php中怎样实现对用户输入的安全检查

function clean_value($val) {
if ($val == "")
{
return "";
}
$val = trim($val);
$val = str_replace("", "*", $val);
$val = str_replace( " " , " " , $val );
$val = str_replace( "&" , "&" , $val );
$val = str_replace( "

" , "-->" , $val );
$val = preg_replace( "/

1<script "="" "&#60;script"="" $val="str_replace(" );="" ,="" i"=""></script>