realpath() expands all symbolic links and
resolves references to '/./', '/../' and extra '/' characters in
the input 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 path component
doesn't exist, while other systems will return FALSE.
See also basename(), dirname(), and pathinfo().