<?php
 $Strings = explode("\n", "1\n2\n3"); // Для проверки
 //$Strings = explode("\n", file_get_contents('strings.txt'));
 $String = $Strings[rand(0, count($Strings) - 1)];
?>
<meta property="og:title" content="<?= $String ?>">
<div id="content"><?= $String ?></div>