I am not sure that you are asking for something like as: 
my $ret = '';
while (my ($file,$val) = each %hash) {
      $ret .= ">dataset\n";
      $ret .= "$file\n";
      $ret .= "instances\n";
      $ret .= join("\n",@{$val});
      $ret .= "\n";
}

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In reply to Re: Creating a Stringified Variable by pajout
in thread Creating a Stringified Variable from a Data Structure by monkfan

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