title: Change single variable value in querystring
body: <p>I am given a page url like <code>'http://abc.com/test.php?a=1&amp;b=2&amp;c=3'</code>. Now I have been told to change the value of b to 5 so that it becomes <code>'http://abc.com/test.php?a=1&amp;b=5&amp;c=3'</code>.</p>
  
  <p>i.e change from <code>http://abc.com/test.php?a=1&amp;b=2&amp;c=3</code> to <code>http://abc.com/test.php?a=1&amp;b=5&amp;c=3</code></p>
  
  <p>Note: variable b here can refer to any name.</p>