http://*.com/questions/998979/difference-between-and-in-rails/25617607#25617607

http://*.com/questions/7996695/what-is-the-difference-between-and-in-erb-in-rails

<% %>

Executes the ruby code within the brackets.

<%= %>

Prints something into erb file.

<% -%>

Avoids line break after expression.

<%# %>

Comments out code within brackets; not sent to client (as opposed to HTML comments).

In Ruby 2.1 (not necessarily with Rails), the - removes one trailing newline:

• the newline must be the first char after the >
• no spaces are removed
• only a single newline is removed
• you must pass the '-' option to use it

Examples:

require 'erb'

ERB.new("<%= 'a' %>\nb").result              == "a\nb"  or raise

begin ERB.new("<%= 'a' -%>\nb").result; rescue SyntaxError ; else raise; end

ERB.new("<%= 'a'  %>\nb"  , nil, '-').result == "a\nb"  or raise

ERB.new("<%= 'a' -%>\nb"  , nil, '-').result == 'ab'    or raise

ERB.new("<%= 'a' -%> \nb" , nil, '-').result == "a \nb" or raise

ERB.new("<%= 'a' -%>\n b" , nil, '-').result == 'a b'   or raise

ERB.new("<%= 'a' -%>\n\nb", nil, '-').result == "a\nb"  or raise