title: Substring extraction in TCL
body: <p>I'm trying to extract a sequence of characters from a string in TCL.<br>
  Say, I have <code>"blahABC:blahDEF:yadamsg=abcd"</code>. <br>
  I want to extract the substring starting with <code>"msg="</code> until I reach the end of the string.<br> 
  Or rather I am interested in extracting <code>"abcd"</code> from the above example string.<br>
  Any help is greatly appreciated.<br>
  Thanks.<br></p>