📄 template.pm
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package HTML::Template;
$HTML::Template::VERSION = '2.8';
=head1 NAME
HTML::Template - Perl module to use HTML Templates from CGI scripts
=head1 SYNOPSIS
First you make a template - this is just a normal HTML file with a few
extra tags, the simplest being <TMPL_VAR>
For example, test.tmpl:
<html>
<head><title>Test Template</title>
<body>
My Home Directory is <TMPL_VAR NAME=HOME>
<p>
My Path is set to <TMPL_VAR NAME=PATH>
</body>
</html>
Now create a small CGI program:
#!/usr/bin/perl -w
use HTML::Template;
# open the html template
my $template = HTML::Template->new(filename => 'test.tmpl');
# fill in some parameters
$template->param(HOME => $ENV{HOME});
$template->param(PATH => $ENV{PATH});
# send the obligatory Content-Type and print the template output
print "Content-Type: text/html\n\n", $template->output;
If all is well in the universe this should show something like this in
your browser when visiting the CGI:
My Home Directory is /home/some/directory
My Path is set to /bin;/usr/bin
=head1 DESCRIPTION
This module attempts to make using HTML templates simple and natural.
It extends standard HTML with a few new HTML-esque tags - <TMPL_VAR>,
<TMPL_LOOP>, <TMPL_INCLUDE>, <TMPL_IF>, <TMPL_ELSE> and <TMPL_UNLESS>.
The file written with HTML and these new tags is called a template.
It is usually saved separate from your script - possibly even created
by someone else! Using this module you fill in the values for the
variables, loops and branches declared in the template. This allows
you to separate design - the HTML - from the data, which you generate
in the Perl script.
This module is licensed under the GPL. See the LICENSE section
below for more details.
=head1 TUTORIAL
If you're new to HTML::Template, I suggest you start with the
introductory article available on the HTML::Template website:
http://html-template.sourceforge.net
=head1 MOTIVATION
It is true that there are a number of packages out there to do HTML
templates. On the one hand you have things like HTML::Embperl which
allows you freely mix Perl with HTML. On the other hand lie
home-grown variable substitution solutions. Hopefully the module can
find a place between the two.
One advantage of this module over a full HTML::Embperl-esque solution
is that it enforces an important divide - design and programming. By
limiting the programmer to just using simple variables and loops in
the HTML, the template remains accessible to designers and other
non-perl people. The use of HTML-esque syntax goes further to make
the format understandable to others. In the future this similarity
could be used to extend existing HTML editors/analyzers to support
HTML::Template.
An advantage of this module over home-grown tag-replacement schemes is
the support for loops. In my work I am often called on to produce
tables of data in html. Producing them using simplistic HTML
templates results in CGIs containing lots of HTML since the HTML
itself cannot represent loops. The introduction of loop statements in
the HTML simplifies this situation considerably. The designer can
layout a single row and the programmer can fill it in as many times as
necessary - all they must agree on is the parameter names.
For all that, I think the best thing about this module is that it does
just one thing and it does it quickly and carefully. It doesn't try
to replace Perl and HTML, it just augments them to interact a little
better. And it's pretty fast.
=head1 THE TAGS
=head2 TMPL_VAR
<TMPL_VAR NAME="PARAMETER_NAME">
The <TMPL_VAR> tag is very simple. For each <TMPL_VAR> tag in the
template you call $template->param(PARAMETER_NAME => "VALUE"). When
the template is output the <TMPL_VAR> is replaced with the VALUE text
you specified. If you don't set a parameter it just gets skipped in
the output.
Optionally you can use the "ESCAPE=HTML" option in the tag to indicate
that you want the value to be HTML-escaped before being returned from
output (the old ESCAPE=1 syntax is still supported). This means that
the ", <, >, and & characters get translated into ", <, >
and & respectively. This is useful when you want to use a
TMPL_VAR in a context where those characters would cause trouble.
Example:
<input name=param type=text value="<TMPL_VAR NAME="PARAM">">
If you called param() with a value like sam"my you'll get in trouble
with HTML's idea of a double-quote. On the other hand, if you use
ESCAPE=HTML, like this:
<input name=param type=text value="<TMPL_VAR ESCAPE=HTML NAME="PARAM">">
You'll get what you wanted no matter what value happens to be passed in for
param. You can also write ESCAPE="HTML", ESCAPE='HTML' and ESCAPE='1'.
Substitute a 0 for the HTML and you turn off escaping, which is the default
anyway.
There is also the "ESCAPE=URL" option which may be used for VARs that
populate a URL. It will do URL escaping, like replacing ' ' with '+'
and '/' with '%2F'.
There is also the "ESCAPE=JS" option which may be used for VARs that
need to be placed within a Javascript string. All \n, \r, ' and " characters
are escaped.
You can assign a default value to a variable with the DEFAULT
attribute. For example, this will output "the devil gave me a taco"
if the "who" variable is not set.
The <TMPL_VAR NAME=WHO DEFAULT=devil> gave me a taco.
=head2 TMPL_LOOP
<TMPL_LOOP NAME="LOOP_NAME"> ... </TMPL_LOOP>
The <TMPL_LOOP> tag is a bit more complicated than <TMPL_VAR>. The
<TMPL_LOOP> tag allows you to delimit a section of text and give it a
name. Inside this named loop you place <TMPL_VAR>s. Now you pass to
param() a list (an array ref) of parameter assignments (hash refs) for
this loop. The loop iterates over the list and produces output from
the text block for each pass. Unset parameters are skipped. Here's
an example:
In the template:
<TMPL_LOOP NAME=EMPLOYEE_INFO>
Name: <TMPL_VAR NAME=NAME> <br>
Job: <TMPL_VAR NAME=JOB> <p>
</TMPL_LOOP>
In the script:
$template->param(EMPLOYEE_INFO => [
{ name => 'Sam', job => 'programmer' },
{ name => 'Steve', job => 'soda jerk' },
]
);
print $template->output();
The output in a browser:
Name: Sam
Job: programmer
Name: Steve
Job: soda jerk
As you can see above the <TMPL_LOOP> takes a list of variable
assignments and then iterates over the loop body producing output.
Often you'll want to generate a <TMPL_LOOP>'s contents
programmatically. Here's an example of how this can be done (many
other ways are possible!):
# a couple of arrays of data to put in a loop:
my @words = qw(I Am Cool);
my @numbers = qw(1 2 3);
my @loop_data = (); # initialize an array to hold your loop
while (@words and @numbers) {
my %row_data; # get a fresh hash for the row data
# fill in this row
$row_data{WORD} = shift @words;
$row_data{NUMBER} = shift @numbers;
# the crucial step - push a reference to this row into the loop!
push(@loop_data, \%row_data);
}
# finally, assign the loop data to the loop param, again with a
# reference:
$template->param(THIS_LOOP => \@loop_data);
The above example would work with a template like:
<TMPL_LOOP NAME="THIS_LOOP">
Word: <TMPL_VAR NAME="WORD"> <br>
Number: <TMPL_VAR NAME="NUMBER"> <p>
</TMPL_LOOP>
It would produce output like:
Word: I
Number: 1
Word: Am
Number: 2
Word: Cool
Number: 3
<TMPL_LOOP>s within <TMPL_LOOP>s are fine and work as you would
expect. If the syntax for the param() call has you stumped, here's an
example of a param call with one nested loop:
$template->param(LOOP => [
{ name => 'Bobby',
nicknames => [
{ name => 'the big bad wolf' },
{ name => 'He-Man' },
],
},
],
);
Basically, each <TMPL_LOOP> gets an array reference. Inside the array
are any number of hash references. These hashes contain the
name=>value pairs for a single pass over the loop template.
Inside a <TMPL_LOOP>, the only variables that are usable are the ones
from the <TMPL_LOOP>. The variables in the outer blocks are not
visible within a template loop. For the computer-science geeks among
you, a <TMPL_LOOP> introduces a new scope much like a perl subroutine
call. If you want your variables to be global you can use
'global_vars' option to new() described below.
=head2 TMPL_INCLUDE
<TMPL_INCLUDE NAME="filename.tmpl">
This tag includes a template directly into the current template at the
point where the tag is found. The included template contents are used
exactly as if its contents were physically included in the master
template.
The file specified can be an absolute path (beginning with a '/' under
Unix, for example). If it isn't absolute, the path to the enclosing
file is tried first. After that the path in the environment variable
HTML_TEMPLATE_ROOT is tried, if it exists. Next, the "path" option is
consulted, first as-is and then with HTML_TEMPLATE_ROOT prepended if
available. As a final attempt, the filename is passed to open()
directly. See below for more information on HTML_TEMPLATE_ROOT and
the "path" option to new().
As a protection against infinitly recursive includes, an arbitary
limit of 10 levels deep is imposed. You can alter this limit with the
"max_includes" option. See the entry for the "max_includes" option
below for more details.
=head2 TMPL_IF
<TMPL_IF NAME="PARAMETER_NAME"> ... </TMPL_IF>
The <TMPL_IF> tag allows you to include or not include a block of the
template based on the value of a given parameter name. If the
parameter is given a value that is true for Perl - like '1' - then the
block is included in the output. If it is not defined, or given a
false value - like '0' - then it is skipped. The parameters are
specified the same way as with TMPL_VAR.
Example Template:
<TMPL_IF NAME="BOOL">
Some text that only gets displayed if BOOL is true!
</TMPL_IF>
Now if you call $template->param(BOOL => 1) then the above block will
be included by output.
<TMPL_IF> </TMPL_IF> blocks can include any valid HTML::Template
construct - VARs and LOOPs and other IF/ELSE blocks. Note, however,
that intersecting a <TMPL_IF> and a <TMPL_LOOP> is invalid.
Not going to work:
<TMPL_IF BOOL>
<TMPL_LOOP SOME_LOOP>
</TMPL_IF>
</TMPL_LOOP>
If the name of a TMPL_LOOP is used in a TMPL_IF, the IF block will
output if the loop has at least one row. Example:
<TMPL_IF LOOP_ONE>
This will output if the loop is not empty.
</TMPL_IF>
<TMPL_LOOP LOOP_ONE>
....
</TMPL_LOOP>
WARNING: Much of the benefit of HTML::Template is in decoupling your
Perl and HTML. If you introduce numerous cases where you have
TMPL_IFs and matching Perl if()s, you will create a maintenance
problem in keeping the two synchronized. I suggest you adopt the
practice of only using TMPL_IF if you can do so without requiring a
matching if() in your Perl code.
=head2 TMPL_ELSE
<TMPL_IF NAME="PARAMETER_NAME"> ... <TMPL_ELSE> ... </TMPL_IF>
You can include an alternate block in your TMPL_IF block by using
TMPL_ELSE. NOTE: You still end the block with </TMPL_IF>, not
</TMPL_ELSE>!
Example:
<TMPL_IF BOOL>
Some text that is included only if BOOL is true
<TMPL_ELSE>
Some text that is included only if BOOL is false
</TMPL_IF>
=head2 TMPL_UNLESS
<TMPL_UNLESS NAME="PARAMETER_NAME"> ... </TMPL_UNLESS>
This tag is the opposite of <TMPL_IF>. The block is output if the
CONTROL_PARAMETER is set false or not defined. You can use
<TMPL_ELSE> with <TMPL_UNLESS> just as you can with <TMPL_IF>.
Example:
<TMPL_UNLESS BOOL>
Some text that is output only if BOOL is FALSE.
<TMPL_ELSE>
Some text that is output only if BOOL is TRUE.
</TMPL_UNLESS>
If the name of a TMPL_LOOP is used in a TMPL_UNLESS, the UNLESS block
output if the loop has zero rows.
<TMPL_UNLESS LOOP_ONE>
This will output if the loop is empty.
</TMPL_UNLESS>
<TMPL_LOOP LOOP_ONE>
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