I think I get what you mean. Let's say for example you want the right-most in the following string (which is stored in cell A1):
Drive:FolderSubFolderFilename.ext
To get the position of the last \, you would use this formula:
=FIND("@",SUBSTITUTE(A1,"","@",(LEN(A1)-LEN(SUBSTITUTE(A1,"","")))/LEN("")))
That tells us the right-most is at character 24. It does this by looking for "@" and substituting the very last "" with an "@". It determines the last one by using
(len(string)-len(substitute(string, substring, "")))len(substring)
In this scenario, the substring is simply "" which has a length of 1, so you could leave off the division at the end and just use:
=FIND("@",SUBSTITUTE(A1,"","@",LEN(A1)-LEN(SUBSTITUTE(A1,"",""))))
Now we can use that to get the folder path:
=LEFT(A1,FIND("@",SUBSTITUTE(A1,"","@",LEN(A1)-LEN(SUBSTITUTE(A1,"","")))))
Here's the folder path without the trailing
=LEFT(A1,FIND("@",SUBSTITUTE(A1,"","@",LEN(A1)-LEN(SUBSTITUTE(A1,"",""))))-1)
And to get just the filename:
=MID(A1,FIND("@",SUBSTITUTE(A1,"","@",LEN(A1)-LEN(SUBSTITUTE(A1,"",""))))+1,LEN(A1))
However, here is an alternate version of getting everything to the right of the last instance of a specific character. So using our same example, this would also return the file name:
=TRIM(RIGHT(SUBSTITUTE(A1,"",REPT(" ",LEN(A1))),LEN(A1)))