Template::EmbeddedPerl - A template processing engine using embedding Perl code

use Template::EmbeddedPerl;

Create a new template object:

my $template = Template::EmbeddedPerl->new(); # default open and close tags are '<%' and '%>'

Compile a template from a string:

my $compiled = $template->from_string('Hello, <%= shift %>!');

#xecute the compiled template:

my $output = $compiled->render('John');

$output is:

Hello, John!

You can also use class methods to create compiled templates in one step if you don't need the reusable template object

my $compiled = Template::EmbeddedPerl->from_string('Hello, <%= shift %>!');
my $output = $compiled->render('John');

Or you can render templates from strings directly:

my $template = Template::EmbeddedPerl->new(use_cache => 1); # cache compiled templates
my $output = $template->render('Hello, <%= shift %>!', 'John');

Other class methods are available to create compiled templates from files, file handles, and data sections. See the rest of the docs for more information.

Template::EmbeddedPerl is a template engine that allows you to embed Perl code within template files or strings. It provides methods for creating templates from various sources, including strings, file handles, and data sections.

The module also supports features like helper functions, automatic escaping, and customizable sandbox environments.

Its quite similar to Mojo::Template and other embedded Perl template engines but its got one trick the others can't do (see EXCUSE below).

NOTE: This is a very basic template engine, which doesn't have lots of things you probably need like template includes / partials and so forth. That's by design since I plan to wrap this in a Catalyst view which will provide all those features. If you want to use this stand alone you might need to add those features yourself (or ideally put something on CPAN that wraps this to provide those features). Or you can pay me to do it for you ;)

I looked at Mojo::Template and I lifted some code and docs from there. I also copied some of their test cases. I was shooting for something reasonable similar and potentially compatible with Mojo::Template but with some additional features. Template::EmbeddedPerl is similiar to how template engines in popular frameworks like Ruby on Rails and also similar to EJS in the JavaScript world. So nothing weird here, just something people would understand and be comfortable with. A type of lowest common denominator. If you know Perl, you will be able to use this after a few minutes of reading the docs (or if you've used Mojo::Template or Mason you might not even need that).

Why create yet another one of these embedded Perl template engines? I wanted one that could properly handle block capture like following:

<% my @items = map { %>
  <p><%= $_ %></p>
<% } @items %>

Basically none of the existing ones I could find could handle this. If I'm wrong and somehow there's a flag or approach in Mason or one of the other ones that can handle this please let me know.

Mojo::Template is close but you have to use begin and end tags to get a similar effect and it's not as flexible as I'd like plus I want to be able to use signatures in code like the following:

<%= $f->form_for($person, sub($view, $fb, $person) { %>
  <div>
    <%= $fb->label('first_name') %>
    <%= $fb->input('first_name') %>
    <%= $fb->label('last_name') %>
    <%= $fb->input('last_name') %>
  </div>
<% }) %>

Again, I couldn't find anything that could do this. Its actually tricky because of the way you need to localize capture of template output when inside a block. I ended up using PPI to parse the template so I could properly find begin and end blocks and also distinguish between control blocks (like if an unless) blocks that have a return like sub or map blocks. In Mojo::Template you can do the following (its the same but not as pretty to my eye):

<% my $form = $f->form_for($person, begin %>
  <% my ($view, $fb, $person) = @_; %>
  <div>
    <%= $fb->label('first_name') %>
    <%= $fb->input('first_name') %>
    <%= $fb->label('last_name') %>
    <%= $fb->input('last_name') %>
  </div>
<% end; %>

On the other hand my system is pretty new and I'm sure there are bugs and issues I haven't thought of yet. So you probably want to use one of the more mature systems like Mason or Mojo::Template unless you really need the features I've added. Or your being forced to use it because you're working for me ;)

The template syntax is similar to other embedded Perl template engines. You can embed Perl code within the template using opening and closing tags. The default tags are '<%' and '%>', but you can customize them when creating a new template object. You should pick open and closing tags that are not common in your template content.

All templates get strict, warnings and utf8 enabled by default. Please note this is different than Mojo::Template which does not seem to have warnings enabled by default. Since I like very strict templates this default makes sense to me but if you tend to play fast and loose with your templates (for example you don't use my to declare variables) you might not like this. Feel free to complain to me, I might change it.

Basic Patterns:

<% Perl code %>
<%= Perl expression, replaced with result %>

Examples:

<% my @items = qw(foo bar baz) %>
<% foreach my $item (@items) { %>
  <p><%= $item %></p>
<% } %>

Would output:

<p>foo</p>
<p>bar</p>
<p>baz</p>

You can also use the 'line' version of the tags to make it easier to embed Perl code, or at least potentially easier to read. For example:

% my @items = qw(foo bar baz) % foreach my $item (@items) { <p><%= $item %></p> % }

You can add '=' to the closing tag to indicate that the expression should be trimmed of leading and trailing whitespace. This is useful when you want to include the expression in a block of text. where you don't want the whitespace to affect the output.

<% Perl code =%>
<%= Perl expression, replaced with result, trimmed =%>

If you want to skip the newline after the closing tag you can use a backslash.

<% Perl code %>\
<%= Perl expression, replaced with result, no newline %>\

You probably don't care about this so much with HTML since it collapses whitespace but it can be useful for other types of output like plain text or if you need some embedded Perl inside your JavaScript.

If you really need that backslash in your output you can escape it with another backslash.

<%= "This is a backslash: " %>\\

If you really need to use the actual tags in your output you can escape them with a backslash.

\<%       => <%
\<%=      => <%=
\%>       => %>
\%=       => %=
\%        => %

Lastly you can add full line comments to your templates that will be removed from the final output

# This is a comment
<p>Regular HTML</p>

A comment is declared with a single # at the start of the line (or with only whitespace preceeding it). This line will be removed from the output, including its newline. If you really need a '#'you can escape it with \# (this is only needed if the '#' is at the beginning of the line, or there's only preceding whitespace.

my $template = Template::EmbeddedPerl->new(%args);

Creates a new Template::EmbeddedPerl object. Accepts the following arguments:

• open_tag

  The opening tag for template expressions. Default is '<%'. You should use something that's not common in your template content.

• close_tag

  The closing tag for template expressions. Default is '%>'.

• expr_marker

  The marker indicating a template expression. Default is '='.

• sandbox_ns

  The namespace for the sandbox environment. Default is 'Template::EmbeddedPerl::Sandbox'. Basically the template is compiled into an anponymous subroutine and this is the namespace that subroutine is executed in. This is a security feature to prevent the template from accessing the outside environment.

• directories

  An array reference of directories to search for templates. Default is an empty array. A directory to search can be either a string or an array reference containing each part of the path to the directory. Directories will be searched in order listed.

    my $template = Template::EmbeddedPerl->new(directories=>['/path/to/templates']);
    my $template = Template::EmbeddedPerl->new(directories=>[['/path', 'to', 'templates']]);
  

  I don't do anything smart to make sure you don't reference templates in dangerous places. So be careful to make sure you don't let application users specify the template path.

• template_extension

  The file extension for template files. Default is 'epl'. So for example:

    my $template = Template::EmbeddedPerl->new(directories=>['/path/to/templates', 'path/to/other/templates']);
    my $compiled = $template->from_file('hello');
  

  Would look for a file named hello.epl in the directories specified.

• auto_escape

  Boolean indicating whether to automatically escape content. Default is 0. You probably want this enabled for web content to prevent XSS attacks. If you have this on and want to return actual HTML you can use the raw helper function. Example:

    <%= raw '<a href="http://example.com">Example</a>' %>
  

  Obviously you need to be careful with this.

• auto_flatten_expr

  Boolean indicating whether to automatically flatten expressions. Default is 1. What this means is that if you have an expression that returns an array we will join the array into a string before outputting it. Example:

    <% my @items = qw(foo bar baz); %>
    <%= map { "$_ " } @items %>
  

  Would output:

    foo bar baz
  

• preamble

  Add Perl code to the 'preamble' section of the compiled template. This is to top of the generated script prior to the anonymous sub representing your template.Default is an empty string. For example you can enable modern Perl features like signatures by setting this to 'use v5.40;'.

  Use this to setup any pragmas or modules you need to use in your template code.

• prepend

  Perl code to prepend to the compiled template. Default is an empty string. This goes just inside the anonyous subroutine that is called to return your document string. For example you can use this to pull passed arguments off @_.

• helpers

  A hash reference of helper functions available to the templates. Default is an empty hash. You can add your own helper functions to this hash and they will be available to the templates. Example:

    my $template = Template::EmbeddedPerl->new(helpers => {
      my_helper => sub { return 'Hello, World!' },
    });
  

• use_cache

  Boolean indicating whether to cache compiled templates. Default is 0. If you set this to 1, the module will cache compiled templates in memory. This is only useful if you are throwing away the template object after compiling a template. For example:

    my $ep = Template::EmbeddedPerl->new(use_cache => 1);
    my $output = $ep->render('Hello, <%= shift %>!', 'John');
  

  In the case above since you are not capturing the compiled template object each time you call render you are recompiling the template. which could get expensive.

  On the other hand if you are keeping the template object around and reusing it you don't need to enable this. Example:

    my $ep = Template::EmbeddedPerl->new(use_cache => 1);
    my $compiled = $ep->from_string('Hello, <%= shift %>!');
    my $output = $compiled->render('John');
  

  In the valid above the compiled template is cached and reused each time you call render.

  Obviously this only works usefully in a persistent environment like mod_perl or a PSGI server.

• comment_mark

  Defaults to '#'. Indicates the beginning of a comment in the template which is to be removed from the output. =back

my $compiled = $template->from_string($template_string, %args);

Creates a compiled template from a string. Accepts the template content as a string and optional arguments to modify behavior. Returns a Template::EmbeddedPerl::Compiled object.

pass 'source => $path' to the arguments to specify the source of the template if you want neater error messages.

This can be called as a class method as well::

my $compiled = Template::EmbeddedPerl->from_string($template_string, %args);

Useful if you don't need to keep the template object around. This works for all the other methods as well (from_file, from_fh, from_data).

my $compiled = $template->from_file($file_name, %args);

Creates a compiled template from a file. Accepts the filename (without extension) and optional arguments. Searches for the file in the directories specified during object creation.

my $compiled = $template->from_fh($filehandle, %args);

Creates a compiled template from a file handle. Reads the content from the provided file handle and processes it as a template.

pass 'source => $path' to the arguments to specify the source of the template if you want neater error messages.

my $compiled = $template->from_data($package, %args);

Creates a compiled template from the __DATA__ section of a specified package. Returns a compiled template object or dies if the package cannot be loaded or no __DATA__ section is found.

my $trimmed = $template->trim($string);

Trims leading and trailing whitespace from the provided string. Returns the trimmed string.

Same as trim but trims leading and trailing whitespace for a multiline string.

my %helpers = $template->default_helpers;

Returns a hash of default helper functions available to the templates.

my %helpers = $template->get_helpers($helper_name);

Returns a specific helper function or all helper functions if no name is provided.

my @parsed = $template->parse_template($template);

Parses the provided template content and returns an array of parsed blocks.

my $code = $template->compile($template, @parsed);

Compiles the provided template content into executable Perl code. Returns a code reference.

my $directory = $template->directory_for_package($package);

Returns the directory containing the package file. If you don't provide a package name it will use the current package for $template.

Useful if you want to load templates from the same directory as your package.

my $output = $template->render($template, @args);

Compiles and executes the provided template content with the given arguments. You might want to enable the cache if you are doing this.

The module provides a set of default helper functions that can be used in templates.

• raw

  Returns a string as a safe string object without escaping. Useful if you want to return actual HTML to your template but you better be sure that HTML is safe.

    <%= raw '<a href="http://example.com">Example</a>' %>
  

• safe

  Returns a string as a safe html escaped string object that will not be escaped again.

• safe_concat

  Like safe but for multiple strings. This will concatenate the strings into a single string object that will not be escaped again.

• html_escape

  Escapes HTML entities in a string. This differs for safe in that it will just do the escaping and not wrap the string in a safe string object.

• url_encode

  Encodes a string for use in a URL.

• escape_javascript

  Escapes JavaScript entities in a string. Useful for making strings safe to use in JavaScript.

• trim

  Trims leading and trailing whitespace from a string.

If an error occurs during template compilation or rendering, the module will throw an exception with a detailed error message. The error message includes the source of the template, the line number, and the surrounding lines of the template to help with debugging. Example:

Can't locate object method "input" at /path/to/templates/hello.yat line 4.

3:     <%= label('first_name') %>
4:     <%= input('first_name') %>
5:     <%= errors('last_name') %>

The module respects the following environment variables:

• DEBUG_TEMPLATE_EMBEDDED_PERL

  Set this to a true value to print the compiled template code to the console. Useful when trying to debug difficult compilation issues, especially given this is early access code and you might run into bugs.

If you find a bug, please report it on the GitHub issue tracker at https://github.com/jjn1056/Template-EmbeddedPerl/issues. The bug tracker is the easiest way to get help with this module from me but I'm also on irc.perl.org under jnap.

This module is dedicated to the memory of my dog Bear who passed away on 17 August 2024. He was a good companion and I miss him.

If this module is useful to you please consider donating to your local animal shelter or rescue organization.

John Napiorkowski, <jjnapiork@cpan.org>

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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

• Around line 765:

  You forgot a '=back' before '=head2'