$re = '/((?:[^,]*,){10}) /';
$str = 'A0ihO, gIUW4, Kh6Xp, sYAXL, IZvuE, PtQvw, zeSEt, YsCo0, WfzbU, 5TTIz, oKTOO, qaaTK, y4QUd, C4vNY, lDplP, Gjrg8, UHzUT, 32ZcV, c7xgl, 5Lr2H, fDgxt, zFdYO, hohuK, vrNU4, 8oRg5, IYcyl, pblbO, SHhq0, yFjWa, rzYLr, m2AXf, QdhtM, TWpkh, 4499K, 5Bcv8, 0DeqI, 6BdTy, fJgKX, tUZeh, HPso5';
$subst = "\1\n";
$result = preg_replace($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