I don’t have FMP 18, but I implemented a FileExists() function (one line of code in Java) about five years ago for FMP. This approach works with any version of FMP 12 or greater.
I can even post the code here if you want.
You pass the directory or file and it returns True or False. Forget about the “FMP ‘Specs’”. Instead, using a micro-service approach with a standard File API, there is NO artificial FMP limitation of what directory or file you pass it (because FMP isn’t in the mix for this function). The file or directory either exists or it doesn’t and could be anywhere addressable via mapping or volume – local or on a different machine or wherever.
You can set up a micro-service to add this method to in less than 2 minutes. See the link here on this site:
FMPDUDE-VIDEO: Creating a micro-service in a couple minutes (with FMP example)