Template(3)

NAME
HTML::Template - Perl module to use HTML Templates from CGI scripts

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

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.

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

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.

THE TAGS

  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'. 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.

  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">

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.

  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_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
HTML::Template's tags are meant to mimic normal HTML tags. However, they are allowed to "break the rules". Something like:

   <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.

METHODS

  new()
Call new() to create a new Template object:

  my $template = HTML::Template->new( filename => 'file.tmpl',
                                      option => 'value'
                                    );

You must call new() with at least one name => value pair specifying how to access the template text. You can use "filename => 'file.tmpl'" to specify a filename to be opened as the template. Alternately you can use:

  my $t = HTML::Template->new( scalarref => $ref_to_template_text,
                               option => 'value'
                             );

and

  my $t = HTML::Template->new( arrayref => $ref_to_array_of_lines ,
                               option => 'value'
                             );

These initialize the template from in-memory resources. In almost every case you'll want to use the filename parameter. If you're worried about all the disk access from reading a template file just use mod_perl and the cache option detailed below.

You can also read the template from an already opened filehandle, either traditionally as a glob or as a FileHandle:

  my $t = HTML::Template->new( filehandle => *FH, option => 'value');

The four new() calling methods can also be accessed as below, if you prefer.

  my $t = HTML::Template->new_file('file.tmpl', option => 'value');

  my $t = HTML::Template->new_scalar_ref($ref_to_template_text,
                                        option => 'value');

  my $t = HTML::Template->new_array_ref($ref_to_array_of_lines,
                                       option => 'value');

  my $t = HTML::Template->new_filehandle($fh,
                                       option => 'value');

And as a final option, for those that might prefer it, you can call new as:

  my $t = HTML::Template->new(type => 'filename',
                              source => 'file.tmpl');

Which works for all three of the source types.

If the environment variable HTML_TEMPLATE_ROOT is set and your filename doesn't begin with /, then the path will be relative to the value of $HTML_TEMPLATE_ROOT. Example - if the environment variable HTML_TEMPLATE_ROOT is set to "/home/sam" and I call HTML::Template->new() with filename set to "sam.tmpl", the HTML::Template will try to open "/home/sam/sam.tmpl" to access the template file. You can also affect the search path for files with the "path" option to new() - see below for more information.

You can modify the Template object's behavior with new(). The options are available:

Error Detection Options
    •   die_on_bad_params - if set to 0 the module will let you call $template->param(param_name => 'value') even if 'param_name' doesn't exist in the template body. Defaults to 1.

    •   strict - if set to 0 the module will allow things that look like they might be TMPL_* tags to get by without dieing. Example:

           <TMPL_HUH NAME=ZUH>

        Would normally cause an error, but if you call new with strict => 0, HTML::Template will ignore it. Defaults to 1.

    •   vanguard_compatibility_mode - if set to 1 the module will expect to see <TMPL_VAR>s that look like %NAME% in addition to the standard syntax. Also sets die_on_bad_params => 0. If you're not at Vanguard Media trying to use an old format template don't worry about this one. Defaults to 0.

Caching Options
    •   cache - if set to 1 the module will cache in memory the parsed templates based on the filename parameter and modification date of the file. This only applies to templates opened with the filename parameter specified, not scalarref or arrayref templates. Caching also looks at the modification times of any files included using <TMPL_INCLUDE> tags, but again, only if the template is opened with filename parameter.

        This is mainly of use in a persistent environment like Apache/mod_perl. It has absolutely no benefit in a normal CGI environment since the script is unloaded from memory after every request. For a cache that does work for normal CGIs see the 'shared_cache' option below.

        Note that different new() parameter settings do not cause a cache refresh, only a change in the modification time of the template will trigger a cache refresh. For most usages this is fine. My simplistic testing shows that using cache yields a 90% performance increase under mod_perl. Cache defaults to 0.

    •   shared_cache - if set to 1 the module will store its cache in shared memory using the IPC::SharedCache module (available from CPAN). The effect of this will be to maintain a single shared copy of each parsed template for all instances of HTML::Template to use. This can be a significant reduction in memory usage in a multiple server environment. As an example, on one of our systems we use 4MB of template cache and maintain 25 httpd processes - shared_cache results in saving almost 100MB! Of course, some reduction in speed versus normal caching is to be expected. Another difference between normal caching and shared_cache is that shared_cache will work in a CGI environment - normal caching is only useful in a persistent environment like Apache/mod_perl.

        By default HTML::Template uses the IPC key 'TMPL' as a shared root segment (0x4c504d54 in hex), but this can be changed by setting the 'ipc_key' new() parameter to another 4-character or integer key. Other options can be used to affect the shared memory cache correspond to IPC::SharedCache options - ipc_mode, ipc_segment_size and ipc_max_size. See IPC::SharedCache for a description of how these work - in most cases you shouldn't need to change them from the defaults.

        For more information about the shared memory cache system used by HTML::Template see IPC::SharedCache.

    •   double_cache - if set to 1 the module will use a combination of shared_cache and normal cache mode for the best possible caching. Of course, it also uses the most memory of all the cache modes. All the same ipc_* options that work with shared_cache apply to double_cache as well. By default double_cache is off.

    •   blind_cache - if set to 1 the module behaves exactly as with normal caching but does not check to see if the file has changed on each request. This option should be used with caution, but could be of use on high-load servers. My tests show blind_cache performing only 1 to 2 percent faster than cache under mod_perl.

        NOTE: Combining this option with shared_cache can result in stale templates stuck permanently in shared memory!

    •   file_cache - if set to 1 the module will store its cache in a file using the Storable module. It uses no additional memory, and my simplistic testing shows that it yields a 50% performance advantage. Like shared_cache, it will work in a CGI environment. Default is 0.

        If you set this option you must set the "file_cache_dir" option. See below for details.

        NOTE: Storable using flock() to ensure safe access to cache files. Using file_cache on a system or filesystem (NFS) without flock() support is dangerous.

    •   file_cache_dir - sets the directory where the module will store the cache files if file_cache is enabled. Your script will need write permissions to this directory. You'll also need to make sure the sufficient space is available to store the cache files.

    •   file_cache_dir_mode - sets the file mode for newly created file_cache directories and subdirectories. Defaults to 0700 for security but this may be inconvenient if you do not have access to the account running the webserver.

    •   double_file_cache - if set to 1 the module will use a combination of file_cache and normal cache mode for the best possible caching. The file_cache_* options that work with file_cache apply to double_file_cache as well. By default double_file_cache is 0.

Filesystem Options
    •   path - you can set this variable with a list of paths to search for files specified with the "filename" option to new() and for files included with the <TMPL_INCLUDE> tag. This list is only consulted when the filename is relative. The HTML_TEMPLATE_ROOT environment variable is always tried first if it exists. Also, if HTML_TEMPLATE_ROOT is set then an attempt will be made to prepend HTML_TEMPLATE_ROOT onto paths in the path array. In the case of a <TMPL_INCLUDE> file, the path to the including file is also tried before path is consulted.

        Example:

           my $template = HTML::Template->new( filename => 'file.tmpl',
                                               path => [ '/path/to/templates',
                                                         '/alternate/path'
                                                       ]
                                              );

        NOTE: the paths in the path list must be expressed as UNIX paths, separated by the forward-slash character ('/').

    •   search_path_on_include - if set to a true value the module will search from the top of the array of paths specified by the path option on every <TMPL_INCLUDE> and use the first matching template found. The normal behavior is to look only in the current directory for a template to include. Defaults to 0.

Debugging Options
    •   debug - if set to 1 the module will write random debugging information to STDERR. Defaults to 0.

    •   stack_debug - if set to 1 the module will use Data::Dumper to print out the contents of the parse_stack to STDERR. Defaults to 0.

    •   cache_debug - if set to 1 the module will send information on cache loads, hits and misses to STDERR. Defaults to 0.

    •   shared_cache_debug - if set to 1 the module will turn on the debug option in IPC::SharedCache - see IPC::SharedCache for details. Defaults to 0.

    •   memory_debug - if set to 1 the module will send information on cache memory usage to STDERR. Requires the GTop module. Defaults to 0.

Miscellaneous Options
    •   associate - this option allows you to inherit the parameter values from other objects. The only requirement for the other object is that it have a param() method that works like HTML::Template's param(). A good candidate would be a CGI.pm query object. Example:

          my $query = new CGI;
          my $template = HTML::Template->new(filename => 'template.tmpl',
                                             associate => $query);

        Now, $template->output() will act as though

          $template->param('FormField', $cgi->param('FormField'));

        had been specified for each key/value pair that would be provided by the $cgi->param() method. Parameters you set directly take precedence over associated parameters.

        You can specify multiple objects to associate by passing an anonymous array to the associate option. They are searched for parameters in the order they appear:

          my $template = HTML::Template->new(filename => 'template.tmpl',
                                             associate => [$query, $other_obj]);

        The old associateCGI() call is still supported, but should be considered obsolete.

        NOTE: The parameter names are matched in a case-insensitve manner. If you have two parameters in a CGI object like 'NAME' and 'Name' one will be chosen randomly by associate. This behavior can be changed by the following option.

    •   case_sensitive - setting this option to true causes HTML::Template to treat template variable names case-sensitively. The following example would only set one parameter without the "case_sensitive" option:

          my $template = HTML::Template->new(filename => 'template.tmpl',
                                             case_sensitive => 1);
          $template->param(
            FieldA => 'foo',
            fIELDa => 'bar',
          );

        This option defaults to off.

        NOTE: with case_sensitive and loop_context_vars the special loop variables are available in lower-case only.

    •   loop_context_vars - when this parameter is set to true (it is false by default) four loop context variables are made available inside a loop: __first__, __last__, __inner__, __odd__. They can be used with <TMPL_IF>, <TMPL_UNLESS> and <TMPL_ELSE> to control how a loop is output.

        In addition to the above, a __counter__ var is also made available when loop context variables are turned on.

        Example:

           <TMPL_LOOP NAME="FOO">
              <TMPL_IF NAME="__first__">
                This only outputs on the first pass.
              </TMPL_IF>

              <TMPL_IF NAME="__odd__">
                This outputs every other pass, on the odd passes.
              </TMPL_IF>

              <TMPL_UNLESS NAME="__odd__">
                This outputs every other pass, on the even passes.
              </TMPL_UNLESS>

              <TMPL_IF NAME="__inner__">
                This outputs on passes that are neither first nor last.
              </TMPL_IF>

              This is pass number <TMPL_VAR NAME="__counter__">.

              <TMPL_IF NAME="__last__">
                This only outputs on the last pass.
              </TMPL_IF>
           </TMPL_LOOP>

        One use of this feature is to provide a "separator" similar in effect to the perl function join(). Example:

           <TMPL_LOOP FRUIT>
              <TMPL_IF __last__> and </TMPL_IF>
              <TMPL_VAR KIND><TMPL_UNLESS __last__>, <TMPL_ELSE>.</TMPL_UNLESS>
           </TMPL_LOOP>

        Would output (in a browser) something like:

          Apples, Oranges, Brains, Toes, and Kiwi.

        Given an appropriate param() call, of course. NOTE: A loop with only a single pass will get both __first__ and __last__ set to true, but not __inner__.

    •   no_includes - set this option to 1 to disallow the <TMPL_INCLUDE> tag in the template file. This can be used to make opening untrusted templates slightly less dangerous. Defaults to 0.

    •   max_includes - set this variable to determine the maximum depth that includes can reach. Set to 10 by default. Including files to a depth greater than this value causes an error message to be displayed. Set to 0 to disable this protection.

    •   global_vars - normally variables declared outside a loop are not available inside a loop. This option makes <TMPL_VAR>s like global variables in Perl - they have unlimited scope. This option also affects <TMPL_IF> and <TMPL_UNLESS>.

        Example:

          This is a normal variable: <TMPL_VAR NORMAL>.<P>

          <TMPL_LOOP NAME=FROOT_LOOP>
             Here it is inside the loop: <TMPL_VAR NORMAL><P>
          </TMPL_LOOP>

        Normally this wouldn't work as expected, since <TMPL_VAR NORMAL>'s value outside the loop is not available inside the loop.

        The global_vars option also allows you to access the values of an enclosing loop within an inner loop. For example, in this loop the inner loop will have access to the value of OUTER_VAR in the correct iteration:

           <TMPL_LOOP OUTER_LOOP>
              OUTER: <TMPL_VAR OUTER_VAR>
                <TMPL_LOOP INNER_LOOP>
                   INNER: <TMPL_VAR INNER_VAR>
                   INSIDE OUT: <TMPL_VAR OUTER_VAR>
                </TMPL_LOOP>
           </TMPL_LOOP>

        NOTE: "global_vars" is not "global_loops" (which does not exist). That means that loops you declare at one scope are not available inside other loops even when "global_vars" is on.

    •   filter - this option allows you to specify a filter for your template files. A filter is a subroutine that will be called after HTML::Template reads your template file but before it starts parsing template tags.

        In the most simple usage, you simply assign a code reference to the filter parameter. This subroutine will recieve a single arguement - a reference to a string containing the template file text. Here is an example that accepts templates with tags that look like "!!!ZAP_VAR FOO!!!" and transforms them into HTML::Template tags:

           my $filter = sub {
             my $text_ref = shift;
             $$text_ref =~ s/!!!ZAP_(.*?)!!!/<TMPL_$1>/g;
           };

           # open zap.tmpl using the above filter
           my $template = HTML::Template->new(filename => 'zap.tmpl',
                                              filter => $filter);

        More complicated usages are possible. You can request that your filter receieve the template text as an array of lines rather than as a single scalar. To do that you need to specify your filter using a hash-ref. In this form you specify the filter using the "sub" key and the desired argument format using the "format" key. The available formats are "scalar" and "array". Using the "array" format will incur a performance penalty but may be more convenient in some situations.

           my $template = HTML::Template->new(filename => 'zap.tmpl',
                                              filter => { sub => $filter,
                                                          format => 'array' });

        You may also have multiple filters. This allows simple filters to be combined for more elaborate functionality. To do this you specify an array of filters. The filters are applied in the order they are specified.

           my $template = HTML::Template->new(filename => 'zap.tmpl',
                                              filter => [
                                                   { sub => \&decompress,
                                                     format => 'scalar' },
                                                   { sub => \&remove_spaces,
                                                     format => 'array' }
                                                ]);

        The specified filters will be called for any TMPL_INCLUDEed files just as they are for the main template file.

    •   default_escape - Set this parameter to "HTML", "URL" or "JS" and HTML::Template will apply the specified escaping to all variables unless they declare a different escape in the template.

  param()
param() can be called in a number of ways

1) To return a list of parameters in the template :

   my @parameter_names = $self->param();

2) To return the value set to a param :

   my $value = $self->param('PARAM');

3) To set the value of a parameter :

      # For simple TMPL_VARs:
      $self->param(PARAM => 'value');

      # with a subroutine reference that gets called to get the value
      # of the scalar.  The sub will recieve the template object as a
      # parameter.
      $self->param(PARAM => sub { return 'value' });

      # And TMPL_LOOPs:
      $self->param(LOOP_PARAM =>
                   [
                    { PARAM => VALUE_FOR_FIRST_PASS, ... },
                    { PARAM => VALUE_FOR_SECOND_PASS, ... }
                    ...
                   ]
                  );

4) To set the value of a a number of parameters :

     # For simple TMPL_VARs:
     $self->param(PARAM => 'value',
                  PARAM2 => 'value'
                 );

      # And with some TMPL_LOOPs:
      $self->param(PARAM => 'value',
                   PARAM2 => 'value',
                   LOOP_PARAM =>
                   [
                    { PARAM => VALUE_FOR_FIRST_PASS, ... },
                    { PARAM => VALUE_FOR_SECOND_PASS, ... }
                    ...
                   ],
                   ANOTHER_LOOP_PARAM =>
                   [
                    { PARAM => VALUE_FOR_FIRST_PASS, ... },
                    { PARAM => VALUE_FOR_SECOND_PASS, ... }
                    ...
                   ]
                  );

5) To set the value of a a number of parameters using a hash-ref :

      $self->param(
                   {
                      PARAM => 'value',
                      PARAM2 => 'value',
                      LOOP_PARAM =>
                      [
                        { PARAM => VALUE_FOR_FIRST_PASS, ... },
                        { PARAM => VALUE_FOR_SECOND_PASS, ... }
                        ...
                      ],
                      ANOTHER_LOOP_PARAM =>
                      [
                        { PARAM => VALUE_FOR_FIRST_PASS, ... },
                        { PARAM => VALUE_FOR_SECOND_PASS, ... }
                        ...
                      ]
                    }
                   );

  clear_params()
Sets all the parameters to undef. Useful internally, if nowhere else!

  output()
output() returns the final result of the template. In most situations you'll want to print this, like:

   print $template->output();

When output is called each occurrence of <TMPL_VAR NAME=name> is replaced with the value assigned to "name" via param(). If a named parameter is unset it is simply replaced with ''. <TMPL_LOOPS> are evaluated once per parameter set, accumlating output on each pass.

Calling output() is guaranteed not to change the state of the Template object, in case you were wondering. This property is mostly important for the internal implementation of loops.

You may optionally supply a filehandle to print to automatically as the template is generated. This may improve performance and lower memory consumption. Example:

   $template->output(print_to => *STDOUT);

The return value is undefined when using the "print_to" option.

  query()
This method allow you to get information about the template structure. It can be called in a number of ways. The simplest usage of query is simply to check whether a parameter name exists in the template, using the "name" option:

  if ($template->query(name => 'foo')) {
    # do something if a varaible of any type
    # named FOO is in the template
  }

This same usage returns the type of the parameter. The type is the same as the tag minus the leading 'TMPL_'. So, for example, a TMPL_VAR parameter returns 'VAR' from query().

  if ($template->query(name => 'foo') eq 'VAR') {
    # do something if FOO exists and is a TMPL_VAR
  }

Note that the variables associated with TMPL_IFs and TMPL_UNLESSs will be identified as 'VAR' unless they are also used in a TMPL_LOOP, in which case they will return 'LOOP'.

"query()" also allows you to get a list of parameters inside a loop (and inside loops inside loops). Example loop:

   <TMPL_LOOP NAME="EXAMPLE_LOOP">
     <TMPL_VAR NAME="BEE">
     <TMPL_VAR NAME="BOP">
     <TMPL_LOOP NAME="EXAMPLE_INNER_LOOP">
       <TMPL_VAR NAME="INNER_BEE">
       <TMPL_VAR NAME="INNER_BOP">
     </TMPL_LOOP>
   </TMPL_LOOP>

And some query calls:

  # returns 'LOOP'
  $type = $template->query(name => 'EXAMPLE_LOOP');

  # returns ('bop', 'bee', 'example_inner_loop')
  @param_names = $template->query(loop => 'EXAMPLE_LOOP');

  # both return 'VAR'
  $type = $template->query(name => ['EXAMPLE_LOOP', 'BEE']);
  $type = $template->query(name => ['EXAMPLE_LOOP', 'BOP']);

  # and this one returns 'LOOP'
  $type = $template->query(name => ['EXAMPLE_LOOP',
                                    'EXAMPLE_INNER_LOOP']);

  # and finally, this returns ('inner_bee', 'inner_bop')
  @inner_param_names = $template->query(loop => ['EXAMPLE_LOOP',
                                                 'EXAMPLE_INNER_LOOP']);

  # for non existent parameter names you get undef
  # this returns undef.
  $type = $template->query(name => 'DWEAZLE_ZAPPA');

  # calling loop on a non-loop parameter name will cause an error.
  # this dies:
  $type = $template->query(loop => 'DWEAZLE_ZAPPA');

As you can see above the "loop" option returns a list of parameter names and both "name" and "loop" take array refs in order to refer to parameters inside loops. It is an error to use "loop" with a parameter that is not a loop.

Note that all the names are returned in lowercase and the types are uppercase.

Just like "param()", "query()" with no arguements returns all the parameter names in the template at the top level.

FREQUENTLY ASKED QUESTIONS
In the interest of greater understanding I've started a FAQ section of the perldocs. Please look in here before you send me email.

1.  Q: Is there a place to go to discuss HTML::Template and/or get help?

    A: There's a mailing-list for discussing HTML::Template at html-template-users@lists.sourceforge.net. To join:

       http://lists.sourceforge.net/lists/listinfo/html-template-users

    If you just want to get email when new releases are available you can join the announcements mailing-list here:

       http://lists.sourceforge.net/lists/listinfo/html-template-announce

2.  Q: Is there a searchable archive for the mailing-list?

    A: Yes, you can find an archive of the SourceForge list here:

      http://www.geocrawler.com/lists/3/SourceForge/23294/0/

    For an archive of the old vm.com list, setup by Sean P. Scanlon, see:

       http://bluedot.net/mail/archive/

3.  Q: I want support for <TMPL_XXX>! How about it?

    A: Maybe. I definitely encourage people to discuss their ideas for HTML::Template on the mailing list. Please be ready to explain to me how the new tag fits in with HTML::Template's mission to provide a fast, lightweight system for using HTML templates.

    NOTE: Offering to program said addition and provide it in the form of a patch to the most recent version of HTML::Template will definitely have a softening effect on potential opponents!

4.  Q: I found a bug, can you fix it?

    A: That depends. Did you send me the VERSION of HTML::Template, a test script and a test template? If so, then almost certainly.

    If you're feeling really adventurous, HTML::Template has a publically available CVS server. See below for more information in the PUBLIC CVS SERVER section.

5.  Q: <TMPL_VAR>s from the main template aren't working inside a <TMPL_LOOP>! Why?

    A: This is the intended behavior. <TMPL_LOOP> introduces a separate scope for <TMPL_VAR>s much like a subroutine call in Perl introduces a separate scope for "my" variables.

    If you want your <TMPL_VAR>s to be global you can set the 'global_vars' option when you call new(). See above for documentation of the 'global_vars' new() option.

6.  Q: Why do you use /[Tt]/ instead of /t/i? It's so ugly!

    A: Simple - the case-insensitive match switch is very inefficient. According to _Mastering_Regular_Expressions_ from O'Reilly Press, /[Tt]/ is faster and more space efficient than /t/i - by as much as double against long strings. //i essentially does a lc() on the string and keeps a temporary copy in memory.

    When this changes, and it is in the 5.6 development series, I will gladly use //i. Believe me, I realize [Tt] is hideously ugly.

7.  Q: How can I pre-load my templates using cache-mode and mod_perl?

    A: Add something like this to your startup.pl:

       use HTML::Template;
       use File::Find;

       print STDERR "Pre-loading HTML Templates...\n";
       find(
            sub {
              return unless /\.tmpl$/;
              HTML::Template->new(
                                  filename => "$File::Find::dir/$_",
                                  cache => 1,
                                 );
            },
            '/path/to/templates',
            '/another/path/to/templates/'
          );

    Note that you'll need to modify the "return unless" line to specify the extension you use for your template files - I use .tmpl, as you can see. You'll also need to specify the path to your template files.

    One potential problem: the "/path/to/templates/" must be EXACTLY the same path you use when you call HTML::Template->new(). Otherwise the cache won't know they're the same file and will load a new copy - instead getting a speed increase, you'll double your memory usage. To find out if this is happening set cache_debug => 1 in your application code and look for "CACHE MISS" messages in the logs.

8.  Q: What characters are allowed in TMPL_* NAMEs?

    A: Numbers, letters, '.', '/', '+', '-' and '_'.

9.  Q: How can I execute a program from inside my template?

    A: Short answer: you can't. Longer answer: you shouldn't since this violates the fundamental concept behind HTML::Template - that design and code should be seperate.

    But, inevitably some people still want to do it. If that describes you then you should take a look at HTML::Template::Expr. Using HTML::Template::Expr it should be easy to write a run_program() function. Then you can do awful stuff like:

      <tmpl_var expr="run_program('foo.pl')">

    Just, please, don't tell me about it. I'm feeling guilty enough just for writing HTML::Template::Expr in the first place.

10. Q: Can I get a copy of these docs in Japanese?

    A: Yes you can. See Kawai Takanori's translation at:

       http://member.nifty.ne.jp/hippo2000/perltips/html/template.htm

11. Q: What's the best way to create a <select> form element using HTML::Template?

    A: There is much disagreement on this issue. My personal preference is to use CGI.pm's excellent popup_menu() and scrolling_list() functions to fill in a single <tmpl_var select_foo> variable.

    To some people this smacks of mixing HTML and code in a way that they hoped HTML::Template would help them avoid. To them I'd say that HTML is a violation of the principle of separating design from programming. There's no clear separation between the programmatic elements of the <form> tags and the layout of the <form> tags. You'll have to draw the line somewhere - clearly the designer can't be entirely in charge of form creation.

    It's a balancing act and you have to weigh the pros and cons on each side. It is certainly possible to produce a <select> element entirely inside the template. What you end up with is a rat's nest of loops and conditionals. Alternately you can give up a certain amount of flexibility in return for vastly simplifying your templates. I generally choose the latter.

    Another option is to investigate HTML::FillInForm which some have reported success using to solve this problem.

BUGS
I am aware of no bugs - if you find one, join the mailing list and tell us about it. You can join the HTML::Template mailing-list by visiting:

  http://lists.sourceforge.net/lists/listinfo/html-template-users

Of course, you can still email me directly (sam@tregar.com) with bugs, but I reserve the right to forward bug reports to the mailing list.

When submitting bug reports, be sure to include full details, including the VERSION of the module, a test script and a test template demonstrating the problem!

If you're feeling really adventurous, HTML::Template has a publically available CVS server. See below for more information in the PUBLIC CVS SERVER section.

CREDITS
This module was the brain child of my boss, Jesse Erlbaum ( jesse@vm.com ) at Vanguard Media ( http://vm.com ) . The most original idea in this module - the <TMPL_LOOP> - was entirely his.

Fixes, Bug Reports, Optimizations and Ideas have been generously provided by:

   Richard Chen
   Mike Blazer
   Adriano Nagelschmidt Rodrigues
   Andrej Mikus
   Ilya Obshadko
   Kevin Puetz
   Steve Reppucci
   Richard Dice
   Tom Hukins
   Eric Zylberstejn
   David Glasser
   Peter Marelas
   James William Carlson
   Frank D. Cringle
   Winfried Koenig
   Matthew Wickline
   Doug Steinwand
   Drew Taylor
   Tobias Brox
   Michael Lloyd
   Simran Gambhir
   Chris Houser <chouser@bluweb.com>
   Larry Moore
   Todd Larason
   Jody Biggs
   T.J. Mather
   Martin Schroth
   Dave Wolfe
   uchum
   Kawai Takanori
   Peter Guelich
   Chris Nokleberg
   Ralph Corderoy
   William Ward
   Ade Olonoh
   Mark Stosberg
   Lance Thomas
   Roland Giersig
   Jere Julian
   Peter Leonard
   Kenny Smith
   Sean P. Scanlon
   Martin Pfeffer
   David Ferrance
   Gyepi Sam
   Darren Chamberlain
   Paul Baker
   Gabor Szabo
   Craig Manley

Thanks!

WEBSITE
You can find information about HTML::Template and other related modules at:

   http://html-template.sourceforge.net

PUBLIC CVS SERVER
HTML::Template now has a publicly accessible CVS server provided by SourceForge (www.sourceforge.net). You can access it by going to http://sourceforge.net/cvs/?group_id=1075. Give it a try!

AUTHOR
Sam Tregar, sam@tregar.com

LICENSE
  HTML::Template : A module for using HTML Templates with Perl
  Copyright (C) 2000-2002 Sam Tregar (sam@tregar.com)

  This module is free software; you can redistribute it and/or modify it
  under the terms of either:

  a) the GNU General Public License as published by the Free Software
  Foundation; either version 1, or (at your option) any later version,

  or

  b) the "Artistic License" which comes with this module.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See either
  the GNU General Public License or the Artistic License for more details.

  You should have received a copy of the Artistic License with this
  module, in the file ARTISTIC.  If not, I'll be glad to provide one.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
  USA

POD ERRORS
Hey! The above document had some coding errors, which are explained below:

Around line 890:
    =back doesn't take any parameters, but you said =back 4