If @file_name ends with a directory separator it gets the component
before the last slash. If @file_name consists only of directory
separators (and on Windows, possibly a drive letter), a single
separator is returned. If @file_name is empty, it gets ".".
Gets the last component of the filename.
If @file_name ends with a directory separator it gets the component before the last slash. If @file_name consists only of directory separators (and on Windows, possibly a drive letter), a single separator is returned. If @file_name is empty, it gets ".".