PHP Filters

The PHP filters is used to sanitize and validate and data coming from insecure sources, like user input.

## PHP Filter Functions
Since PHP 5.2.0, the filter functions are enabled by default. You can use them directly in your code without any further installation.

| Function             | Description                                                         |
|----------------------|---------------------------------------------------------------------|
| filter_has_var()     | Checks if variable of specified type exists                         |
| filter_id()          | Returns the ID number of a specified filter                         |
| filter_input()       | Gets a specific external variable by name and optionally filters it |
| filter_input_array() | Gets multiple external variables and optionally filters them        |
| filter_list()        | Returns an array of all supported filters                           |
| filter_var_array()   | Gets multiple variables and optionally filters them                 |
| filter_var()         | Filters a variable with a specified filter                          |

## PHP Sanitize Filters
The sanitize filters are used to sanitize or clean the user inputs.

| ID                            | Description                   |
|-------------------------------|--------------------------------|
| FILTER_SANITIZE_EMAIL         | Remove all characters except letters, digits and <code>!#$%&amp;'*+-/=?^_`{&#124;}~@.[]</code>          |
| FILTER_SANITIZE_ENCODED       | URL-encode string, optionally strip or encode special characters.               |
| FILTER_SANITIZE_MAGIC_QUOTES  | Apply `addslashes()`.           |
| FILTER_SANITIZE_NUMBER_FLOAT  |  Remove all characters except digits, +- and optionally .,eE    |
| FILTER_SANITIZE_NUMBER_INT    | Remove all characters except digits, plus (+) and minus (-) sign.                    |
| FILTER_SANITIZE_SPECIAL_CHARS | HTML-escape '"&lt;&gt;&amp; and characters with ASCII value less than 32, optionally strip or encode other special characters. |
| FILTER_SANITIZE_STRING        | Strip tags, optionally strip or encode special characters.                         |
| FILTER_SANITIZE_STRIPPED      | Alias of "string" filter.          |
| FILTER_SANITIZE_URL           | Remove all characters except letters, digits and <code>$-_.+!*'(),{}&#124;\\\^~[]`&lt;&gt;#%";/?:@&amp;=</code>                                   |
| FILTER_UNSAFE_RAW             | Do nothing, optionally strip or encode special characters.   |

## Validate Filters
The sanitize filters are used to validate the user inputs.

| ID                      | Description        |
|-------------------------|-----------------|
| FILTER_VALIDATE_BOOLEAN | Returns TRUE for "1", "true", "on" and "yes". Returns FALSE otherwise.                              |
| FILTER_VALIDATE_EMAIL   | Validates value as e-mail.        |
| FILTER_VALIDATE_FLOAT   | Validates value as float.             |
| FILTER_VALIDATE_INT     | Validates value as integer optionally from the specified range.        |
| FILTER_VALIDATE_IP      | Validates value as IP address, optionally only IPv4 or IPv6 or not from private or reserved ranges. |
| FILTER_VALIDATE_REGEXP  | Validates value against regexp, a Perl-compatible regular expression.                               |
| FILTER_VALIDATE_URL     | Validates value as URL, optionally with required components.    |