Then don't print the table, return it:

my $result = <<EOF;
print <<EOF;

<thead class="flip-content">
<tr>
<th width="20%"> Students id </th>
<th class="numeric"> First Name </th>
<th class="numeric"> Last Name </th>
<th class="numeric"> Date Of Birth </th>
<th class="numeric"> Year In </th>
<th class="numeric"> Password </th>
<th class="numeric"> Email </th>
<th class="numeric"> Telepon </th>
</tr>
</thead>

EOF

while (my @row_array = $sth->fetchrow_array()) {
$result .= <<EOF;
<tbody>
   <tr>
     <td> $row_array[0] </td>
     <td> $row_array[1] </td>
     <td> $row_array[2] </td>
     <td> $row_array[3] </td>
     <td> $row_array[4] </td>
     <td> $row_array[5] </td>
     <td> $row_array[6] </td>
     <td> $row_array[7] </td>
   </tr>
</tbody>
EOF
}
$result .= "</table>";   
return $result
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