<?php
 
$string = "There is an URL in the middle of nowhere: **http://w...content-available-to-author-only...e.com/dnvjndjnvjd** and here's another one **http://w...content-available-to-author-only...e.com/ddadadada**";
 
$regex = '~\*{2}(https?://(?:www\.)?(\S+))\*{2}~';
 
$string = preg_replace_callback($regex,
    function($match) {
        return "<a href='{$match[1]}'>" . substr($match[2], 0, 10) . "</a>";
    },
    $string);
 
echo $string;
?>

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