One of INPUT_GET, INPUT_POST,
INPUT_COOKIE, INPUT_SERVER,
INPUT_ENV, INPUT_SESSION (not
implemented yet) and INPUT_REQUEST (not
implemented yet).
variable_name
Name of a variable to get.
filter
Filter to apply. Defaults to FILTER_DEFAULT.
options
Associative array of options or bitwise disjunction of flags. If filter
accepts options, flags can be provided in "flags" field of array.
Return Values
Value of the requested variable on success, FALSE if the filter fails,
or NULL if the variable_name
variable is not set.
If the flag FILTER_NULL_ON_FAILURE is used, it
returns FALSE if the variable is not set and NULL if the filter fails.