How to get a node value from xml based on another node value using perl

Question

I have my projects.xml file as below:

<projects>
    <project>
        <id>ID_ABCD1</id>
        <name>ptest1</name>
    </project>
    <project>
        <id>IDB_abcd</id>
        <name>ptest1</name>
        <branch>bnm1</branch>
        <branched_from_id>ID_ABCD1</branched_from_id>
        <branched_from_version>111</branched_from_version>
    </project>
    <project>
        <id>ID_ABCD2</id>
        <name>ptest2</name>
    </project>
    <project>
        <id>IDB_abcd2</id>
        <name>ptest2</name>
        <branch>bnm2</branch>
        <branched_from_id>ID_ABCD2</branched_from_id>
        <branched_from_version>111</branched_from_version>
    </project>
</projects>

In my existing code I am getting project names based on project ID obtained from another file categories.xml.

For each of these project names I have to search is there any branch element for it, and if the element exists then I have to get the corresponding branch name and branched_from_version.

branched_from_id value is the ID of some other project.

#!/usr/bin/env perl

use strict;

use XML::LibXML;
use File::Basename;
use File::Find::Rule;
use XML::Twig;

my $cat_xml  = '/home/Ras/categories.xml';
my $twig     = XML::Twig->parse( $cat_xml );
my $doc      = XML::LibXML->new->parse_file( $cat_xml );

my $proj_xml = '/home/Ras/projects.xml';
my $twigp    = XML::LibXML->new->parse_file( $proj_xml );

my @nodes    = $doc->findnodes( '/categories/category' );

my $catname  = "/home/Ras/category.txt";

open FH, "> $catname" or warn "not able to open catname file";

foreach my $catnode ( @nodes ) {
    my @catn = $catnode->findvalue( '@name' );
    print FH "@catn \n";
}

my @catlist = `cat /home/Ras/category.txt`;

foreach my $cat ( @catlist ) {

    chomp( $cat );
    $cat =~ s/^\s+|\s$//g;

    my $path = "./category[\@name=\"$cat\"]/project";

    foreach my $project ( $twig->findnodes( "$path" ) ) {

        my $projout = $project->text;

        foreach my $projname ( $twigp->findvalue( "/projects/project[id = '$projout']/name" ) ) {

        }
    }
}

In above code $projout contain the ID value of my project.xml file. But those ID value with branch node are not there.

I have name value in $projname. So based on the name value in $projname I need to get the corresponding branch value and branched_from_version value.

Why are you mixing XML::Twig and XML::LibXML? That looks like a road to pain. — Sobrique
– Sobrique, Commented Dec 2, 2016 at 9:54
Can you clarify what the expected inputs and outputs are? Perhaps a minimal reproducible example that we can run, with what the desired output would be? — Sobrique
– Sobrique, Commented Dec 2, 2016 at 9:56
This is a bit of a mess. You create a list of category names from categories.xml and write it to disk; then you read it back and search the same xml file for those category elements! You will need to show categories.xml as well if you want help with this. — Borodin
– Borodin, Commented Dec 2, 2016 at 11:03

Sobrique · Accepted Answer · 2016-12-02 10:04:48Z

It's a bit simplified, but I think you're trying to do something like this:

#!/usr/bin/env perl
use warnings;
use strict;

use XML::Twig;

my $twig = XML::Twig -> parsefile ( 'test.xml' );
my $project = 'ptest2'; 

if ( $twig -> get_xpath("//project/name[string()=\"$project\"]" ) ) {
    print $twig -> get_xpath("//project/name[string()=\"$project\"]",0 ) -> text, " exists\n";
    foreach my $branch ( $twig -> get_xpath("//project/name[string()=\"$project\"]/../branched_from_id/..",0 ) ) {
       print "$project : ", $branch -> first_child_text('branched_from_id'), " => ", $branch -> first_child_text('branched_from_version'),"\n";
    }
}

I've had to cut it down, because I don't have your projects list. But this will use XML::Twigs get_xpath to find a project name - although note, it doesn't differentiate whether it's a branch or not for the first part of the check.

And then pulls out an xpath match based on this of all the branches that 'match'.

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