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

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

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

Parameters:

$array : The array whose keys you want to retrieve.

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

$strict (optional): When set to true , the comparison is strict (both type and value must match).

Example 1 – retrieving keys from an 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
)

The code creates a simple indexed array, calls array_keys() to obtain its keys, stores them in $keys , and prints the resulting array of indices.

Example 2 – retrieving keys from an associative array:

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

Output:

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

Here the function extracts the names of the students (the keys) from the associative array.

Example 3 – retrieving keys from a multidimensional array (first element):

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

Output:

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

This demonstrates that array_keys() works with multidimensional arrays, returning the keys of the specified inner array.

In summary, the array_keys() function is a concise and flexible tool for obtaining all keys from indexed, associative, or multidimensional arrays in PHP, making it highly useful in everyday development.