title: How to check if input string contains a letter in TCL/TK scripting?
body: <p>I have a script which reads a list of integers from arguments and stores into a list then reverses its order.</p>
  
  <p>I am trying to look for a way to check if the input argument contains a letter so I can halt the program and throw a error message. Then exit the script.</p>
  
  <p>How can I check if a certain string has a letter? This letter can be uppercase or lowercase.</p>