my %systems = (
  system1 => 'hostname_to_system1',
  system2 => 'hostname_to_system2',
  ...
);

my $choice = menu;
dftp( $systems{$choice} );

# sub menu {
  my @choices = (sort keys %systems)

  print "Please pick which system you wish to FTP to:\n";
  foreach my $i ( 0 .. $#choices ) {
     printf( "%2i.) %s\n", $i+1, @choices($i));
  }

  # get input ... assuming in $option;

  if ( $option eq 'q' ) {
    exit; # or an abort routine to handle cleaning up
  } elsif ( defined( $choices[$option-1] ) ) {
    return $choices[$option-1];
  } else {
    print "Unknown option.\nPlease try again\n";
    goto &menu;  # yes, goto.  Please don't give me the 'goto is evil' speach
  }
}