my %count;
while (...) {
  my($field1, $field2) = split(...);
  if (exists $count{$field1}) {
    # force the value to be array ref if it's
    # not done so
    $count{$field1} = [$count{$field1}]
      unless ref $count{$field1};
    push @{$count{$field1}}, $field2;
  }
  else {
    $count{$field1} = $field2; # normal assignment
  }
}