       example:

           [% INCLUDE header %]

           People of [% planet %], your attention please.

           This is [% captain %] of the
           Galactic Hyperspace Planning Council.

           As you will no doubt be aware, the plans
           for development of the outlying regions
           of the Galaxy require the building of a
           hyperspatial express route through your
           star system, and regrettably your planet
           is one of those scheduled for destruction.

           The process will take slightly less than
           [% time %].

           Thank you.

           [% INCLUDE footer %]

       Tags can contain simple variables (like "planet" and "captain") and more complex
       directives that start with an upper case keyword (like "INCLUDE").  A directive is an
       instruction that tells the template processor to perform some action, like processing
       another template ("header" and "footer" in this example) and inserting the output into the
       current template. In fact, the simple variables we mentioned are actually "GET"
       directives, but the "GET" keyword is optional.

           People of [% planet %], your attention please.      # short form
           People of [% GET planet %], your attention please.  # long form

       Other directives include "SET" to set a variable value (the "SET" keyword is also
       optional), "FOREACH" to iterate through a list of values, and "IF", "UNLESS", "ELSIF" and
       "ELSE" to declare conditional blocks.

       The Template Toolkit processes all text files equally, regardless of what kind of content
       they contain.  So you can use TT to generate HTML, XML, CSS, Javascript, Perl, RTF, LaTeX,
       or any other text-based format.  In this tutorial, however, we'll be concentrating on
       generating HTML for web pages.

Generating Static Web Content

       Here's an example of a template used to generate an HTML document.

           [%  INCLUDE header
                 title = 'This is an HTML example';

               pages = [
                 { url   = 'http://foo.org'
                   title = 'The Foo Organisation'
                 }
                 { url   = 'http://bar.org'
                   title = 'The Bar Organisation'
                 }
               ]
           %]
              <h1>Some Interesting Links</h1>
              <ul>
           [%  FOREACH page IN pages %]
                <li><a href="[% page.url %]">[% page.title %]</a>
           [%  END %]
              </ul>

           [% INCLUDE footer %]

       This example shows how the "INCLUDE" directive is used to load and process separate
       '"header"' and '"footer"' template files, including the output in the current document.
       These files might look something like this:

       header:

           <html>
             <head>
               <title>[% title %]</title>
             </head>
             <body>

       footer:

               <div class="copyright">
                 &copy; Copyright 2007 Arthur Dent
               </div>
             </body>
           </html>

       The example also uses the "FOREACH" directive to iterate through the '"pages"' list to
       build a table of links. In this example, we have defined this list within the template to
       contain a number of hash references, each containing a '"url"' and '"title"' member. The
       "FOREACH" directive iterates through the list, aliasing '"page"' to each item (in this
       case, hash array references). The "[% page.url %]" and "[% page.title %]" directives then
       access the individual values in the hash ararys and insert them into the document.

   Using tpage
       Having created a template file we can now process it to generate some real output. The
       quickest and easiest way to do this is to use the tpage script. This is provided as part
       of the Template Toolkit and should be installed in your usual Perl bin directory.

       Assuming you saved your template file as example.html, you would run the command:

           $ tpage example.html

       This will process the template file, sending the output to "STDOUT" (i.e.  whizzing past
       you on the screen). You may want to redirect the output to a file but be careful not to
       specify the same name as the template file, or you'll overwrite it. You may want to use
       one prefix for your templates (e.g.  '".tt"') and another (e.g. '".html"') for the output
       files.

           $ tpage example.tt > example.html

       Or you can redirect the output to another directory. e.g.

           $ tpage templates/example.tt > html/example.html

       The output generated would look like this:

           <html>
             <head>
               <title>This is an HTML example</title>
             </head>
             <body>
               <h1>Some Interesting Links</h1>
               <ul>
                 <li><a href="http://foo.org">The Foo Organsiation</a>
                 <li><a href="http://bar.org">The Bar Organsiation</a>
               </ul>
               <div class="copyright">
                 &copy; Copyright 2007 Arthur Dent
               </div>
             </body>
           </html>

       The header and footer template files have been included (assuming you created them and
       they're in the current directory) and the link data has been built into an HTML list.

   Using ttree
       The tpage script gives you a simple and easy way to process a single template without
       having to write any Perl code. The <ttree:Template::Tools::ttree> script, also distributed
       as part of the Template Toolkit, provides a more flexible way to process a number of
       template documents in one go.

       The first time you run the script, it will ask you if it should create a configuration
       file (.ttreerc) in your home directory. Answer "y" to have it create the file.

       The <ttree:Template::Tools::ttree> documentation describes how you can change the location
       of this file and also explains the syntax and meaning of the various options in the file.
       Comments are written to the sample configuration file which should also help.

       In brief, the configuration file describes the directories in which template files are to
       be found ("src"), where the corresponding output should be written to ("dest"), and any
       other directories ("lib") that may contain template files that you plan to "INCLUDE" into
       your source documents. You can also specify processing options (such as "verbose" and
       "recurse") and provide regular expression to match files that you don't want to process
       ("ignore", "accept")> or should be copied instead of being processed as templates
       ("copy").

       An example .ttreerc file is shown here:

       $HOME/.ttreerc:

           verbose
           recurse

           # this is where I keep other ttree config files
           cfg = ~/.ttree

           src  = ~/websrc/src
           lib  = ~/websrc/lib
           dest = ~/public_html/test

           ignore = \b(CVS|RCS)\b
           ignore = ^#

       You can create many different configuration files and store them in the directory
       specified in the "cfg" option, shown above.  You then add the "-f filename" option to
       "ttree" to have it read that file.

       When you run the script, it compares all the files in the "src" directory (including those
       in sub-directories if the "recurse" option is set), with those in the "dest" directory.
       If the destination file doesn't exist or has an earlier modification time than the
       corresponding source file, then the source will be processed with the output written to
       the destination file.  The "-a" option forces all files to be processed, regardless of
       modification times.

       The script doesn't process any of the files in the "lib" directory, but it does add it to
       the "INCLUDE_PATH" for the template processor so that it can locate these files via an
       "INCLUDE", "PROCESS" or "WRAPPER" directive.  Thus, the "lib" directory is an excellent
       place to keep template elements such as header, footers, etc., that aren't complete
       documents in their own right.

       You can also specify various Template Toolkit options from the configuration file. Consult
       the ttree documentation and help summary ("ttree -h") for full details. e.g.

       $HOME/.ttreerc:

           pre_process = config
           interpolate
           post_chomp

       The "pre_process" option allows you to specify a template file which should be processed
       before each file.  Unsurprisingly, there's also a "post_process" option to add a template
       after each file.  In the fragment above, we have specified that the "config" template
       should be used as a prefix template.  We can create this file in the "lib" directory and
       use it to define some common variables, including those web page links we defined earlier
       and might want to re-use in other templates.  We could also include an HTML header, title,
       or menu bar in this file which would then be prepended to each and every template file,
       but for now we'll keep all that in a separate "header" file.

       $lib/config:

           [% root     = '~/abw'
              home     = "$root/index.html"
              images   = "$root/images"
              email    = 'abw@wardley.org'
              graphics = 1
              webpages = [
                { url => 'http://foo.org', title => 'The Foo Organsiation' }
                { url => 'http://bar.org', title => 'The Bar Organsiation' }
              ]
           %]

       Assuming you've created or copied the "header" and "footer" files from the earlier example
       into your "lib" directory, you can now start to create web pages like the following in
       your "src" directory and process them with "ttree".

       $src/newpage.html:

           [% INCLUDE header
              title = 'Another Template Toolkit Test Page'
           %]

               <a href="[% home %]">Home</a>
               <a href="mailto:[% email %]">Email</a>

           [% IF graphics %]
               <img src="[% images %]/logo.gif" align=right width=60 height=40>
           [% END %]

           [% INCLUDE footer %]

       Here we've shown how pre-defined variables can be used as flags to enable certain feature
       (e.g. "graphics") and to specify common items such as an email address and URL's for the
       home page, images directory and so on.  This approach allows you to define these values
       once so that they're consistent across all pages and can easily be changed to new values.

       When you run ttree, you should see output similar to the following (assuming you have the
       verbose flag set).

           ttree 2.9 (Template Toolkit version 2.20)

                Source: /home/abw/websrc/src
           Destination: /home/abw/public_html/test
          Include Path: [ /home/abw/websrc/lib ]
                Ignore: [ \b(CVS|RCS)\b, ^# ]
                  Copy: [  ]
                Accept: [ * ]

           + newpage.html

       The "+" in front of the "newpage.html" filename shows that the file was processed, with
       the output being written to the destination directory. If you run the same command again,
       you'll see the following line displayed instead showing a "-" and giving a reason why the
       file wasn't processed.

           - newpage.html                     (not modified)

       It has detected a "newpage.html" in the destination directory which is more recent than
       that in the source directory and so hasn't bothered to waste time re-processing it.  To
       force all files to be processed, use the "-a" option.  You can also specify one or more
       filenames as command line arguments to "ttree":

           tpage newpage.html

       This is what the destination page looks like.

       $dest/newpage.html:

           <html>
             <head>
               <title>Another Template Toolkit Test Page</title>
             </head>
             <body>

               <a href="~/abw/index.html">Home</a>
               <a href="mailto:abw@wardley.org">Email me</a>
               <img src="~/abw/images/logo.gif" align=right width=60 height=40>

               <div class="copyright">
                 &copy; Copyright 2007 Arthur Dent
               </div>
             </body>
           </html>

       You can add as many documents as you like to the "src" directory and "ttree" will apply
       the same process to them all.  In this way, it is possible to build an entire tree of
       static content for a web site with a single command.  The added benefit is that you can be
       assured of consistency in links, header style, or whatever else you choose to implement in
       terms of common templates elements or variables.

Dynamic Content Generation Via CGI Script

       The Template module provides a simple front-end to the Template Toolkit for use in CGI
       scripts and Apache/mod_perl handlers. Simply "use" the Template module, create an object
       instance with the new() method and then call the process() method on the object, passing
       the name of the template file as a parameter. The second parameter passed is a reference
       to a hash array of variables that we want made available to the template:

           #!/usr/bin/perl
           use strict;
           use warnings;
           use Template;

           my $file = 'src/greeting.html';
           my $vars = {
              message  => "Hello World\n"
           };

           my $template = Template->new();

           $template->process($file, $vars)
               || die "Template process failed: ", $template->error(), "\n";

       So that our scripts will work with the same template files as our earlier examples, we'll
       can add some configuration options to the constructor to tell it about our environment:

           my $template->new({
               # where to find template files
               INCLUDE_PATH => ['/home/abw/websrc/src', '/home/abw/websrc/lib'],
               # pre-process lib/config to define any extra values
               PRE_PROCESS  => 'config',
           });

       Note that here we specify the "config" file as a "PRE_PROCESS" option.  This means that
       the templates we process can use the same global variables defined earlier for our static
       pages.  We don't have to replicate their definitions in this script.  However, we can
       supply additional data and functionality specific to this script via the hash of variables
       that we pass to the "process()" method.

       These entries in this hash may contain simple text or other values, references to lists,
       others hashes, sub-routines or objects.  The Template Toolkit will automatically apply the
       correct procedure to access these different types when you use the variables in a
       template.

       Here's a more detailed example to look over.  Amongst the different template variables we
       define in $vars, we create a reference to a CGI object and a "get_user_projects()" sub-
       routine.

           #!/usr/bin/perl
           use strict;
           use warnings;
           use Template;
           use CGI;

           $| = 1;
           print "Content-type: text/html\n\n";

           my $file = 'userinfo.html';
           my $vars = {
               'version'  => 3.14,
               'days'     => [ qw( mon tue wed thu fri sat sun ) ],
               'worklist' => \&get_user_projects,
               'cgi'      => CGI->new(),
               'me'       => {
                   'id'     => 'abw',
                   'name'   => 'Andy Wardley',
               },
           };

           sub get_user_projects {
               my $user = shift;
               my @projects = ...   # do something to retrieve data
               return \@projects;
           }

           my $template = Template->new({
               INCLUDE_PATH => '/home/abw/websrc/src:/home/abw/websrc/lib',
               PRE_PROCESS  => 'config',
           });

           $template->process($file, $vars)
               || die $template->error();

       Here's a sample template file that we might create to build the output for this script.

       $src/userinfo.html:

           [% INCLUDE header
              title = 'Template Toolkit CGI Test'
           %]

           <a href="mailto:[% email %]">Email [% me.name %]</a>

           <p>This is version [% version %]</p>

           <h3>Projects</h3>
           <ul>
           [% FOREACH project IN worklist(me.id) %]
              <li> <a href="[% project.url %]">[% project.name %]</a>
           [% END %]
           </ul>

           [% INCLUDE footer %]

       This example shows how we've separated the Perl implementation (code) from the
       presentation (HTML). This not only makes them easier to maintain in isolation, but also
       allows the re-use of existing template elements such as headers and footers, etc. By using
       template to create the output of your CGI scripts, you can give them the same consistency
       as your static pages built via ttree or other means.

       Furthermore, we can modify our script so that it processes any one of a number of
       different templates based on some condition.  A CGI script to maintain a user database,
       for example, might process one template to provide an empty form for new users, the same
       form with some default values set for updating an existing user record, a third template
       for listing all users in the system, and so on.  You can use any Perl functionality you
       care to write to implement the logic of your application and then choose one or other
       template to generate the desired output for the application state.

Dynamic Content Generation Via Apache/Mod_Perl Handler

       NOTE: the Apache::Template module is available from CPAN and provides a simple and easy to
       use Apache/mod_perl interface to the Template Toolkit.  Although basic, it implements
       most, if not all of what is described below, and it avoids the need to write your own
       handler. However, in many cases, you'll want to write your own handler to customise
       processing for your own need, and this section will show you how to get started.

       The Template module can be used from an Apache/mod_perl handler. Here's an example of a
       typical Apache httpd.conf file:

           PerlModule CGI;
           PerlModule Template
           PerlModule MyOrg::Apache::User

           PerlSetVar websrc_root   /home/abw/websrc

           <Location /user/bin>
               SetHandler     perl-script
               PerlHandler    MyOrg::Apache::User
           </Location>

       This defines a location called "/user/bin" to which all requests will be forwarded to the
       "handler()" method of the "MyOrg::Apache::User" module.  That module might look something
       like this:

           package MyOrg::Apache::User;

           use strict;
           use vars qw( $VERSION );
           use Apache::Constants qw( :common );
           use Template qw( :template );
           use CGI;

           $VERSION = 1.59;

           sub handler {
               my $r = shift;

               my $websrc = $r->dir_config('websrc_root')
                   or return fail($r, SERVER_ERROR,
                                  "'websrc_root' not specified");

               my $template = Template->new({
                   INCLUDE_PATH  => "$websrc/src/user:$websrc/lib",
                   PRE_PROCESS   => 'config',
                   OUTPUT        => $r,     # direct output to Apache request
               });

               my $params = {
                   uri     => $r->uri,
                   cgi     => CGI->new,
               };

               # use the path_info to determine which template file to process
               my $file = $r->path_info;
               $file =~ s[^/][];

               $r->content_type('text/html');
               $r->send_http_header;

               $template->process($file, $params)
                   || return fail($r, SERVER_ERROR, $template->error());

               return OK;
           }

           sub fail {
               my ($r, $status, $message) = @_;
               $r->log_reason($message, $r->filename);
               return $status;
           }

       The handler accepts the request and uses it to determine the "websrc_root" value from the
       config file.  This is then used to define an "INCLUDE_PATH" for a new Template object.
       The URI is extracted from the request and a CGI object is created.  These are both defined
       as template variables.

       The name of the template file itself is taken from the "PATH_INFO" element of the request.
       In this case, it would comprise the part of the URL coming after "/user/bin",  e.g for
       "/user/bin/edit", the template file would be "edit" located in "$websrc/src/user".  The
       headers are sent and the template file is processed.  All output is sent directly to the
       "print()" method of the Apache request object.

Using Plugins to Extend Functionality

       As we've already shown, it is possible to bind Perl data and functions to template
       variables when creating dynamic content via a CGI script or Apache/mod_perl process.  The
       Template Toolkit also supports a plugin interface which allows you define such additional
       data and/or functionality in a separate module and then load and use it as required with
       the "USE" directive.

       The main benefit to this approach is that you can load the extension into any template
       document, even those that are processed "statically" by "tpage" or "ttree".  You don't
       need to write a Perl wrapper to explicitly load the module and make it available via the
       stash.

       Let's demonstrate this principle using the "DBI" plugin written by Simon Matthews
       (available from CPAN). You can create this template in your "src" directory and process it
       using "ttree" to see the results. Of course, this example relies on the existence of the
       appropriate SQL database but you should be able to adapt it to your own resources, or at
       least use it as a demonstrative example of what's possible.

           [% INCLUDE header
                title = 'User Info'
           %]

           [% USE DBI('dbi:mSQL:mydbname') %]

           <table border=0 width="100%">
             <tr>
               <th>User ID</th>
               <th>Name</th>
               <th>Email</th>
             </tr>
           [% FOREACH user IN DBI.query('SELECT * FROM user ORDER BY id') %]
             <tr>
               <td>[% user.id %]</td>
               <td>[% user.name %]</td>
               <td>[% user.email %]</td>
             </tr>
           [% END %]
           </table>

           [% INCLUDE footer %]

       A plugin is simply a Perl module in a known location and conforming to a known standard
       such that the Template Toolkit can find and load it automatically.  You can create your
       own plugin by inheriting from the Template::Plugin module.

       Here's an example which defines some data items ("foo" and "people") and also an object
       method ("bar").  We'll call the plugin "FooBar" for want of a better name and create it in
       the "MyOrg::Template::Plugin::FooBar" package.  We've added a "MyOrg" to the regular
       "Template::Plugin::*" package to avoid any conflict with existing plugins.

           package MyOrg::Template::Plugin::FooBar;
           use base 'Template::Plugin'
           our $VERSION = 1.23;

           sub new {
               my ($class, $context, @params) = @_;

               bless {
                   _CONTEXT => $context,
                   foo      => 25,
                   people   => [ 'tom', 'dick', 'harry' ],
               }, $class;
           }

           sub bar {
               my ($self, @params) = @_;
               # ...do something...
               return $some_value;
           }

       The plugin constructor "new()" receives the class name as the first parameter, as is usual
       in Perl, followed by a reference to something called a Template::Context object. You don't
       need to worry too much about this at the moment, other than to know that it's the main
       processing object for the Template Toolkit. It provides access to the functionality of the
       processor and some plugins may need to communicate with it. We don't at this stage, but
       we'll save the reference anyway in the "_CONTEXT" member. The leading underscore is a
       convention which indicates that this item is private and the Template Toolkit won't
       attempt to access this member. The other members defined, "foo" and "people" are regular
       data items which will be made available to templates using this plugin. Following the
       context reference are passed any additional parameters specified with the USE directive,
       such as the data source parameter, "dbi:mSQL:mydbname", that we used in the earlier DBI
       example.

       If you don't or can't install it to the regular place for your Perl modules (perhaps
       because you don't have the required privileges) then you can set the PERL5LIB environment
       variable to specify another location.  If you're using "ttree" then you can add the
       following line to your configuration file instead.

       $HOME/.ttreerc:

           perl5lib = /path/to/modules

       One further configuration item must be added to inform the toolkit of the new package name
       we have adopted for our plugins:

       $HOME/.ttreerc:

           plugin_base = 'MyOrg::Template::Plugin'

       If you're writing Perl code to control the Template modules directly, then this value can
       be passed as a configuration parameter when you create the module.

           use Template;

           my $template = Template->new({
               PLUGIN_BASE => 'MyOrg::Template::Plugin'
           });

       Now we can create a template which uses this plugin:

           [% INCLUDE header
              title = 'FooBar Plugin Test'
           %]

           [% USE FooBar %]

           Some values available from this plugin:
             [% FooBar.foo %] [% FooBar.bar %]

           The users defined in the 'people' list:
           [% FOREACH uid = FooBar.people %]
             * [% uid %]
           [% END %]

           [% INCLUDE footer %]

       The "foo", "bar", and "people" items of the FooBar plugin are automatically resolved to
       the appropriate data items or method calls on the underlying object.

       Using this approach, it is possible to create application functionality in a single module
       which can then be loaded and used on demand in any template.  The simple interface between
       template directives and plugin objects allows complex, dynamic content to be built from a
       few simple template documents without knowing anything about the underlying
       implementation.

AUTHOR

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

COPYRIGHT

       Copyright (C) 1996-2007 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.