$re = '/(?:(SUM|AGV|ABS)\(\{((?:[A-Za-z])+)\}\)|(?:(SUM|AGV|ABS)\(\{((?:[A-Za-z])+)\}\,\{((?:[A-Za-z])+)\}\))|\{((?:[A-Za-z])+)\})(?:(\+|\-|\*|\/)(?:(?:(SUM|AGV|ABS)\(\{((?:[A-Za-z])+)\}\))|(?:(SUM|AGV|ABS)\(\{((?:[A-Za-z])+)\}\,\{((?:[A-Za-z])+)\}\))|(?:\{((?:[A-Za-z])+)\})))*/m';
$str = 'ABS({AbcdefgF},{AbcdefgF})+SUM({AbcdefgF},{A})
SUM({AbcdefgF})+SUM({AbcdefgF})
{AbcdefgF}+{AbcdefgF}-{AbcdefgF}';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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