Using PHP array_keys() Function: Syntax, Parameters, and Practical Examples

In PHP there are many powerful array handling functions, and array_keys() is a very useful function that returns a new array containing all the key names of a given array.

The syntax of array_keys() is:

array_keys ( array $array [, mixed $search_value = null [, bool $strict = false ]] ) : array

Parameters:

$array : The array from which to retrieve the keys.

$search_value (optional): If provided, only keys whose corresponding values are equal to $search_value are returned.

$strict (optional): When set to true , a strict comparison (both type and value) is used.

Below are several examples of using array_keys() :

Example 1 – Indexed array:

<?php
// Create an array
$fruits = array("apple", "banana", "orange", "apple", "grape");
// Get all keys
$keys = array_keys($fruits);
// Print result
print_r($keys);
?>

Output:

Array
(
    [0] => 0
    [1] => 1
    [2] => 2
    [3] => 3
    [4] => 4
)

Example 2 – Associative array:

<?php
// Create an associative array
$student_scores = array("Mike" => 85, "John" => 92, "Sarah" => 78);
// Get all keys
$keys = array_keys($student_scores);
// Print result
print_r($keys);
?>

Output:

Array
(
    [0] => Mike
    [1] => John
    [2] => Sarah
)

Example 3 – Multidimensional array:

<?php
// Create a multidimensional array
$students = array(
    array("name" => "Mike", "age" => 20),
    array("name" => "John", "age" => 22),
    array("name" => "Sarah", "age" => 19)
);
// Get keys of the first sub‑array
$names = array_keys($students[0]);
// Print result
print_r($names);
?>

Output:

Array
(
    [0] => name
    [1] => age
)

These examples show that array_keys() can conveniently retrieve all keys from indexed arrays, associative arrays, and even multidimensional arrays, making it a versatile tool in PHP development.

In summary, the array_keys() function is a concise and flexible way to obtain the keys of any array in PHP, and its simplicity and power make it highly practical for real‑world coding tasks.