Online PHP editor | output for nVcHa

<?php $test = '2+3*pi'; // Remove whitespaces $test = preg_replace('/\s+/', '', $test); $number = '(?:\d+(?:[,.]\d+)?|pi|π)'; // What is a number $functions = '(?:sinh?|cosh?|tanh?|abs|acosh?|asinh?|atanh?|exp|log10|deg2rad|rad2deg|sqrt|ceil|floor|round)'; // Allowed PHP functions $operators = '[+\/*\^%-]'; // Allowed math operators $regexp = '/^(('.$number.'|'.$functions.'\s*$(?1)+$|$(?1)+$)(?:'.$operators.'(?2))?)+$/'; // Final regexp, heavily using recursive patterns if (preg_match($regexp, $test)) { $test = preg_replace('!pi|π!', 'pi()', $test); // Replace pi with pi function eval('$result = '.$test.';'); } else { $result = false; }