define rot13 use $str
    $str each chr
        dup m/[A-Ma-m]/ if
            ord 13 + chr
        else
            dup m/[N-Zn-z]/ if
               ord 13 - chr
    $str length list "" join

"12!ABJURER nowhere"
dup print "\nas rot13 is\n" print
rot13
print "\n" print