Liquid for Programmers

First steps

It's very simple to get started with Liquid. A Liquid template is rendered in two steps: Parse and Render. For an overview of the Liquid syntax, please read Liquid for Designers.

@template = Liquid::Template.parse("hi {{name}}")  # Parses and compiles the template
@template.render( 'name' => 'tobi' )               # Renders the output => "hi tobi"

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.

All parameters you want Liquid to work with have to be passed as parameters to the render method. Liquid does not know about your Ruby local, instance, and global variables.

Extending Liquid

Extending Liquid is very easy. However, keep in mind that Liquid is a young library and requires some outside help. If you create useful filters and tags, please consider creating a patch and attaching it to a ticket here on this trac.

Create your own filters

Creating filters is very easy. Basically, they are just methods which take one parameter and return a modified string. You can use your own filters by passing an array of modules to the render call like this: @template.render(assigns, [MyTextFilters, MyDateFilters]).

module TextFilter
  def textilize(input)
    RedCloth.new(input).to_html
  end
end

@template = Liquid::Template.parse(" {{ '*hi*' | textilize }} ")
@template.render({}, :filters => [TextFilter])              # => "<b>hi</b>"

Alternatively, you can register your filters globally:

module TextFilter
  def textilize(input)
    RedCloth.new(input).to_html
  end
end

Liquid::Template.register_filter(TextFilter)

Once the filter is globally registered, you can simply use it:

@template = Liquid::Template.parse(" {{ '*hi*' | textilize }} ")
@template.render              # => "<b>hi</b>"

Create your own tags

To create a new tag, simply inherit from Liquid::Tag and register your block with Liquid::Template.

class Random < Liquid::Tag
  def initialize(tag_name, max, tokens)
     super
     @max = max.to_i
  end

  def render(context)
    rand(@max).to_s
  end
end

Liquid::Template.register_tag('random', Random)

@template = Liquid::Template.parse(" {% random 5 %}")
@template.render    # => "3"

Create your own tag blocks

All tag blocks are parsed by Liquid. To create a new block, you just have to inherit from Liquid::Block and register your block with Liquid::Template.

class Random < Liquid::Block
  def initialize(tag_name, markup, tokens)
     super
     @rand = markup.to_i
  end

  def render(context)
    if rand(@rand) == 0
       super
    else
       ''
    end
  end
end

Liquid::Template.register_tag('random', Random)

text = " {% random 5 %} wanna hear a joke? {% endrandom %} "
@template = Liquid::Template.parse(text)
@template.render  # => In 20% of the cases, this will output "wanna hear a joke?"