The PHP filter_has_var() function checks whether a variable of a specified input type exists.

The PHP filter_id() function returns filter ID of a specified filter name.

The PHP filter_input() function gets an external variable from insecure sources (e.g., user input) and optionally filters it to validate variables.

The PHP filter_input_array() function gets external variables (e.g. from form input) and optionally filters them.

The PHP filter_list() function returns a list of all the supported filter names.

The PHP filter_var() function filters a variable with the specified filter.

The PHP filter_var_array() function gets multiple variables and optionally filters them.