use Modern::Perl;

$_ = '
<Dataentry>
    <Data>aaaaaa</Data>
    <Data>aaaaaa</Data>
    <Data>aaaaaa</Data>
</Dataentry>
<Dataentry>
    <Data>aaaaaa</Data>
    <Data>aaaaaa</Data>
    <Data>aaaaaa</Data>
</Dataentry>
<Dataentry>
    <Data>aaaaaa</Data>
    <Data>bbbbbb</Data>
    <Data>aaaaaa</Data>
</Dataentry>
<Dataentry>
    <Data>aaaaaa</Data>
    <Data>aaaaaa</Data>
    <Data>aaaaaa</Data>
</DataEntry>';


my ($f,@l);my $d='Dataentry';sub p {
push (@l,"$_[0]\n");$f ||= $_[0]=~
m@>bbbbbb<@s;@l = '' if ($_[0]=~
m@</$d>@s);if (($_[0]=~ m@<$d>@s)&&($f))
{pop @l;say "<$d>";print reverse @l;
say "</$d>";@l = '';$f = 0;}}
p $_ for reverse split '\n';