#!/usr/bin/perl 
use warnings ; # perl5 adn above
use strict ; # always! 
use Data::Dumper;  

my @files ;
my %hashtest;

# load some dummy data
$hashtest{'abc'}{'filename'} = 'fred';
$hashtest{'def'}{'filename'} = 'harry';

# unfold outter has keys
foreach my $key (keys (%hashtest))
{
    # push the file name ont @files. 
    # printing $hashtest{$key}{'filename'} etc would 
    # be apropriate as  well
    push @files, $hashtest{$key}{'filename'} ;
}

print Dumper(\@files);