RailsErbStyle.rst

Style Guide for Rails Views

What do the ERb tags mean?

Basically, use <% %> and <%= %> where appropriate in your .html.erb files.

This is what the Rails API documentation says:

You trigger ERb by using embeddings such as <% %>, <%- -%>, and <%= %>. The <%= %> tag set is used when you want output. Consider the following loop for names:

<b>Names of all the people</b>
<% for person in @people %>
  Name: <%= person.name %><br/>
<% end %>

The loop is setup in regular embedding tags <% %> and the name is written using the output embedding tag <%= %>. Note that this is not just a usage suggestion. Regular output functions like print or puts won‘t work with ERb templates. So this would be wrong:

Hi, Mr. <% puts "Frodo" %>

If you absolutely must write from within a function, you can use the [[TextHelper#concat | http://api.rubyonrails.org/classes/ActionView/Helpers/TextHelper.html#M001710]]. See [[ActionView::Base | http://api.rubyonrails.org/]] for more details.

'<%- -%>' is the same as '<% %>'

Since <%- and -%> suppress leading and trailing whitespace, including the trailing newline and can be used interchangeably with <% and %>, we discourage using them in order to avoid confusion.

Comments in .html.erb files

If you are about to add comments in an .html.erb file use the following syntax, please:

<% # This is a comment
%>

as compared to:

<% # This is a comment %>

We think in the latter case, the closing <code>%></code> is ignored and causes errors in particular cases. So stick to the first syntax example!