sub consume {
    my ($filehandle) = @_;
    my %result;
    while ( defined($_ = <$filehandle>) ) {
        chomp; 
        next unless /dev/;
        ($mount_point, $total_space, $used_space, $free_space) = split;
         $result{$mount_point}{total} = $total_space;
         $result{$mount_point}{used}  = $used_space;
         $result{$mount_point}{free)} = $free_space;
    }
    return %result;
}

##</code><code>##

    # Assume first machine is the more important one and we want to be sure we check
    # all its filesystems. (We can't guarantee we looked at all of the second machine's
    # filesystems because this just uses the same keys as machine 1 to look at machine 2.
    # There might be more filesystems with different names.)
    
    my @unmatched;
    # Section 1: matched on both.
    foreach my $filesystem_name (sort keys %first_machine) {
        print "$filesystem_name: ";
        my $has_differences;
        foreach my $type (qw(total free used)) {
            if (exists $second_machine{$filesystem_name}) {
                # Filesystem mounted on both machines
                my $difference = $first_machine{$filesystem_name}{$type} - $second_machine{$filesystem_name}{$type};
                if ($difference) {
                    print "$type: $difference ";
                    $has_differences = 1;
                }
                print "\n"; # finish the line and output it
                delete $second_machine{$filesystem_name};
            }
            else {
                push @unmatched, "$filesystem_name: ";
                foreach my $kind (qw(total free used)) {
                    $unmatched[-1] .= $first_machine{$unmatched}{$kind} . " ";
                }
                $unmatched[-1] .= "\n";
        }
    }
    # Second section: unmatched on first machine.
    if (@unmatched) {
        print @unmatched;
    }

    # Third section: unmatched on second machine.
    if (keys %second_machine) {
        # unprocessed filesystems on 2 not on 1.
        print "Unmatched filesystems on machine 2:\n";
        foreach my $unmatched (sort keys %second_machine) {
            print "$unmatched ";
            foreach my $kind (qw(total free used)) {
                print $second_machine{$unmatched}{$kind}, " ";
            }
            print "]\n";
        }
    }