The first error liverpole identified is easy to find if you turn on warnings (which you are not using in your code):

[10] perl -Mwarnings /tmp/testit.pl
"my" variable @perlbooks masks earlier declaration in same scope at /t
+mp/testit.pl line 50.
Bareword "parent" not allowed while "strict subs" in use at /tmp/testi
+t.pl line 15.
syntax error at /tmp/testit.pl line 34, near ")
        return"
Global symbol "@hrefs" requires explicit package name at /tmp/testit.p
+l line 34.
Execution of /tmp/testit.pl aborted due to compilation errors.
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The error stopping you from even compiling though, is the missing semicolon. 13 years of writing perl, and I still find missing semicolons, parens and braces are the hardest errors to find sometimes. I use perltidy now to try and help. For example, running your code through perltidy, I end up with:

sub get_url {
   my $node  = shift;
   my @hrefs = $node->look_down(_tag => 'a') return unless @hrefs;
   my $url   = $hrefs[0]->attr('href');
   $url =~ s/\s+$//;
   return $url;
}
[download]

Well, that long line jumped right out at me as being seriously wrong, and it was easy to figure out the fix then.

HTH,
~Jeff