if (defined $ARGV[0] and -f $ARGV[0])
{
    if (open(my $fh, $ARGV[0]))
    {
        binmode $fh;
        my $buffer;
        my $len = 0;
        while ($_ = read($fh, $buffer, 1024, $len)) { $len += $_ }
        hexdump($buffer);
    }
}
else
{
    hexdump(<>);
}