while(read_cmd()} {
  eval {
    $cmd_name=~/^\w+/ or die "invalid command";
    my $cmd_class = "MyApp::Command::$command_name";
    my $cmd = eval { require $cmd_class; $cmd_class->new };
    if ($@) die "unknow command $cmd_name ($@)\n";
    $cmd->parse_args(@args) or die "...";
    $cmd->run(@args) or die "...";
    etc();
  };
  print $@ if $@;
}