title: Change string char at index X
body: <p>I'm searched for a long time how to do a simple string manipulation in <code>UNIX</code></p>
  
  <p>I have this string:</p>
  
  <pre><code>theStr='...............'
  </code></pre>
  
  <p>And I need to change the 5th char to A, How can it be done?</p>
  
  <p>In <code>C#</code> it's done like this <code>theStr[4] = 'A'; // Zero based index.</code></p>