> my($what) = shift(@ARGV);
> my($whatLower) = $what;
> $whatLower =~ tr/[A-Z]/[a-z]/;

$whatLower = lc($what);

> if ($what eq undef)  {

well, if $what is undef you already have 2 
warnings before you detect it. On with tr/// (or lc()) and the next right here.
rather write:

my $what = shift @ARGV;
unless(  defined $what 
     and exists $dispatch{lc($what)}
){ Help(); exit defined($what) ? 0 : 1 }

$dispatch{$whatLower}->(@ARGV);
exit 0;