(Looks like the server is not working properly at this moment, it is not taking posts, try again).I cooked a little bit:

while (<STDIN>) {
    chomp;
    if ($_ eq "quit") {
        exit;
    }
    print eval "$_", "\n";
}
[download]

Sample input output would be: (user in put in red, output in blue):
$a=2
2
$a+3
5
($a+5)*2
14
quit