Ruby ERB Templates

ERB (Embedded Ruby) is a powerful templating system in Ruby that allows you to embed Ruby code within HTML or other text documents. It's widely used for generating dynamic content in web applications, particularly with frameworks like Ruby on Rails.

What are ERB Templates?

ERB templates combine plain text with Ruby code snippets, enabling developers to create dynamic content easily. These templates are processed by the ERB library, which evaluates the embedded Ruby code and replaces it with the resulting output.

Basic Syntax

ERB uses special tags to embed Ruby code within a template:

• <%= %> - Evaluates Ruby code and outputs the result
• <% %> - Executes Ruby code without outputting the result
• <%# %> - Comments (not executed or output)

Example Usage

Here's a simple example of an ERB template:

<!-- greeting.erb -->
<h1>Hello, <%= name %>!</h1>
<p>Today is <%= Time.now.strftime("%A, %B %d, %Y") %>.</p>
<% if logged_in? %>
    <p>Welcome back!</p>
<% else %>
    <p>Please log in.</p>
<% end %>
    

To render this template in Ruby:

require 'erb'

name = "Alice"
logged_in = true

template = File.read('greeting.erb')
renderer = ERB.new(template)
result = renderer.result(binding)

puts result
    

Common Use Cases

ERB templates are frequently used in various scenarios:

• Generating HTML pages in web applications
• Creating email templates
• Producing configuration files
• Generating reports or documents

Best Practices

1. Keep logic in templates minimal. Complex operations should be handled in Ruby classes or helpers.
2. Use <%= %> for outputting values and <% %> for control structures.
3. Escape user input to prevent XSS attacks. In Rails, use <%= h(user_input) %> or <%= user_input.html_safe %> when appropriate.
4. Consider using partials for reusable template components.
5. Leverage Ruby String Interpolation within ERB for cleaner code.

Advanced Features

ERB offers advanced features for more complex templating needs:

• Trim mode: Control whitespace output with ERB.new(template, trim_mode: '-')
• Safe level: Set execution restrictions for untrusted templates
• Custom delimiters: Change the default <% and %> tags

Integration with Ruby Frameworks

ERB is tightly integrated with Ruby web frameworks:

• In Ruby on Rails, ERB is the default templating engine for views.
• Sinatra supports ERB out of the box for rendering templates.
• Many other Ruby frameworks and libraries use ERB for templating needs.

Understanding ERB is crucial for Ruby developers, especially those working on web applications. It bridges the gap between static content and dynamic Ruby code, enabling the creation of flexible and powerful templates.

Related Concepts

To deepen your understanding of Ruby and web development, explore these related topics:

• Ruby Modules for organizing code
• Ruby Blocks for creating reusable code snippets
• Ruby and HTTP for web communication