XML::Twig question

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

I'm a little confused using the Perl XML::Twig module. What I'm trying to do is output a subset of the matched twig_root entries in an XML file. Essentially I call a method for the 'definition' twig_root and then I only want to output some of the definitions based on a condition. Of course I also want the root of the XML document to be output. It isn't. What am I doing wrong? I expect the <oval> tag and the selected <definition> and nothing else. I'm using the root <oval> tag.

XML

===

<?xml version="1.0" encoding="UTF-8"?> 
<oval xsi:schemaLocation="http://oval.mitre.org/XMLSchema/oval#redhat 
redhat-schema.xsd http://oval.mitre.org/XMLSchema/oval#windows 
windows-schema.xsd http://oval.mitre.org/XMLSchema/oval#unix 
unix-schema.xsd http://oval.mitre.org/XMLSchema/oval#independent 
independent-schema.xsd http://oval.mitre.org/XMLSchema/oval#solaris 
solaris-schema.xsd http://oval.mitre.org/XMLSchema/oval 
oval-schema.xsd" xmlns:oval="http://oval.mitre.org/XMLSchema/oval" 
xmlns="http://oval.mitre.org/XMLSchema/oval" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xmlns:redhat="http://oval.mitre.org/XMLSchema/oval#redhat" 
xmlns:windows="http://oval.mitre.org/XMLSchema/oval#windows"xmlns:sola
+ris="http://oval.mitre.org/XMLSchema/oval#solaris"> 
  <generator> 
    <schema_version>4.2</schema_version> 
    <timestamp>20051212102623</timestamp> 
  </generator> 
  <definitions> 
    <definition id="OVAL2" class="vulnerability"> 
      <affected family="redhat"> 
        <redhat:platform>Red Hat Linux 9</redhat:platform> 
        <product>Mutt</product> 
      </affected> 
    </definition> 
    <definition id="OVAL3" class="vulnerability"> 
      <affected family="windows"> 
        <windows:platform>Microsoft Windows 2000</windows:platform> 
        <windows:platform>Microsoft Windows Server 
2003</windows:platform> 
        <product>Microsoft Exchange Server 2003</product> 
      </affected> 
    </definition> 
    <definition id="OVAL6" class="vulnerability"> 
    </definition> 
  </definitions> 
  <crap>This is some crap</crap> 
</oval>
[download]

Perl code to extract a subset of the definitions

==================================

use XML::Twig; 


my $doc=new XML::Twig 
        ( 
                twig_roots => 
                { 
                        "definition" => \&parseEntry 
                } 
        ); 


sub parseEntry 
{ 
        my ($twig,$element)=@_; 


        my $id=$element->att("id"); 
        if ($id eq "OVAL3") 
        { 
                $element->flush(); 
                return 1; 
        } 


        $twig->purge(); 
        return 0; 



} 


$doc->parsefile("test.xml"); 
$doc->flush();
[download]

The output

========

  <definition class="vulnerability" id="OVAL3"> 
    <affected family="windows"> 
      <windows:platform>Microsoft Windows 2000</windows:platform> 
      <windows:platform>Microsoft Windows Server 
2003</windows:platform> 
      <product>Microsoft Exchange Server 2003</product> 
    </affected> 
  </definition> 
</oval>
[download]

Edit: g0n - readmore tags

Comment on XML::Twig question Select or Download Code

Replies are listed 'Best First'.
Re: XML::Twig question by mirod (Canon) on Dec 20, 2005 at 15:21 UTC
I think the `$twig->purge` is a little too strong for what you are doing. It seems to interfere with the way the twig is stored. Using `$element->delete` instead when the element is not one you want to output would work better. I will investigate some more to understand better what's going on, but in the mean time a handler like this seems to work: `sub parseEntry { my ($twig,$element)=@_; my $id=$element->att("id"); if ($id eq "OVAL3") { $twig->flush(); return 1; } else { $element->delete; } return 0; }` [download]	[reply] [d/l]
Re^2: XML::Twig question by rjkoop (Initiate) on Dec 21, 2005 at 01:35 UTC
That worked perfectly. Thanks.	[reply]