Returns the extension from a file name, after stripping out the rest of the name
(vl-filename-extension filename)
Arguments
A string containing a file name, including the extension. The vl-filename-extension function does not check to see if the specified file exists.
Return Values
A string containing the extension of filename. The returned string starts with a period (.) and is in uppercase. If filename does not contain an extension, vl-filename-extension returns nil.
Examples
(vl-filename-extension "c:\\acadwin\\acad.exe") ".EXE" (vl-filename-extension "c:\\acadwin\\acad") nil