TemplateTutorialWeb

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[root@slashcode man3]# man Template::Tutorial::Web | cat Template::Tutorial::WeUser Contributed Perl DocumentTemplate::Tutorial::Web(3)


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">
                 © 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 arrays 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">
                 © 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">
                 © 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.



perl v5.10.1                      2013-07-23        Template::Tutorial::Web(3)