Add an 'active' class to all active links in rails?

It's a solved problem, just use active_link_to gem. Your example simplifies to this:

= active_link_to t('.profile'), business_path(@business)

I wrote simple helper method using build in view helper current_page? when you can specify custom class name in html_options hash.

def active_link_to(name = nil, options = nil, html_options = nil, &block)
  active_class = html_options[:active] || "active"
  html_options.delete(:active)
  html_options[:class] = "#{html_options[:class]} #{active_class}" if current_page?(options)
  link_to(name, options, html_options, &block)
end

Examples (when you are on root_path route):

<%= active_link_to "Main", root_path %>
# <a href="/" class="active">Main</a>

<%= active_link_to "Main", root_path, class: "bordered" %>
# <a href="/" class="bordered active">Main</a>

<%= active_link_to "Main", root_path, class: "bordered", active: "disabled" %>
# <a href="/" class="bordered disabled">Main</a>