Question

I’m trying to write a subroutine in Perl that will delete a given node in XML when provided with the text values of some of the children nodes.

Given XML like:

<Path>
  <To>
    <My>
      <Node>
        <ChildA>ValA</ChildA>
        <ChildB>ValB</ChildB>
        <ChildC>ValC</ChildC>
      </Node>
    </My>
  </To>
</Path>
<!-- A lot of siblings follow... -->

The XPath expression I’m using is essentially:

/Path/To/My/Node[ChildA="ValA" and ChildB="ValB" and ChildC="ValC"]

When I’m trying to run my script, I’m getting an error like:

Error in XPath expression
/Path/To/My/Node[ChildA="ValA" and ChildB="ValB" and ChildC="ValC"] at 
ChildA="ValA" and ChildB="ValB" and ChildC="ValC" at Twig.pm line 3353

I’m at a loss for this and am looking for suggestions. I’ve tried googling around, but I can’t find working examples of trying to use predicates like this in XML::Twig. I don’t know if the problem is in my XPath syntax or how I’m using XML::Twig.

For good measure, I’ve also tried:

/Path/To/My/Node[ChildA/text()="ValA" and ChildB/text()="ValB" and ChildC/text()="ValC"]

No luck with that either. What is the solution?

Answer 1

Within the test, Node is the context node, so you have to say:

/Path/To/My/Node[./ChildA="ValA" and ./ChildB="ValB" and ./ChildC="ValC"]

This works for me in a short test program that uses XML::XPath.

EDIT: Sorry, I’m not so familiar with XML::Twig, and I made an incorrect assumption about its XPath capabilities. According to the documentation, it supports only an “XPath-like” syntax that doesn’t rise to the level of complexity of your example. However, if you use XML::Twig::XPath instead of XML::Twig, you get the full XPath engine:

my $twig = XML::Twig::XPath->new;
$twig->parse('your string');
my $nodes = $twig->findnodes('/Path/To/My/Node[ChildA="ValA" and ChildB="ValB" and ChildC="ValC"]');
print $nodes;

This prints “ValAValBValC”.