title: Extract substring from string with Regex
body: <p>Imagine that users are inserting strings in several computers.</p>
  
  <p>On one computer, the pattern in the configuration will extract some characters of that string, lets say position 4 to 5.
  On another computer, the extract pattern will return other characters, for instance, last 3 positions of the string.</p>
  
  <p>These configurations (the Regex patterns) are different for each computer, and should be available for change by the administrator, without having to change the source code.</p>
  
  <p>Some examples:</p>
  
  <pre><code>         Original_String       Return_Value
  User1 -  abcd78defg123         78
  User2 -  abcd78defg123         78g1
  User3 -  mm127788abcd          12
  User4 -  123456pp12asd         ppsd
  </code></pre>
  
  <p>Can it be done with Regex?
  Thanks.</p>