my $popCt = 1;
my $markers = 2;

##</code><code>##

sub tester {
  my @holder = @{$HoH{$newcounter}{'holder'}};
  my @ind = @{$HoH{$newcounter}{'individual'}};
  my %HoHMarker = %{$HoH{$newcounter}{'marker'}};

##</code><code>##

my $newcounter = 1;
tester($newcounter);
#...
sub tester {
  my ($newcounter) = @_;
  ...
}

##</code><code>##

my $args = {
  arg1 => $arg1,
  arg2 => $arg2,
  arg3 => $arg3,
};
tester($args);
...
sub tester{
  my ($args) = @_;
  ...
}

##</code><code>##

sub tester {
  my @holder = @{$HoH{$newcounter}{'holder'}};
  die "tester: holder is empty" unless @holder;

##</code><code>##

my $success = tester();
die "tester failed" unless $success;

##</code><code>##

my %user_data_lookup;
...
my $safe_input = validate($user_input);
push @{$user_data_lookup{$safe_input}}, @some_array;
...