How can you optimize the performance of a PHP script that involves executing shell commands?

To optimize the performance of a PHP script that involves executing shell commands, you can use the PHP `exec()` function instead of `shell_exec()` as it is more efficient for executing commands. Additionally, you should ensure that the commands being executed are necessary and efficient to reduce unnecessary overhead. Lastly, consider caching the results of the shell commands if they are being executed frequently to avoid repeated processing.

// Example PHP code snippet using exec() function to optimize performance
$command = "ls -l";
$output = exec($command);
echo $output;