$re = '/([^,]+)/m';
$str = '1.jpg,2.jpg,3.jpg,4.jpg,5.jpg,6.jpg,7.jpg,8.jpg,9.jpg,10.jpg,11.jpg,12.jpg,13.jpg,14.jpg,15.jpg,16.jpg,17.jpg,18.jpg,19.jpg,20.jpg,21.jpg,22.jpg,23.jpg,24.jpg,25.jpg,26.jpg,27.jpg,28.jpg,29.jpg,30.jpg,31.jpg,32.jpg,33.jpg,34.jpg,35.jpg,36.jpg,37.jpg,38.jpg,39.jpg,40.jpg,41.jpg,42.jpg,43.jpg,44.jpg,45.jpg,46.jpg,47.jpg,48.jpg,49.jpg,50.jpg,51.jpg,52.jpg,53.jpg,54.jpg,55.jpg,56.jpg,57.jpg,58.jpg,59.jpg,60.jpg';
$subst = "mysite.com/tripoli/$1";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php