I'm trying to detect whether a command line option is a filename or a url and the perfect candidate would seem to be the ISFILE conditional, but it doesn't work. The following conditionals return False, as they should: ISFILE http ISFILE http: ISFILE http:/ The following conditional returns True (which is false): ISFILE http:// The second slash is the deciding factor. ISFILE always thinks the URL is a file. My purpose is to have a small BTM that will call Firefox with the correct command line, whether I'm trying to read a local HTML file, or go to a web page. I must be doing something wrong, but I'm having a senior moment.