my $acc;
my %handler = (
  1  => sub { $acc = $messagebin{$file}{1}; },
  11 => sub { ... },
);

if (my $code = $handler{+$subkey}) {
  $code->($subkey);
  # I found it convenient to have the dispatch value
  # available in the dispatch handler
} else {
  warn "Unhandled subkey value $subkey";
};