use Symfony\Component\Process\Process;

$process = new Process('ls -lsa');

// the same works when using start instead of run
$process->run(function ($type, $data) {
    if (Process::ERR == $type) {
        // $data was sent to the error output
    } else {
        // $data was sent to the standard output
    }
});

use Symfony\Component\Process\Process;

$processes = array();
$processes[] = new Process('ls -lsa');
$processes[] = new Process('ps waux');

while (count($processes) > 0) {
     foreach ($processes as $i => $process) {
         if (!$process->isStarted()) {
             echo "Process starts\n";

             $process->start();

             continue;
         }

         echo $process->getIncrementalOutput();
         echo $process->getIncrementalErrorOutput();

         if (!$process->isRunning()) {
             echo "Process stopped\n";

             unset($processes[$i]);
         }
     }

     sleep(1);
}

use Symfony\Component\Process\ProcessBuilder;

if (!$process->isRunning()) {
    if (!$process->isSuccessful()) {
        $cloned = $process->restart();

        // ...
    }
}

$process->isSuccessful();
$process->hasBeenSignaled();
$process->hasBeenStopped();
$process->isRunning();

// new in 2.2
$process->isStarted();
$process->isTerminated();

if (!$process->isRunning()) {
    if ($process->isStarted() && !$process->isSuccessful()) {
        $cloned = $process->restart();

        // ...
    }
}