$re = '/.*?\((\d\d)\)|.*/';
$str = 'C10438 03 EXT-OBLN-ASSN PIC X(05).
03 EXT-OWN-NAME PIC X(40).
';
$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