I've a ProcessUtil class in my project that does two things.

1. Throw an Exception for exit codes !=0 and return process output instead of the exit code:

    public static function runOrThrow(Process $process) {
        $process->run();

        if($process->isSuccessful()) return $process->getOutput();
        else throw new \Exception(self::formatErrorOutput($process));
    }

It would be nice, if this logic could be provided by the Process component. I expect it to be a common usecase. But I see how integrating this might grow the Process class. It might make sense to think about splitting the definition of a Process from the strategy how a Process should be run. The current Process class already implements two strategies:

• run the process synchronously and return the exit code, don't throw
• run the process asynchrounously, don't throw

1. The second thing my ProcessUtil class does is formatting an error string for the Exception:

    public static function formatErrorOutput(Process $process) {
        return sprintf("Error code %d while running command line:\n%s\nstderr:\n%s\nstdout:\n%s",
            $process->getExitCode(),
            $process->getCommandLine(),
            $process->getErrorOutput(),
            $process->getOutput()
        );
    }