use HTML::TreeBuilder::XPath;

my $html = '<div><ul class="test">                 
<li><a href="/www/?category=Earth">earth_text</a></li>
<li><a href="/www/?category=Space">space_text</a></li></div>';

my $tree = HTML::TreeBuilder::XPath->new;
$tree->parse($html);
$tree->eof;

my @values = $tree->findvalues('//li/a');
print "$_\n" for @values;