Listing all the child nodes of document element

Question

I have a very huge XML file and i want to list down all the child nodes for document element. I am using the below code which is working fine but it is taking very long time to process the file and also it is getting data from the document element which is not required:

use XML::Simple;
my $xml = XML::Simple->new();
my $d = $xml->XMLin("sample.xml");
my @arr = keys %$d;
print "@arr\n";

Example XML:

    <?xml version="1.0" encoding="ISO-8859-15"?>
<document version="1.0" createdAt="2017-03-31T11:41:34">
   <TITLE>Computer Parts</TITLE>
   <PART001>
      <ITEM>Motherboard</ITEM>
      <MANUFACTURER>ASUS</MANUFACTURER>
      <MODEL>P3B-F</MODEL>
      <COST> 123.00</COST>
   </PART001>
   <PART002>
      <ITEM>Video Card</ITEM>
      <MANUFACTURER>ATI</MANUFACTURER>
      <MODEL>All-in-Wonder Pro</MODEL>
      <COST> 160.00</COST>
   </PART002>
   <PART003>
      <ITEM>Sound Card</ITEM>
      <MANUFACTURER>Creative Labs</MANUFACTURER>
      <MODEL>Sound Blaster Live</MODEL>
      <COST> 80.00</COST>
   </PART003>
   <PART004>
      <ITEM>14 inch Monitor</ITEM>
      <MANUFACTURER>LG Electronics</MANUFACTURER>
      <MODEL> 995E</MODEL>
      <COST> 290.00</COST>
   </PART004>
</document>

Expected Output: TITLE, PART001, PART002, PART003, PART004

Can anyone please suggest a faster and better way to get the required output?

Answer 1

By using XML::LibXML and XPath.

use 5.014;
use warnings;
use XML::LibXML;

my $file = 'xml';
my $dom = XML::LibXML->load_xml(location => $file);

for my $child ($dom->findnodes( q{//document/*} )) {
    say $child->nodeName();
}

output

TITLE
PART001
PART002
PART003
PART004

or just for the case, if you need only the PARTs

for my $part ($dom->findnodes( q{//*[contains(name(),'PART')]} )) {
    say $part->nodeName();
}

output

PART001
PART002
PART003
PART004

EDIT: Using the pull parser (doesn't loads the whole xml into memory):

use 5.014;
use warnings;
use XML::LibXML::Reader qw(XML_READER_TYPE_ELEMENT);

my $file="xml";    
my $reader = XML::LibXML::Reader->new(location => $file) or die "problem $!";

while($reader->read()) {
        if( $reader->depth == 1 && $reader->nodeType == XML_READER_TYPE_ELEMENT ) {
                say $reader->name;
        }
}

TITLE
PART001
PART002
PART003
PART004

EDIT2

use 5.014;
use warnings;

use XML::LibXML::Reader qw(XML_READER_TYPE_ELEMENT);
my $file="xml";

my $reader = XML::LibXML::Reader->new(location => $file) or die "problem $!";
my $indoc;
while($reader->read()) {
        # sets the flag in youre inside the <document>
        if( $reader->name eq 'document' ) {
                $indoc = $reader->nodeType == XML_READER_TYPE_ELEMENT ? 1 : 0;
        }
        # all nodes with level 1 if they're inside of the <document>
        if( $indoc &&  $reader->depth == 1 && $reader->nodeType == XML_READER_TYPE_ELEMENT ) {
                say $reader->name;
        }
}

Answer 2

You can use XML::Twig which, according to its documentation, is a perl module for processing huge XML documents in tree mode.

Here's an example fitting your use case:

use feature qw(say);
use XML::Twig;

XML::Twig->new(twig_handlers => {
    'document/*' => sub {
        say $_->name; # print out the element name
        $_->purge; # remove the entire element from memory
    }   
})->parsefile('sample.xml');

When used with your sample document, this prints out:

TITLE
PART001
PART002
PART003
PART004

Using a streaming parser might be even faster.