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

PHP provides a powerful set of array handling functions, and array_keys() is one of the most useful. It returns a new array containing all the keys from a given array.

The syntax of array_keys() is:

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

Parameters:

$array : The input array whose keys are to be retrieved.

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

$strict (optional): When true, the comparison uses strict type checking.

Below are three examples demonstrating different use cases.

Example 1 – Indexed array:

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

Output:

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

Example 3 – Multidimensional array (first element keys):

<?php
$students = array(
    array("name" => "Mike", "age" => 20),
    array("name" => "John", "age" => 22),
    array("name" => "Sarah", "age" => 19)
);
$names = array_keys($students[0]);
print_r($names);
?>

Output:

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

These examples show that array_keys() works with indexed, associative, and even multidimensional arrays, making it a versatile tool for retrieving keys in PHP development.

In summary, the array_keys() function is concise, flexible, and highly practical for real‑world backend programming.