%functions = (
  '?' => 0,
  'HELLO' => sub { print "Hello, world.\n" },
  'HELP' => sub { print "Type 'hello' or 'goodbye'\n" },
  'GOODBYE' => sub { print "Goodbye...\n"; exit(0) }
);
# have to initialize this outside declaration of %functions
$functions{'?'} = $functions{'HELP'};

##</code><code>##

while(<>) {
  $func = $_;
  chomp($func);
  $func = uc($func);
  if( defined($functions{$func}) ) {
    ### insert code here to execute function in hash ###
  }
  else {
    print "\"$func\" not defined\n";
  }
}

##</code><code>##

    &$functions{$func};

##</code><code>##

    my $code;
    $code = $functions{$func};
    &$code;