At a high level, XML::Simple contains two main functions.

• XMLin - store XML in a variable
• XMLout - write an XML file

XMLin

In this example, <p>Hello World</p> is store in a variable named $xml.

#!/usr/bin/perl
use strict;
use warnings;
use XML::Simple;

my $xml= XMLin("<p>Hello World</p>");

XMLout

XMLout is almost always used after XMLin. In this example, XMLin is used to store <p>Hello World</p> in a variable named $xml and then XMLout is used to store the XML in a file named bar.xml.

#!/usr/bin/perl
use strict;
use warnings;
use XML::Simple;

my $xml= XMLin("<p>Hello World</p>");
XMLout($xml, OutputFile => "bar.xml");

In this example, bar.xml would contain something like this. Notice that the <p> tag is now <opt>. More on this in a moment.

<opt>Hello World</opt>

Keys

XML:Simple can be used to do something with keys (name). In this example, "name" will be printed.

#!/usr/bin/perl
use strict;
use warnings;
use XML::Simple;

my $xml = XMLin("example.xml");

foreach my $key (keys %{$xml}) {
  print "$key\n";
}

Values

XML:Simple can be used to do something with values (Bugs Bunny). In this example, "Bugs Bunny" will be printed.

#!/usr/bin/perl
use strict;
use warnings;
use XML::Simple;

my $xml = XMLin("example.xml");

print $xml->{'name'}->{'content'};

Attributes

XML:Simple can be used to do something with attributes (role="main"). In this example, "main" will be printed.

#!/usr/bin/perl
use strict;
use warnings;
use XML::Simple;

my $xml = XMLin("example.xml");

print $xml->{'name'}->{'role'};

Data::Dumper

Data::Dumper can be used to understand how XML::Simple is interpreting the XML. Here is an example of how to use Data::Dumper.

#!/usr/bin/perl
use strict;
use warnings;
use XML::Simple;
use Data::Dumper;

my $xml= XMLin("example.xml");
print Dumper $xml;

Which will produce the following.

• "name" is the root key
• "content" and "role" are child keys below the root key
• "Bugs Bunny" is a value of the "content" key
• "main" is a value of the "role" key 
• Data inside of { } is interpreted as a hash

$VAR1 = {
          'name' => {
                     'content' => 'Bugs Bunny',
                     'role' => 'main'
               }
        };

Let's consider this XML.

<acme>
  <name role="main">Bugs Bunny</character>
  <name role="support">Elmer Fudd</character>
</acme>

Data::Dumper now has the [ ] characters. Data inside of [ ] is interpreted as an array.

$VAR1 = {
          'name' => [
                    {
                     'content' => 'Bugs Bunny',
                     'role' => 'main'
                    },
                     'content' => 'Elmer Fudd',
                     'role' => 'support'
                    }
                  ]
        };

Now, the following would . . .

print $xml->{'name'}->{'content}';

. . . return the following stderr, because $xml->name->content points to both Bugs Bunny and Elmer Fudd.

Not a HASH reference

Hash

Data is considered a hash when the key contains a single piece of data, like this.

$xml->name->content = Bugs Bunny

Array

Data is considered an array when there are two or more identical keys, like this.

$xml->name->content = Bugs Bunny
$xml->name->content = Elmer Fudd