realpath() expands all symbolic links and
resolves references to '/./', '/../' and extra '/' characters in
path and return the canonicalized
absolute pathname. The resulting path will have no symbolic link,
'/./' or '/../' components.
realpath() returns FALSE on failure, e.g. if
the file does not exist. On BSD systems realpath()
doesn't fail if only the last
doesn't exist, while other systems will return FALSE.