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

Hello there, I'm trying to find and replace a string value in XML. I've the below code so far. 

  #!C:/Perl/bin/perl.exe -w 

  #use strict; 

  use XML::XPath;
  use Data::Dumper;
  use XML::XPath::XMLParser; 

  my $xp = XML::XPath->new(filename => "new.xml"); 
 
  my $nodeset = $xp->findnodes('/catalog/book/titles/title');
  my @n = ("value one", "value two");
  print $nodeset->size;
  
  my $i = 0;
  
  foreach my $node ($nodeset->get_nodelist) {
   
    print "\nGET: " . $xp->getNodeText($node) . "\n";
    print "\nSET: " . $xp->setNodeText('/catalog/book/titles/title['."
+$i+1".']', $n[$i]) . "\n";
   
    $i++;
  }
  
  open('FILE', '>output.xml');
  my $nodes = $xp->find('/');  
  foreach my $node ($nodes->get_nodelist) {
        print FILE XML::XPath::XMLParser::as_string($node);
  }
 
  close(FILE);

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My sample XML file 

<?xml version="1.0"?>
<catalog>
   <book>
      <author>Gambardella, Matthew</author>
      <titles>
         <title>Book 1 </title>
         <title>Book 2 </title>
      </titles>
      <genre>Computer</genre>
      <price>44.95</price>
      <publish_date>2000-10-01</publish_date>
      <description>An in-depth look at creating applications 
      with XML.</description>
   </book>
   <book>
      <author>Ralls, Kim</author>
         <titles>
         <title>Book 3 </title>
         <title>Book 4 </title>
      </titles>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-12-16</publish_date>
      <description>A former architect battles corporate zombies, 
      an evil sorceress, and her own childhood to become queen 
      of the world.</description>
   </book>
   </catalog>

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I need to pass each node value to the setNodeText method. The XPath I've currently sets two child nodes at a time.

For example, I'd like to retrieve Book 1 through 4 one at a time and set each node value to a different value. In my code, when I try to set Book 1, it sets Book 3 to the same value. Likewise, when I try to set Book 2, the value of Book 4 is overwritten. Is there a way that I could pass one node to the setNodeText() method?

I appreciate any input.

Thanks

Replies are listed 'Best First'.
Re: Perl XPath
by Corion (Patriarch) on Feb 27, 2012 at 19:27 UTC

    Your code affects two title nodes at once because your XPath expression matches two title nodes: 

    /catalog/book/titles/title[ $i+1 ]

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    You will need to either make your XPath expression match the specific book you are currently modifying:

    /catalog/book[ $j ]/titles/title[ $i+1 ]

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    ... or you have to remove the text node from the current element and append your own text node. See XML::LibXML::Element->appendTextChild and XML::LibXML::Node->removeChildNodes:

    my $element = ...;
$element->removeChildNodes();
$element->appendTextNode("Hello!");

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      Hi,

      Thanks for your response.

      Is there a way that I could pass a node to setNodeText()? I'm able to retrieve the different node values using getNodeText() method by passing the $node parameter. I'm assuming that I could do the same for setNodeText() method but somehow the method doesn't recognize the $node in XPath.

      Thanks

[reply]

        I assume once you have the XML::LibXML::Text node, you can use ->replaceData or ->setData to change the values. But I've never done anything like it using XML::LibXML, so you'll have to find out whether it works yourself.

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Re: Perl XPath
by BrowserUk (Patriarch) on Feb 28, 2012 at 20:53 UTC

    Try this. It takes 3 seconds to update a generated file containing 1000 books (2000 titles):

    #! perl -slw
use strict;
use Data::Dump qw[ pp ];
use XML::Simple;

my $start = time;

my $xml = XMLin( \*STDIN, KeepRoot => 1 );
#pp $xml;

for my $book ( 0 .. $#{ $xml->{catalog}{book} } ) {
    my $titles = $xml->{catalog}{book}[ $book ]{ titles }{ title };
    for my $title ( 0 .. $#{ $titles } ) {
        my $txt = $titles->[ $title ];
        $txt =~ s[(\d+)]{ $1+1 }e;
        $titles->[ $title ] = $txt;
    }
}

print XMLout( $xml, KeepRoot => 1, NoAttr => 1  );

warn time() - $start;
__END__
C:\test>junk < junk.dat >junk2.dat
3 at C:\test\junk.pl line 22.

    [download]
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    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
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    The start of some sanity?
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