How can PHP developers ensure that the data retrieved from a URL variable is sanitized and secure?

To ensure that data retrieved from a URL variable is sanitized and secure, PHP developers can use the filter_input function with the FILTER_SANITIZE_STRING filter to sanitize the input. This function filters a variable with a specified filter, in this case, FILTER_SANITIZE_STRING, which removes or encodes any special characters in the input.

$url_variable = filter_input(INPUT_GET, 'url_variable', FILTER_SANITIZE_STRING);