#! /usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

use XML::Simple;

my $xml = XMLin('file.xml', ForceArray   => 1,
                            KeyAttr      => [],
                            ForceContent => 1);

my %h;
@h{ map values %{ $_->[0] },
    grep 'ARRAY' eq ref,
    map values %{ $_->[0] },
    values %{ $xml->{tags}[0] }
} = ();
say for keys %h;