GENERAL TAG SYNTAX

template tags could be decorated as html comments <!-- TMPL_SOMETHING A="B" -->

Also, as HTML::Template::Pro extension (starting from version 0.90), template tags could also be decorated as xml <TMPL_SOMETHING A="B" />

See NOTES.

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 &quot;, &lt;, &gt; and &amp; 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'.

"ESCAPE=0" and "ESCAPE=NONE" turn off escaping, which is the default behavior.

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.

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.

TMPL_INCLUDE

  <TMPL_INCLUDE NAME="filename.tmpl">
  <TMPL_INCLUDE EXPR="function_call, variable, expression" DEFAULT='some_file'>

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 arbitrary 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.

For the <TMPL_INCLUDE EXPR=".."> see "INCLUDE extension to Expr" for more details.

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.

TMPL_ELSIF

  <TMPL_IF NAME="PARAMETER_NAME1"> ... 
  <TMPL_ELSIF NAME="PARAMETER_NAME2"> ... 
  <TMPL_ELSIF NAME="PARAMETER_NAME3"> ... 
  <TMPL_ELSE> ... </TMPL_IF>

WARNING: TMPL_ELSIF is a HTML::Template::Pro extension! It is not supported in HTML::Template (as of 2.9).

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>

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>
    ....
  </TMPL_LOOP>

NOTES

   <img src="<TMPL_VAR IMAGE_SRC>">

is not really valid HTML, but it is a perfectly valid use and will work as planned.

The "NAME=" in the tag is optional, although for extensibility's sake I recommend using it. Example - "<TMPL_LOOP LOOP_NAME>" is acceptable.

If you're a fanatic about valid HTML and would like your templates to conform to valid HTML syntax, you may optionally type template tags in the form of HTML comments. This may be of use to HTML authors who would like to validate their templates' HTML syntax prior to HTML::Template processing, or who use DTD-savvy editing tools.

  <!-- TMPL_VAR NAME=PARAM1 -->

In order to realize a dramatic savings in bandwidth, the standard (non-comment) tags will be used throughout this documentation.

Variables

   <TMPL_VAR EXPR="foo">
  
   <TMPL_VAR NAME="foo">

Emiliano Bruni extension to Expr

With this extension, arbitrary chars can be used in variable name inside the 'EXPR' tag if bracketed in ${}, as, for example, EXPR="${foo.bar} eq 'a'". Note that old bracketing into {} is considered obsolete, as it will clash with JSON assignments like A = { "key" => "val" }.

COMPATIBILITY WARNING. Currently, this extension is not present in HTML::Template::Expr (as of 0.04).

INCLUDE extension to Expr

SECURITY WARNING. Using of this extension with untrasted values of variables is a potential security leak (as in <TMPL_INCLUDE EXPR="USER_INPUT"> with USER_INPUT='/etc/passwd'). Omit it unless you know what you are doing.

COMPATIBILITY WARNING. Currently, this extension is not present in HTML::Template::Expr (as of 0.04).

Constants

   <TMPL_VAR EXPR="10 + 20.5">

String constants must be enclosed in quotes, single or double. For example:

   <TMPL_VAR EXPR="sprintf('%d', foo)">

Note that the original parser of HTML::Template::Expr is currently (0.04) rather simple, so if you need backward compatibility all compound expressions must be parenthesized.

Backward compatible examples:

   <TMPL_VAR EXPR="(10 + foo) / bar">

   <TMPL_IF EXPR="(foo % 10) > (bar + 1)">

Nevertheless, in HTML::Template::Pro, you can safely write things like

   <TMPL_VAR EXPR="1+2*foo/bar^2 ">

with proper priority of operations.

Pattern in a regular expression must be enclosed with "/":

   <TMPL_VAR EXPR="foo =~ /bar/">