The PHP natcasesort() function sorts an array by using a “natural order” (2 is less than the number 10) algorithm.

This function is case-insensitive. The values keep their original keys.

<?php
$files = array('file15.txt', 'File11.txt', 'file1.txt', 'File44.txt', 'file4.txt');

natcasesort($files);

echo '<pre>';
print_r($files);
echo '</pre>';
?>

Array
(
    [2] => file1.txt
    [4] => file4.txt
    [1] => File11.txt
    [0] => file15.txt
    [3] => File44.txt
)

natcasesort(array)