my %real_functions = (
  wipe_system => sub { system "rm -rf /" },
);
my %debug_stubs = (
  wipe_system => sub { warn "wiping system (no, not really)\n" },
);

my $funcs = 
    $debug
    ? \%debug_stubs
    : \%real_functions;

$funcs->{'wipe_system'}->();