title: How do i forbid a character in rails
body: <p>i would like to forbid "/" from a field.</p>
  
  <p>I read in the doc that it should be something like that:</p>
  
  <blockquote>
    <p>valid_name_regex = /<br>
    validates :name, presence: true,
                       uniqueness: { case_sensitive: true }, format: { with: valid_name_regex }</p>
  </blockquote>
  
  <p>But i'd like the opposite.</p>
  
  <p>thanks</p>