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NAME
Template::Liquid - A Simple, Stateless Template System
Synopsis
use Template::Liquid;
my $template = Template::Liquid->parse(
'{% for x in (1..3) reversed %}{{ x }}, {% endfor %}{{ some.text }}');
print $template->render(some => {text => 'Contact!'}); # 3, 2, 1, Contact!
Description
The original Liquid template engine was crafted for very specific
requirements:
* It has to have simple markup and beautiful results.
Template engines which don't produce good looking results are no fun
to use.
* It needs to be non-evaling and secure.
Liquid templates are made so that users can edit them. You don't
want to run code on your server which your users wrote.
* It has to be stateless.
The compile and render steps have to be separate so the expensive
parsing and compiling can be done once; later on, you can just
render it by passing in a hash with local variables and objects.
* It needs to be able to style email as well as HTML.
Getting Started
It's very simple to get started. Templates are built and used in two
steps: Parse and Render.
If you're in a hurry, you could just...
use Template::Liquid;
print Template::Liquid->parse('Hi, {{name}}!')->render(name => 'Sanko');
But because Liquid is stateless, you can split that part. Keep reading.
Parse
use Template::Liquid;
my $sol = Template::Liquid->new(); # Create a Template::Liquid object
$sol->parse('Hi, {{name}}!'); # Parse and compile the template
...or...
use Template::Liquid;
my $sol = Template::Liquid->parse('Hi, {{name}}!'); # Obj is auto-created
The "parse" step creates a fully compiled template which can be re-used
as often as you like. You can store it in memory or in a cache for
faster rendering later. Templates are simple, blessed references so you
could do...
use Template::Liquid;
use Data::Dump qw[pp];
my $greet = Template::Liquid->parse('Hi, {{name}}!');
my $dump = pp($greet);
...store $dump somewhere (a file, database, etc.) and then eval the
structure later without doing the 'expensive' parsing step again.
Render
To complete our $sol examples from the previous section, rendering a
template is as easy as...
$sol->render(name => 'Sanko'); # Returns 'Hi, Sanko!'
$sol->render(name => 'Megatron'); # Returns 'Hi, Megatron!'
All parameters you want Template::Liquid to work with must be passed to
the "render" method. Template::Liquid is a closed ecosystem; it does not
know about your local, instance, global, or environment variables. If
your template requires any of those, you must pass them along:
use Template::Liquid;
print Template::Liquid->parse(
'@INC: {%for item in inc%}{{item}}, {%endfor%}')
->render(inc => \@INC);
Standard Liquid Tags
Expanding the list of supported tags is easy but here's the current
standard set:
"comment"
Comment tags are simple blocks that do nothing during the render stage.
Use these to temporarily disable blocks of code or to insert
documentation.
This is a {% comment %} secret {% endcomment %}line of text.
...renders to...
This is a line of text.
For more, see Template::Liquid::Tag::Comment.
"raw"
Raw temporarily disables tag processing. This is useful for generating
content (eg, Mustache, Handlebars) which uses conflicting syntax.
{% raw %}
In Handlebars, {{ this }} will be HTML-escaped, but {{{ that }}} will not.
{% endraw %}
...renders to...
In Handlebars, {{ this }} will be HTML-escaped, but {{{ that }}} will not.
For more, see Template::Liquid::Tag::Raw.
"if" / "elseif" / "else"
{% if post.body contains search_string %}
<div class="post result" id="p-{{post.id}}">
<p class="title">{{ post.title }}</p>
...
</div>
{% endunless %}
For more, see Template::Liquid::Tag::If and Template::Liquid::Condition.
.
"unless" / "elseif" / "else"
This is sorta the opposite of "if".
{% unless some.value == 3 %}
Well, the value sure ain't three.
{% elseif some.value > 1 %}
It's greater than one.
{% else %}
Well, is greater than one but not equal to three.
Psst! It's {{some.value}}.
{% endunless %}
For more, see Template::Liquid::Tag::Unless and
Template::Liquid::Condition.
"case"
If you need more conditions, you can use the case statement:
{% case condition %}
{% when 1 %}
hit 1
{% when 2 or 3 %}
hit 2 or 3
{% else %}
... else ...
{% endcase %}
For more, see Template::Liquid::Tag::Case.
"cycle"
Often you have to alternate between different colors or similar tasks.
Liquid has built-in support for such operations, using the cycle tag.
{% cycle 'one', 'two', 'three' %}
{% cycle 'one', 'two', 'three' %}
{% cycle 'one', 'two', 'three' %}
{% cycle 'one', 'two', 'three' %}
...will result in...
one
two
three
one
If no name is supplied for the cycle group, then it's assumed that
multiple calls with the same parameters are one group.
If you want to have total control over cycle groups, you can optionally
specify the name of the group. This can even be a variable.
{% cycle 'group 1': 'one', 'two', 'three' %}
{% cycle 'group 1': 'one', 'two', 'three' %}
{% cycle 'group 2': 'one', 'two', 'three' %}
{% cycle 'group 2': 'one', 'two', 'three' %}
...will result in...
one
two
one
two
For more, see Template::Liquid::Tag::Cycle.
"for"
Liquid allows for loops over collections:
{% for item in array %}
{{ item }}
{% endfor %}
Please see see Template::Liquid::Tag::For.
"assign"
You can store data in your own variables, to be used in output or other
tags as desired. The simplest way to create a variable is with the
assign tag, which has a pretty straightforward syntax:
{% assign name = 'freestyle' %}
{% for t in collections.tags %}{% if t == name %}
<p>Freestyle!</p>
{% endif %}{% endfor %}
Another way of doing this would be to assign true / false values to the
variable:
{% assign freestyle = false %}
{% for t in collections.tags %}{% if t == 'freestyle' %}
{% assign freestyle = true %}
{% endif %}{% endfor %}
{% if freestyle %}
<p>Freestyle!</p>
{% endif %}
If you want to combine a number of strings into a single string and save
it to a variable, you can do that with the capture tag.
For more, see Template::Liquid::Tag::Assign.
"capture"
This tag is a block which "captures" whatever is rendered inside it,
then assigns the captured value to the given variable instead of
rendering it to the screen.
{% capture attribute_name %}{{ item.title | handleize }}-{{ i }}-color{% endcapture %}
<label for="{{ attribute_name }}">Color:</label>
<select name="attributes[{{ attribute_name }}]" id="{{ attribute_name }}">
<option value="red">Red</option>
<option value="green">Green</option>
<option value="blue">Blue</option>
</select>
For more, see Template::Liquid::Tag::Capture.
Standard Liquid Filters
Please see Template::Liquid::Filters::Standard.
Extending Template::Liquid
Extending the Template::Liquid template engine for your needs is almost
too simple. Keep reading.
Custom Filters
Filters are simple subs called when needed. They are not passed any
state data by design and must return the modified content.
"Template::Liquid::register_filter( ... )"
This registers a package which Template::Liquid will assume contains one
or more filters.
# Register a package as a filter
Template::Liquid::register_filter( 'Template::Solution::Filter::Amalgamut' );
# Or simply say...
Template::Liquid::register_filter( );
# ...and Template::Liquid will assume the filters are in the calling package
Custom Tags
See the section entitled Extending Template::Liquid with Custom Tags in
Template::Liquid::Tag for more information.
To assist with custom tag creation, Template::Liquid provides several
basic tag types for subclassing and exposes the following methods:
"Template::Liquid::register_tag( ... )"
This registers a package which must contain (directly or through
inheritance) both a "parse" and "render" method.
# Register a new tag which Template::Liquid will look for in the calling package
Template::Liquid::register_tag( 'newtag' );
# Or simply say...
Template::Liquid::register_tag( 'newtag' );
# ...and Template::Liquid will assume the new tag is in the calling package
Pre-existing tags are replaced when new tags are registered with the
same name. You may want to do this to override some functionality.
For an example of a custom tag, see Solution::Tag::Include and
Solution::Tag::Dump.
Why should I use Template::Liquid?
* You want to allow your users to edit the appearance of your
application, but don't want them to run insecure code on your
server.
* You want to render templates directly from the database.
* You like Smarty-style template engines.
* You need a template engine which does HTML just as well as email.
* You don't like the markup language of your current template engine.
* You wasted three days reinventing this wheel when you could have
been doing something productive like volunteering or catching up on
past seasons of *Doctor Who*.
Why shouldn't I use Template::Liquid?
* You've found or written a template engine which fills your needs
better than Liquid or Template::Liquid ever could.
* You are uncomfortable with text that you didn't copy and paste
yourself. Everyone knows computers cannot be trusted.
Template::LiquidX or Solution?
I'd really rather use Solution::{Package} for extentions but who cares?
As I understand it, the original project's name, Liquid, is a reference
to the classical states of matter (the engine itself being stateless). I
settled on solution <http://en.wikipedia.org/wiki/Solution> because it's
liquid but... with... bits of other stuff floating in it. (Pretend you
majored in chemistry instead of mathematics or computer science.) Liquid
tempates will *always* work with Template::Liquid but (due to
Solutions's expanded syntax) Solution templates *may not* be compatible
with Liquid or Template::Liquid.
Author
Sanko Robinson <sanko@cpan.org> - http://sankorobinson.com/
CPAN ID: SANKO
The original Liquid template system was developed by jadedPixel
<http://jadedpixel.com/> and Tobias Lütke <http://blog.leetsoft.com/>.
License and Legal
Copyright (C) 2009-2013 by Sanko Robinson <sanko@cpan.org>
This program is free software; you can redistribute it and/or modify it
under the terms of The Artistic License 2.0
<http://www.perlfoundation.org/artistic_license_2_0>. See the LICENSE
file included with this distribution or notes on the Artistic License
2.0 <http://www.perlfoundation.org/artistic_2_0_notes> for
clarification.
When separated from the distribution, all original POD documentation is
covered by the Creative Commons Attribution-Share Alike 3.0 License
<http://creativecommons.org/licenses/by-sa/3.0/us/legalcode>. See the
clarification of the CCA-SA3.0
<http://creativecommons.org/licenses/by-sa/3.0/us/>.