Command launch process with watching the possible error at launching stage.

spawn.php

function spawn($command_line, $dir)
{
    $descriptorspec = [
        0 => [ "pipe", "r" ], // stdin
        1 => [ "pipe", "w" ], // stdout
        2 => [ "pipe", "w" ], // stderr
    ];

    $process = proc_open($command_line, $descriptorspec, $pipes, $dir);
    if (!is_resource($process)) {
        return null;
    }
    
    stream_set_blocking($pipes[2], 0); // set non-blocking mode for stderr
    
    usleep(10000); // wait for 10ms. this dirty hacking is enough for this application
    $ps = proc_get_status($process);
    if (!$ps["running"]) {
        return null; // proccess could not survive
    }

    return [ $process, $pipes ];
}