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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)