array_keysPHP ManualPrevNextarray_keysarray_keys -- Return all the keys of an arrayDescriptionarray array_keys(array input, mixed [search_value] ); array_keys() returns the keys, numeric and string, from the input array. If the optional search_value is specified, then only the keys for that value are returned. Otherwise, all the keys from the input are returned. Example 1. array_keys() example 1  2 $array = array(0 => 100, "color" => "red"); 3 array_keys ($array); // returns array (0, "color") 4  5 $array = array(1, 100, 2, 100); 6 array_keys ($array, 100); // returns array (0, 2) 7  See also array_values(). Note: This function was added in PHP 4.0. PrevHomeNextarray_flipUparray_merge