Hello, I was wondering if it is possible to have an option for which supplying an argument is optional. For example, suppose I have an executable called myprog and an option "o" that does something. Is it possible to allow both of the following command line syntaxes? myprog --o arg myprog --o Where in the second case I can programatically supply some default value? So the first would instruct the program to take the action associated with the "o" option using the supplied arg and the second would instruct it to take that action using the default argument value. I have been fooling with the default_value and implicit methods but neither seems to do what I want. Thanks, John Eddy johneddy@eng.buffalo.edu