PHP filters are used to validate and sanitize external input.
Validating data is determine if the data is in proper form.
Sanitizing data is remove any illegal character from the data.
The PHP filter extension has many of the functions needed for checking user input, and is designed to make data validation easier and quicker.
The filter_list() function can be used to list what the PHP filter extension offers
<table>
<tr>
<td>Filter Name</td>
<td>Filter ID</td>
</tr>
<?php
foreach(filter_list() as $id => $filter){
echo '<tr><td>' .$filter .'</td><td>' .filter_id($filter) . '</td></tr>';
}
?>
</table>
Many web application recieve external input.External input/data can be:
User input from a form
Cookies
Web Services data
Server variables
Database query results
The filter_var() function both validate and sanitize data.
The filter_var() function filters a single variable with a specified filter.It takes two pieces of data:
- The Variable you want to check
- The type of check to use
The following example uses the filter_var() funcion to remove all HTML tags from a string:
<?php
$str = "<h1>Hello World</h1>";
$newStr = filter_var($str, FILTER_SANITIZE_STRING);
echo $newStr; //Hello World
?>
The following example uses the filter_var() function to check if the variable $int is an integer.
<?php
$int = 100;
// if $int was set to 0, the function will return "Integer is not valid"
// filter_var($int, FILTER_VALIDATE_INT) ===0 it will work when you set 0 to $int
if(!filter_var($int, FILTER_VALIDATE_INT) === false){
echo("Integer is valid");
}else{
echo("Integer is not valid");
}
?>
The following example uses the filter_var() function to check if the variable $ip is a valid IP address
<?php
$ip = "127.0.0.1";
if(!filter_var(FILTER_VALIDATE_IP) === false){
echo("$ip is a valid IP address");
}else{
echo("$ip is not a valid IP address");
}
?>
The following example uses the filter_var() function to first remove all illegal characters from the $email variable, then check if it is a valid email address
<?php
$email = "john.doe@example.com";
//remove all illegal characters from email
$email = filter_var($email, FILTER_SANITIZE_EMAIL);
// validate e-mail
if(!filter_var($email, FILTER_VALIDATE_EMAIL) === false){
echo("$email is a valid email address");
}else{
echo("$email is not a valid email address");
}
?>
The following example uses the filter_var() function to first remove all illegal characters from a URL, then check if $url is a valid URL
<?php
$url = "http://www.w3schools.com";
//remove all illegal characters from a url
$url = filter_var($url, FILTER_SANITIZE_URL);
// validate url
if(!filter_var($url, FILTET_VALIDATE_URL) === false){
echo("$url is a valid URL");
}else{
echo("$url is not a valid URL");
}
?>
The following example uses the filter_var() function to check if a variable is both of type INT, and between 1 and 200
<?php
$int = 122;
$min = 1;
$max = 200;
if(filter_var($int, FILTER_VALIDATE_INT, array("options" => array("min_range" => $min, "max_range" => $max))) === false){
echo("Variable value is not within the legal range");
}else{
echo("Variable value is within the legal range");
}
?>
The following example uses the filter_var() function to checkt if the variable $ip is a valid IPv6 address:
<?php
$ip = "2001:0db8:85a3:08d3:1319:8a2e:0370:7334";
if(!filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6) === false){
echo("$ip is a valid IPv6 address");
}else{
echo("$ip is not a valid IPv6 address");
}
?>
The following example uses the filter_var() function to check if the variable $url is a URL with a querystring:
<?php
$url = "http://www.w3schools.com";
if(!filter_var($url, FILTER_VALIDATE_URL, FILTER_FLAG_QUERY_REQUIRED) === false){
echo("$url is a valid URL");
}else{
echo($url is not a valid URL);
}
?>
The following example uses the filter_var() function to sanitize a string.It will both remove all HTML tags, and all characters with ASCII value > 127, from the string:
<?php
$str = "<h1>Hello WorldØÅ</h1>";
$newStr = filter_var($str, FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_HIGH);
echo $newStr;
?>