<?php
$file_path = 'example.txt';

$file_content = file_get_contents($file_path, NULL, NULL, 0, 1000);

$encoding = mb_detect_encoding($file_content, 'UTF-8', true);

if ($encoding === 'UTF-8') {
    echo "The file is encoded in UTF-8.";
} else {
    echo "The file is not encoded in UTF-8.";
}
?>