if    ($sel == 1) { show_installed() }
  elsif ($sel == 2) { show_available() }
  elsif ($sel == 3) { rgetpkglist()    }
  ...

##</code><code>##

  my %dispatch = (
    1 => \&show_installed,
    2 => \&show_available,
    3 => \&rgetpkglist,
    ...
  }

  $dispatch{$sel}->();