Similar to ERB, Except Awesomer. 😉

Serbea is the Ruby template engine you didn’t realize you needed. Until now.

Serbea combines the best ideas from “brace-style” template languages such as Liquid, Nunjucks, Twig, Jinja, Mustache, etc.—and applies them to the world of ERB. You can use Serbea in Rails applications, Bridgetown static sites, or pretty much any Ruby scenario you could imagine.

Serbea. Finally, something to crow(n) about. Le roi est mort, vive le roi!

Table of Contents

Features and Syntax

What Serbea Looks Like

<!-- example.serb -->

{% wow = capture do %}
  This is {{ "amazing" + "!" | upcase }}
{% end %}

{% wow = wow.each_char.reduce("") do |newstr, c|
    newstr += " #{c}"
   end.strip %}

{{ wow | prepend: "OMG! " }}

Use helper (alias macro) to create ad-hoc filters:

    helper :multiply_array do |input, multiply_by = 2| do |i|
        i.to_i * multiply_by

  Multiply! {{ [1,3,6, "9"] | multiply_array: 10 }}

Forms, partials, etc. No sweat!

{%= form classname: "checkout" do |f| %}
  {{ f.input :first_name, required: true | errors: error_messages }}
{% end %}

{%= render "box" do %}
  This is **dope!**
  {%= render "card", title: "Nifty!" do %}
    So great.
  {% end %}
{% end %}

Let’s simplify that using the render directive!

{%@ "box" do %}
  This is **dope!**
  {%@ "card", title: "Nifty!" do %}
    So great.
  {% end %}
{% end %}

Works with ViewComponent! And we can use the render directive!

{%@ Theme::DropdownComponent name: "banner", label: "Banners" do |dropdown| %}
  {% RegistryTheme::BANNERS.each do |banner| %}
    {% dropdown.slot(:item, value: banner) do %}
      <img src="{{ banner | parameterize: separator: "_" | prepend: "/themes/" | append: ".jpg" }}">
      <strong>{{ banner }}</strong>
    {% end %}
  {% end %}
{% end %}

The | and |> pipeline operators are equivalent, so you can write like this if you want!

  [1,2,3] |>
    map: -> i { i * 10 }
    filter: -> i do
      i > 15 # works fine with multiline blocks
    assign_to: :array_length

Array length: {{ @array_length.length }}

The answer of course is: 2

Installation and Usage

(For Rails and Bridgetown scenarios, see below.)

Simply add the Serbea gem to your Gemfile:

bundle add serbea

or install standalone:

gem install serbea

Serbea templates are typically saved using a .serb extension. If you use VS Code as your editor, there is a VS Code extension to enable Serbea syntax highlighting as well as palette commands to convert selected ERB syntax to Serbea.

To convert Serbea code in a basic Ruby script, all you have to do is require the Serbea gem, include the necessary helpers module, and use the Tilt interface to load and render the template. Example:

require "serbea"
include Serbea::Helpers

tmpl = { "Hello {{ world | append: '!' }}" }
tmpl.render(self, world: "World")

# Hello World!

You’ll likely want to bind to a dedicated view object instead of self as in the example above, since that view object can include the Serbea helpers without fear of any collision with existing object methods in your codebase.

Serbea helpers include pipeline which faciliates the {{ }} template syntax, capture, helper, safe, escape, and assign_to.

Bridgetown Support

If you’re using Bridgetown 1.0, Serbea is automatically included! See Serbea-specific documentation here.

Serbea is an excellent upgrade from Liquid as the syntax initially looks familar, yet it enbles the full power of real Ruby in your templates.

Out of the box, you can name pages and partials with a .serb extension. But for even more flexibility, you can add template_engine: serbea to your bridgetown.config.yml configuration. This will default all pages and documents to Serbea unless you specifically use front matter to choose a different template engine (or use an extension such as .liquid or .erb).

Here’s an abreviated example of what the Post layout template looks like on the Fullstack Ruby blog:

layout: bulmatown/post

<div class="content-column">{%= yield %}</div>

{{ liquid_render "subscribe" }}

{% if %}
  <p class="mt-6 is-size-7 has-text-centered">
    <em>Banner image by <a href="{{ | safe }}">
      {{ }}
{% end %}

{% posts = page.related_posts[0...2] %}
{{ liquid_render "bulmatown/collection", collection: posts, metadata: site.metadata }}

{% if page.related_posts.size > 2 %}
  <a href="/articles">Read More Articles</a>
{% end %}

{%= markdownify do %}
  {{ liquid_render "sponsor" }}
{% end %}

Rails Support

To use in Rails, run:

bundle add serbea-rails

Serbea fully supports Rails (tested with Rails 6), and even includes special directives for Turbo Streams as highlighted above.

Simply use the .serb extension wherever you would use .erb normally. You can freely mix ‘n’ match Serbea templates with other template engines, so for instance index.html.erb and show.html.serb can live side-by-side.

Note: if you use a Serbea template as a layout, you may encounter some subtle rendering issues with ERB page templates that use the layout. It is recommended you use Serbea for layouts only if you intend to standardize on Serbea for your application.

Upgrade your helpers! While you can use the same kind of syntax for helpers you may be accustomed to in ERB, using the pipeline syntax can be far more enjoyable and better express intent. For example, instead of confusing nested method calls like this:

Here's a <%= link_to(highlight("  link for you  ".strip.titleize, "you"), other_page_path) %>

You could instead write this:

Here's a {{ "  link for you  " | strip | titleize | highlight: "you" | link_to: other_page_path }}

which is far easier to parse visually and less likely to cause bugs due to nesting errors.

Stay Safe! In pipelines, Serbea uses the same safe escaping logic you’ve experienced with ERB. So if you were to put {{ "<p>Aha!</p>" }} in a template, you don’t get an HTML paragraph, you get the literal characters of the p tags. You would have to use the safe (aliased raw) filter in order to get working HTML output. However, that is NOT the case with expressions. {%= "<p>Bingo!</p>" %} outputs that text verbatim and you get a valid HTML paragraph. So use expressions sparingly and only in cases where you know the values have already been cleansed (e.g., rendering partials or components, using form helpers, yielding in layouts, etc.). Alternatively, you can use the escape (aliased h) helper: {%= escape "<p>Bingo!</p>" %}.

Add Pipelines to Any Ruby Templates

New in Serbea 2.0, you can use a pipeline operator (|) within a pipe block to construct a series of expressions which continually operate on the latest state of the base value.

All you have to do is include Serbea::Pipeline::Helper inside of any Ruby class or template environment (aka ERB).

Here’s a simple example:

class PipelineExample
  include Serbea::Pipeline::Helper

  def output
    pipe("Hello world") { upcase | split(" ") | test_join(", ") }

  def test_join(input, delimeter)
end # => HELLO, WORLD

As you can see, a number of interesting things are happening here. First, we’re kicking off the pipeline using a string value. This then lets us access the string’s upcase and split methods. Once the string has become an array, we pipe that into our custom test_join method where we can call the array value’s join method to convert it back to a string. Finally, we return the output value of the pipeline.

Like in native Serbea template pipelines, every expression in the pipeline will either call a method on the value itself, or a filter-style method that’s available within the calling object. As you might expect in, say, an ERB template, all of the helpers are available as pipeline filters. In Rails, for example:

Link: <%= pipe("nav.page_link") { t | link_to(my_page_path) } %>

This is roughly equivalent to:

Link: <%= link_to(t("nav.page_link"), my_page_path) %>

The length of the pipe code is slightly longer, but it’s easier to follow the order of operations:

  1. First, you start with the translation key.
  2. Second, you translate that into official content.
  3. Third, you pass that content to link_to along with a URL helper.

There are all sorts of uses for a pipeline, not just in templates. You could construct an entire data flow with many transformation steps. And because the pipeline operator | is actually optional when using a multi-line block, you can just write a series of simple Ruby statements:

def transform(input_value)
  pipe input_value do
    convert_to_whatever # maybe this is called on the value object itself
    value ->{ AnotherClass.operate_on_value _1 } # return a new value from outside processing

def transform_this_way(input) = ...
def transform_that_way(input) = ...
def add_more_data(input, data) = ...
def now_we_are_done!(input) = ...


How Pipelines Work Under the Hood

In Serbea templates, code which looks like this:

{{ data | method_call | some_filter: 123 }}

gets translated to this:

pipeline(data).filter(:method_call).filter(:some_filter, 123)

In plain Ruby, method_missing is used to proxy method calls along to filter, so:

pipe(data) { method_call | some_filter(123) }

is equivalent to:

pipe(data) { filter(:method_call); filter(:some_filter, 123) }

Pipelines “inherit” their calling context by using Ruby’s binding feature. That’s how they know how to call the methods which are available within the caller.

Another interesting facet of Serbea pipelines is that they’re forgiving by default. If a filter can’t be found (either there’s no method available to call the object itself nor is there a separate helper method), it will log a warning to STDERR and continue on. This is to make the syntax feel a bit more like HTML and CSS where you can make a mistake or encounter an unexpected error condition yet not crash the entire application.

If you do want to crash your entire application (😜), you can set the configuration option: Serbea::Pipeline.raise_on_missing_filters = true. This will raise a Serbea::FilterMissing error if a filter can’t be found.

Note: if you find that a certain method doesn’t work within a pipeline when writing plain Ruby, because that method has polluted the global Object set of instance methods, you can call Serbea::Pipeline.polluted_method(:method_name_here) to strip that off and allow filtering to work. It also accepts an array of symbols.

Note: if you find that a certain filter is being called as a method directly on the value object, rather than a defined filter method itself, you can add that method name to a deny list via Serbea::Pipeline.deny_value_method(:method_name_here). It also accepts an array of symbols.