title: Regex: replace all characters after 15th with '...'
body: <p>I am trying to do some simple formatting stuff with 'sed' in linux, and i need to use a regex to trim a string after the 15th character, and append a '...' to the end. Something like this:</p>
  
  <pre><code>before: this is a long string that needs to be shortened
  after: this is a long ...
  </code></pre>
  
  <p>Can anyone please show me how i could write this as a regex, and if possible explain how it works so that i might learn regex a little better?</p>