How to actually modify values of an XML file using XML::LibXML

Question

I have an XML file (information.xml). I have to extract element and attribute values from this XML file and insert those element and attribute values into another XML file (build.xml). I have to change the build.xml file by filling the appropriate element values and tags from information.xml file.

I have to use XML::LibXML to do so. I am able to extract the element and attribute values from information.xml. But, I am unable to open and fill those values in build.xml

Example :

information.xml

<info>
  <app version="10.5.10" long_name ="My Application">
    <name> MyApp </name>
    <owner>larry </owner>
    <description> This is my first application</description>
  </app>
</info>

build.xml

<build long_name="" version="">
  <section type="Appdesciption">
    <description> </description>
  </section>
  <section type="Appdetails">
    <app_name> </app_name>
    <owner></owner>
  </section>
</build>

Now, my task is to extract value of owner from information.xml, open build.xml, search for owner tag in build.xml and put the extracted value there.

The Perl script looks like:

#!/usr/bin/perl
use strict;
use warnings;
use XML::LibXML;
my $file1="/root/shubhra/myapp/information.xml";
my $file2="/root/shubhra/myapp/build.xml";

my $parser = XML::LibXML->new();
my $doc = $parser->parse_file($file1);
foreach my $line ($doc->findnodes('//info/app'))
{
    my $owner= $line->findnodes('./owner');  # 1st way
    print "\n",$owner->to_literal,"\n";

    my ($long_name) = $line->findvalue('./@long_name');  # 2nd way
    print "\n $long_name \n";

    my $version = $line->findnodes('@version');
    print "\n",$version->to_literal,"\n";
}

my $parser2 = XML::LibXML->new();
my $doc2 = $parser2->parse_file($file2);
foreach my $line2 ($doc2->findnodes('//build'))
{
    my ($owner2)= $line2->findnodes('./section/owner/text()');

    my ($version2)=$line2->findvalue('./@version');

    print "\n Build.xml already has version : $version2 \n";
    print "\n Build.xml already has owner :",$owner2->to_literal;

    $owner2->setData("Windows Application 2"); # Not changing build.xml
    $line2->setAttribute(q|version|,"60.60.60");  # Not changing build.xml 
    my $changedversion = $line2->getAttribute(q|version|); 
    #superficially changed but didn't changed build.xml content
    print "\n The changed version is : $changedversion";
}

build.xml looks like :

<build long_name="" version="9.10.10">
<section type="Appdesciption">
<description> </description>
</section>
<section type="Appdetails">
<app_name> </app_name>
<owner>shubhra</owner>
</section>
</build>

my $doc3 = XML::LibXML->load_xml(location => $file2, no_blanks => 1);
my $xpath_expression = '/build/section/owner/text()';
my @nodes = $doc3->findnodes( $xpath_expression );
for my $node (@nodes) {
    my $content = $node->toString;
    $content = $owner;
    $node->setData($content);
}
$doc->toFile($file2 . '.new', 1);

What have you tried? Can't you think of any DOM methods that might be useful? Perhaps you want to re-read the documentation on DOM nodes and XML elements. — amon
– amon, Commented Sep 10, 2013 at 7:19
I tried doing so by using findnode and findvalue option. Using findnode, I go to the particular node and using findvalue I extract the output in a variable. But, when i am trying to put that variable value in build.xml, i am unable to change the content. — Shubhra Garg
– Shubhra Garg, Commented Sep 10, 2013 at 7:32
OP, you need to show what you've done so we can help you. I don't see what you've been trying in terms of Perl code for the past 3 days. — Zaid
– Zaid, Commented Sep 10, 2013 at 7:32
Okay.wait. i will add the code here. I am making use of "setData()" to change element value. Do, I need to load the xml to actually change the content of xml file. Also, i need to make use of Xml::LIBXML only, as this is part of my old code. — Shubhra Garg
– Shubhra Garg, Commented Sep 10, 2013 at 7:39
Well, this is like complaining that while (<$fh>) { $_ = 42 } doesn't change the input file. The DOM is not magically tied to a file, it is a seperate in-memory representation. You have to write the document back to the file yourself, e.g. use File::Slurp; write_file "output.xml", { binmode => ':utf8' }, $doc2->toString. — amon
– amon, Commented Sep 10, 2013 at 9:41

ikegami · Accepted Answer · 2023-01-29 07:08:27Z

4

The following fails to find anything (setting $owner2 to undef) since owner has no text:

my ($owner2) = $line2->findnodes('./section/owner/text()');

You want

my ($owner2) = $line2->findnodes('./section/owner');

This entails changing

print "\n Build.xml already has owner :", $owner2->to_literal;

to

print "\n Build.xml already has owner :", $owner2->textContent;

and

$owner2->setData("Windows Application 2");

to

$owner2->removeChildNodes();
$owner2->appendText("Windows Application 2");

You imply you want the following to change build.xml, but it doesn't even mention build.xml:

$line2->setAttribute(q|version|, "60.60.60");

It does modify $doc2, but you'll need to add the following code to modify build.xml too:

$doc2->toFile('build.xml');

edited Jan 29, 2023 at 7:08

answered Sep 10, 2013 at 13:17

ikegami

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14 Comments

Shubhra Garg Over a year ago

Thank you so much for helping and letting me know the chnages. I am new to Libxml module. But, could you please explain by example :---> why you are making use of removeChildNodes() function. What if , if I have "many nodes/elements" with the "same name" are present under one tag. Example : If I have total 3 disk's under main tag disk. Tags look like : <disks> <disk id="1"> </disk> <disk id="2"></disk> <disk id="3"> <disk> </disks>

Shubhra Garg Over a year ago

Could you please explain!

ikegami Over a year ago

Re "why you are making use of removeChildNodes() function.", to remove any existing text node before adding a new one.

ikegami Over a year ago

Re "What if , if I have 'many nodes/elements' with the 'same name'", Are you asking how to extract them? my @disks = $disks->findnodes('disk'); or my @disks = $parent_of_disks->findnodes('disks/disk');

Shubhra Garg Over a year ago

Could you please answer...appendText is not working! -ikegami

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