The most popular way to add Ruby code inside Rails views is with embedded Ruby (ERB). Files with embedded Ruby have the extension .html.erb and these files can have any amount of regular html markup.

Here’s the basic syntax:

<ul>
  <% @todo_items.each do |todo| %>
    <li><%= todo.name %> : <%= todo.priority %></li>
  <% end %>
</ul>

This will output html that looks like that:

<ul>
    <li>Buy milk : Normal</li>
    <li>Mow land : Urgent</li>
    <li>Throw a ball : Normal</li>
    <li>Learn Ruby : Extremely Urgent</li>
</ul>

Notice the use of <% with %> or <%= with %>. These tags are used to wrap Ruby code. The code following <% will be executed, but no output will be rendered. The code following <%= will have its result outputted in the html file.

Here’s a comment in ERB. These won’t be outputted in the html at all, not even as an html comment:

<%# Wild Things %>