When do you use <% -%> instead of <% %>

I've noticed that in some lines of rails views, this is used:

<% # Code... -%>

instead of:

<% # Code... %>

What is the difference?

From stackoverflow

•     <ul>
      <% @posts.each do |post| -%> 
        <li><%=post.title%></li>
      <% end -%>
      </ul>
  

  There will be no new lines in between the <ul> and first <li> and the last closing </li> and </ul>. If the - was omitted, there would.

  Luke Francl : Yes. <% -%> suppresses new lines. It can be very useful when doing stuff in plain text (like emails) where that matters.

• Consider this

  <div>
      <% if @some_var == some_value %>
      <p>Some message</p>
      <% end %>
  </div>
  

  The code above yields to the HTML below if the @some_var is some_value

  <div>
  
      <p>Some message</p>
  
  </div>
  

  If you've put - in the closing tag, then the ERB interpreter would remove the new lines for those with code tag including - and result in the following

  <div>       
      <p>Some message</p>        
  </div>
  

  This is useful if you need to have a good looking code for HTML. Sometimes you'll find it useful when working sideby side with a designer

  Hope this helps.

• The different options for evaluating code in ERB are as follows (they can be accessed in Textmate using Ctrl-Shift-. ):

  • <% %> Just evaluate the contents.
  • <%= %> Evaluate the contents and puts the result.
  • <%= -%> Evaluate the contents and prints the result.
  • <%# %> The contents is treated as a comment and not outputted.

  Notice the difference between puts and print. Puts always adds a new line at the end of the string whereas print doesnt.

  Basically, the -%> says don't output a new line at the end.

• A little late, but I think it's worth pointing out that you can also do this:

  <%- @posts.each do |post| -%>
    <li><%= post.title %></li>
  <%- end %>
  

  This strips away any whitespace in front.