foreach my $chars (split(//,$input_string)) {
    $hexchars .= sprintf "%x", ord($chars);
}

##</code><code>##

$ perl -le '
$str = qq{test\r\n};
$wrong = join q{}, map { sprintf q{%x}, ord } split m{}, $str;
print $wrong;
$right = join q{}, map { sprintf q{%02x}, ord } split m{}, $str;
print $right;'
74657374da
746573740d0a