<% %>(without equal) in ruby erb means? [duplicate]

Answer 1

<% %>

Will execute Ruby code with no effect on the html page being rendered. The output will be thrown away.

<%= %>

Will execute Ruby code and insert the output of that code in place of the <%= %>

example...

<% puts "almost" %> nothing to see here 

would render as

nothing to see here

however

<%= puts "almost" %> nothing to see here

would render as

almost nothing to see here

Answer 2

Sometimes you will have to (or you want to) execute some ruby statements but not for output purpose.

like the following:

<% if @user.nil? %>
  Hi, welcome!
<% else %>
  Hi, <%= @user.name %>!
<% end %>

Of course this is just one use case, but sometimes you do need <% %> :D

Answer 3

Code in <% %>(without equal) is executed "with no substitution back into the output" means you want to execute code WITHOUT any output, like a loop and the best part is, it can be used with a non ruby code.

<% 3.times do %>

<h1>Hello world</h1>

<%end%>

This will give:

<h1>Hello world</h1>  
<h1>Hello world</h1>  
<h1>Hello world</h1>