XML::LibXML::XPathContext findnodes() Question

AbrahamB has asked for the wisdom of the Perl Monks concerning the following question:

test.xml:

<?xml version="1.0" encoding="UTF-8"?>
<root>
  <element1>Element1 content</element1>
  <element2>Element2 content</element2>
</root>
[download]

Assuming I am using XML::LibXML correctly, does anyone have an idea why this returns expected result :

my $xpath = ‘/root’;
my $test = $doc->findnodes($xpath);
print Dumper($test);

$VAR1 = bless( [
                 bless( do{\(my $o = 13079328)}, 'XML::LibXML::Element
+' )
               ], 'XML::LibXML::NodeList' );
[download]

…But this returns empty array?

my $xpath = ’/root and /root/element1’;
my $test = $doc->findnodes($xpath);
print Dumper($test);

$VAR1 = bless( [], 'XML::LibXML::NodeList' );
[download]

Comment on XML::LibXML::XPathContext findnodes() Question Select or Download Code

Replies are listed 'Best First'.
Re: XML::LibXML::XPathContext findnodes() Question by Anonymous Monk on Dec 19, 2008 at 16:33 UTC
Context `#scalar my $test = $doc->findnodes($xpath); #list my @test = $doc->findnodes($xpath);` [download] wantarray	[reply] [d/l]
Re: XML::LibXML::XPathContext findnodes() Question by runrig (Abbot) on Dec 19, 2008 at 19:34 UTC
`my $xpath = ’/root and /root/element1’;` [download] How can you be at both /root and /root/element1 at the same time (and I'm not even sure that 'and' can be used even that way)? Do you mean?: `my $xpath = ’/root \| /root/element1’;` [download] Anyway, in your first case, it returns a NodeList object (which will contain no nodes), and in the second case, it returns an empty list (if there were nodes, it would return a list of Node objects)...due to the difference in the scalar vs. list context behavior of findnodes(), as implied in the post above.	[reply] [d/l] [select]
Re^2: XML::LibXML::XPathContext findnodes() Question by AbrahamB (Initiate) on Dec 19, 2008 at 20:54 UTC
I'm trying to test the existence of two separate elements. Like /root && /root/element1. I want true if both exist, false if one exists. The xpath can certainly be much better, but this is a simplified example from an xml-grep program I am working on. I'm trying to add the functionality to test for the existence of 2 nodes separated by ' and '. I may need to use find() or findvalue() for these types of xpaths. Thanks for your time!	[reply]
Re^3: XML::LibXML::XPathContext findnodes() Question by runrig (Abbot) on Dec 19, 2008 at 23:31 UTC
If /root/element1 exists, then /root certainly exists.	[reply]
Re^3: XML::LibXML::XPathContext findnodes() Question by roman (Monk) on Dec 20, 2008 at 10:00 UTC
You should probably use `$doc->findvalue` instead of findnodes because your XPath expression doesn't return a nodeset but boolean value. `warn $doc->findvalue('/root and /root/element1'), "\n"; warn $doc->findvalue('/root and /root/nosuch'), "\n";` [download] yields: `true false` [download]	[reply] [d/l] [select]


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