$re = '@^.*/(abc\d{2})(?:/.*)?$@m';
$str = '/path/path/path/abc22/path/path
/apath/apath/paath/abc11/something/path';
$subst = "\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