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

<?php
$array = array(
    0 => 100,
    "color" => "red"
);
print_r(array_keys($array));
?>

Output:

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

Example 2 – Using search_value

<?php
$array = array("blue", "red", "green", "blue");
print_r(array_keys($array, "blue"));
?>

Output:

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

Example 3 – Using strict comparison

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

Output:

Array
(
    [0] => color
)