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

my $userref = ();
$userref->{0}{'hash'}{'name'} = 'joe';
$userref->{0}{'hash'}{'type'} = 'user';
$userref->{1}{'hash'}{'name'} = 'mary';
$userref->{1}{'hash'}{'type'} = 'user';

my $XmlRef = ();

# loop thru all keys in userref
for my $key(sort keys %$userref){

  # the key name
  my $keyname = 'key'.$key;

  my $cnt = scalar keys %{$XmlRef->{$keyname}{'devices'}};

  my $i=0;
  for my $foo(keys %{$userref->{$key}{'hash'}}){
    $XmlRef->{$keyname}{'devices'}{'dev'.$cnt}{'param'}{$foo}{'content'} = [ $userref->{$key}{'hash'}{$foo} ];
    $i+=1;
  }

}

# write XML to file
my $tmpfile = '/tmp/testfile.xml';
my $fh;
open $fh, '>', $tmpfile or die "open($tmpfile): $!\n";
XMLout($XmlRef,
  XMLDecl    => '<?xml version="1.0" encoding="utf-8"?>',
  ContentKey => '-content',
  NoAttr     => 0,
  OutputFile => $fh,
  KeyAttr    => { 'param' => 'id' },
  AttrIndent => 1,
);
close $fh;

##</code><code>##

<?xml version="1.0" encoding="utf-8"?>
<opt>
  <key0>
    <devices>
      <dev0>
        <param id="name">
          <content>joe</content>
        </param>
        <param id="type">
          <content>user</content>
        </param>
      </dev0>
    </devices>
  </key0>
  <key1>
    <devices>
      <dev0>
        <param id="name">
          <content>mary</content>
        </param>
        <param id="type">
          <content>user</content>
        </param>
      </dev0>
    </devices>
  </key1>
</opt>

##</code><code>##

<opt>
  <key0>
    <devices>
      <dev0>
        <param id="name">joe</param>
        <param id="type">user</param>
      </dev0>
    </devices>
  </key0>