Ruby LanguageERB

Introduction

ERB stands for Embedded Ruby, and is used to insert Ruby variables inside templates, e.g. HTML and YAML. ERB is a Ruby class that accepts text, and evaluates and replaces Ruby code surrounded by ERB markup.

Syntax

  • <% number = rand(10) %> this code will be evaluated
  • <%= number %> this code will be evaluated and inserted into the output
  • <%# comment text %> this comment will not be evaluated

Remarks

Conventions:

  • ERB as a template: Abstract business logic into accompanied helper code, and keep your ERB templates clean and readable for people without Ruby knowledge.
  • Append files with .erb: e.g. .js.erb, .html.erb, .css.erb, etc.

Parsing ERB

This example is filtered text from an IRB session.

=> require 'erb'
=> input = <<-HEREDOC
<ul>
<% (0..10).each do |i| %>
    <%# This is a comment %>
    <li><%= i %> is <%= i.even? ? 'even' : 'odd' %>.</li>
<% end %>
</ul>
HEREDOC

=> parser = ERB.new(input)
=> output = parser.result
=> print output
<ul>


    <li>0 is even.</li>


    <li>1 is odd.</li>


    <li>2 is even.</li>


    <li>3 is odd.</li>


    <li>4 is even.</li>


    <li>5 is odd.</li>


    <li>6 is even.</li>


    <li>7 is odd.</li>


    <li>8 is even.</li>


    <li>9 is odd.</li>


    <li>10 is even.</li>

</ul>