macbook# perl -CSA -le 'printf("lowercase of U+%v04X <%s> is U+%v04X <%s>, uppercase of U+%v04X <%s> is U+%v04X <%s>\n", ($_)x2, (lc)x2, ($_)x2, (uc)x2) for @ARGV' ß ẞ
lowercase of U+00DF <ß> is U+00DF <ß>, uppercase of U+00DF <ß> is U+0053.0053 <SS>
lowercase of U+1E9E <ẞ> is U+00DF <ß>, uppercase of U+1E9E <ẞ> is U+1E9E <ẞ>