my %operations = (
  '+' => sub { (shift) + (shift) },
  '-' => sub { (shift) - (shift) },
  '*' => sub { (shift) * (shift) },
  '/' => sub { (shift) / (shift||1) },
);

my ($left,$op,$right) = ...; #wherever you get them from
print exists $operations{$op} ?
    $operations{$op}->($left,$right) :
    "dunno operator '$op'",
"\n";