Question

I have tried many different combinations of code using the eval command. However my answer is always blank. Here is a simple one i tried.

$equation = "18 - (18 * 2) - 1";
$var = eval($equation);
echo "answer: " . $var;

I understand this does not need the eval code, but the real code I am working on does. It just always shows up blank.

Answer 1

Solution

Add return inside the evaluated statement, otherwise the eval() won’t know what to return:

$equation = '2 + 2 * 2';
$var = eval("return $equation;");

Proof, that the above works: http://ideone.com/bTtIH

About superiority of return vs. setting variable

More from the documentation of eval():

eval() returns NULL unless return is called in the evaluated code, in which case the value passed to return is returned.

In other words: there is no need to pollute the namespace, you can get what you want directly from what eval() returns.