Why the use of both <% and <%= in the views?
If I write something like:
<% if signed_in?.blank? %> or <%= link_to "Sign Up", sign_up_path %>
What is the difference between the two signs of <% and <%=?
Why make it this way instead of using just one for simplicity?
When do I know I need to use <% over <%=?
<%= puts the return value of the code inside to the page.
<% just execute code.
Here is the good guide about ERB http://api.rubyonrails.org/classes/ActionView/Base.html
<% %> Simply executes the statement(s) inside that block, whereas <%= %> will output the result of the statement.
So for example, with the <% if signed_in?.blank? %>, the ruby interpreter just executes that code and checks if signed_in is blank.
The <%= link_to %> statement will actually generate HTML.