<dependencies name="dependency">
  <poi org="ossjava" rev="3.6.0" />
</dependencies>

<dependencies>
       <dependency org="ossjava" name="poi" rev="3.6.0"/>
</dependencies>

use XML::LibXML qw( );

my $qfn = 'ivy.xml';

my $parser = XML::LibXML->new();
my $doc    = $parser->parse_file($qfn);
my $root   = $doc->documentElement();

for my $poi ($root->findnodes('//poi')) {
   $poi->setAttribute('rev', process($poi->getAttribute('rev')));
}

$doc->toFile($qfn);