Why doesn't exec(“top”); work on Linux?

Question

I was trying to execute this command

echo exec(\"top\");

and

echo exec(\"/usr/bin/top\");

neither works

Answer 1

It probably works, but exec() doesn't return anything. Read the Manual: exec()

$output = null;
exec('top', $output);
echo $output;

But you have another problem: top doesn't exit by itself. You cannot use it here, because you need to send the interrupt-signal (just realized: q is ok too).

One solution is to make top to stop after one iteration

$output = null;
exec('top -n 1', $output);
var_dump($output);