Success: On UNIX: [eclipse]: os_file_name("//a/b/c.def", OS). OS = "//a/b/c.def" yes On Windows: [eclipse]: os_file_name("//a/b/c.def", OS), write(OS). a:\b\c.def OS = "a:\\b\\c.def" yes [eclipse]: os_file_name(File, "a:\\b\\c.def"). File = "//a/b/c.def" yes Error: os_file_name(X, Y). (Error 4). os_file_name(4, X). (Error 5). os_file_name("/home/file", '/home/file'). (Error 5).