given ($a)
{
  when ('a') { print 1};
  when ('b') { print 2};
  ...
}

##</code><code>##

$\ = "\n"; # add a line break after each print, say could be used instead
for my $char (split //, "Hello World")
{
   if ($char =~ /[a-z]/) # if the char is between a and z
   {
      print 1 + ord($char) - ord('a');
   }
   else
   {
      print "Else";
   }
}