PHP filter_id Function: How to Retrieve PHP Filter IDs

Before PHP 5.2, there was no built-in filter extension in PHP. You had to manually handle and sanitize input. PHP 5.2 added a filter system, and filter_id() was introduced to map filter names to their numeric IDs.

In this article, you will learn how to get filter IDs by examples. Let’s get started.

What is filter_id()?

filter_id() returns the filter ID for a given filter name. It helps when you use PHP’s filter system. It converts a filter’s name like “email” into a numeric ID such as 517.

Here is its syntax:

filter_id(string $filter_name)

• $filter_name: A string like “int”, “email”, or “string”.
• Returns: The numeric ID as an integer.
• Returns false if the name is not valid.

Here is a quick example:

echo filter_id("email"); 

The output:

517

This helps when you store or compare filters as IDs.

So, why use it?

• Use filter_id() when your code works with filters stored in variables. It lets you pass numeric IDs to filtering functions instead of hardcoding names.
• PHP assigns specific numeric values to filters and filter_id() helps retrieve them.

Let’s move on to the following section to understand how to use filter_id() with filter_var() and filter_input().

Use filter_id() with filter_var() and filter_input()

The filter_var() function filters a variable with a specific filter. Instead of using a filter name, you can pass its ID with filter_id().

Example:

$email = "user@example.com";
$filter = filter_id("email");  

if (filter_var($email, $filter)) {
    echo "Valid email";
} else {
    echo "Invalid email";
}

Output:

Valid email

Here:

• You won’t need to update your code manually if the filter name changes in future PHP versions.
• Helps when filter names are stored in variables.

filter_input() retrieves and filters external variables (e.g., from $_GET, $_POST). You can use filter_id() to dynamically specify the filter.

Here is an example:

First, you need to pass the name variable as a param to the URL like this:

localhost/script.php?name=Jasmeen%20Albert

The %20 represents the space between the words in a URL.

Here is the code in script.php page

$filter = filter_id("string"); 
$name = filter_input(INPUT_GET, "name", $filter);

if ($name !== null && $name !== false) {
    echo "Sanitized name: " . $name;
} else {
    echo "Invalid input";
}

This will show you the following output:

Jasmeen Albert

• It helps when your code uses different filters based on user input or settings.
• Useful when filters are stored in variables and need to be applied conditionally.

Wrapping Up

In this article, you learned how to use filter_id() with filter_var() and filter_input() to dynamically validate and sanitize data in PHP.

Here is a quick recap:

• filter_id() converts a filter name into its numeric ID.
• It makes filtering more dynamic and adaptable.
• Works well with filter_var() for validating and sanitizing variables.
• Helps filter_input() fetch and sanitize user input dynamically.

echo filter_id("email");  
// Output: 517

$email = "user@example.com";
$filter = filter_id("email");

if (filter_var($email, $filter)) {
    echo "Valid email";
} else {
    echo "Invalid email";
}

$filter = filter_id("string"); 
$name = filter_input(INPUT_GET, "name", $filter);

if ($name !== null && $name !== false) {
    echo "Sanitized name: " . $name;
} else {
    echo "Invalid input";
}

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