Help with program arguments please

I've read the manual but I am totally confused by all the {file} vs {filepath} vs {file$} etc.

All I want is a toolbar icon that will open my graphics program normally when clicked but will also accept a drag and drop to open a select file. I've tried lots of combinations but none give me what I want. Some will open the program but won't accept drag/drop. Others allow me to open with the selected file but won't open without one. Throw me a bone please.

Use {filepath} to get the full name + path to the file (instead of just its name without any path), and when you want it to be optional (so if nothing is selected or dropped and you click the button the program is run without any arguments).


Thank you. I could have sworn that I tried that one but you are correct, it works as I want it to.