Parsing XML with Perl

Question 1

The easiest way to extract information from XML documents with XML::LibXML is to use the find family of methods. These methods use an XPath expression to select nodes and values from the document. The following script extracts the data you need:

use XML::LibXML;

my $doc = XML::LibXML->load_xml(location => 'so.xml');

for my $entry ($doc->findnodes('//entry')) {
    my $name = $entry->getAttribute('name');
    my $role = $entry->findvalue(
        'local-name(permissions/role-based/*[.="yes"])'
    );
    print("$name;$role\n");
}

It prints

asd;superuser
fgh;superuser
jkl;superreader

I used the local-name XPath function to get the name of the role element.

Note that you might want to use Text::CSV to create CSV files in a more robust way.

Question 2

Another solution with a different module, XML::Twig:

#!/usr/bin/env perl

use warnings;
use strict;
use XML::Twig;

my ($name, $role);

my $twig = XML::Twig->new(
    twig_handlers => {
        'entry' => sub { 
            $name = $_->att('name');
            if ( defined $name && defined $role ) { 
                printf qq|%s;%s\n|, $name, $role;
            }   
            map { undef $_ } ($name, $role);
        },  
        'role-based' => sub { $role = $_->first_child->tag },
    },  
)->parsefile( shift );

Run it like:

perl script.pl xmlfile

That yields:

asd;superuser
fgh;superuser
jkl;superreader

Question 3

Using XML::Rules:

use XML::Rules;

print "name is_superuser is_superreader\n";
my @rules = (
  entry => sub {
    my $entry = $_[1];
    $_ ||= 'no' for @$entry{qw(superuser superreader)};
    print "$entry->{name} $entry->{superuser} $entry->{superreader}\n";
  },
  'permissions,role-based' => 'pass no content',
  'superuser,superreader' => 'content',
  _default => undef,
);

my $p = XML::Rules->new(rules => \@rules);
my $s = $p->parse(doc());

sub doc {
return <<XML;
<users>
   <entry name="asd">
       <permissions>
            <role-based>
                <superuser>yes</superuser>
            </role-based>
       </permissions>
   </entry>
   <entry name="fgh">
       <permissions>
            <role-based>
                <superuser>yes</superuser>
            </role-based>
       </permissions>
       <authentication-profile>RSA Two-Factor</authentication-profile>
   </entry>
   <entry name="jkl">
       <permissions>
            <role-based>
                <superreader>yes</superreader>
            </role-based>
       </permissions>
       <authentication-profile>RSA Two-Factor</authentication-profile>
   </entry>
</users>
XML
}

Or an optional set of rules assuming all content is 'yes' (and some other assumptions) for your key fields:

my $name;
my @rules = (
  '^entry' => sub {
    $name = $_[1]->{name};
  },
  'superuser,superreader' => sub {
    print "$name,$_[0]\n";
  },
  _default => undef,
);

Question 4

I like using XML::Simple for projects like this.

For example:

use XML::Simple;

my $su = $ARGV[0];
die unless (-e $su);

my $su_xml = XMLin($su, ForceArray => [ 'entry' ]);
my $suref = $su_xml->{entry};

foreach my $key (keys %{$suref}) {
    $rb = ${$suref}{$key}->{permissions}->{'role-based'};
    foreach my $rbkey (keys %{$rb}) {
        print "$key\t$rbkey\t${$rb}{$rbkey}\n";
    }
}

prints:

fgh     superuser       yes
asd     superuser       yes
jkl     superreader     yes