When interpolated into a string, and array has it's elements seperated by $", which by default is a space, so your string ends up looking like "ford mustang 2003\n toyota landcruiser 1990....". Try using

{ 
  local $" = ""; 
  $gz->gzwrite("@{$hash_name{$hash_data}}");
}
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which will set $" to the empty string, which will then be put between each element.