array_keys() – Returns All or Selected Keys of an Array (PHP)

The array_keys() function in PHP returns the keys of an array, which can be either numeric or string.

If the optional search_value parameter is supplied, only the keys whose corresponding values match search_value are returned; otherwise all keys are returned. The optional strict boolean determines whether the comparison uses strict identity ( === ).

Parameters

input (array): The array from which to retrieve keys.

search_value (mixed, optional): The value to search for; only keys of elements equal to this value are returned.

strict (bool, optional): When true , the comparison is strict ( === ).

Return value

Returns an array containing the keys from input that meet the criteria.

Example 1 – Basic usage

100,
    "color" => "red"
);
print_r(array_keys($array));
?>

Output:

Array
(
    [0] => 0
    [1] => color
)

Example 2 – Using search_value

Output:

Array
(
    [0] => 0
    [1] => 2
)

Example 3 – Using strict comparison

array("blue", "red", "green"),
    "size" => array("small", "medium", "large")
);
print_r(array_keys($array, "blue", true));
?>

Output:

Array
(
    [0] => color
)