I need to run a shell command in PHP and capture STDOUT and STDERR separately. This function lets you run a command and returns a hash with the various components and outputs.

function run_cmd($cmd) {
    $start   = hrtime(true);
    $cmd     = escapeshellcmd($cmd);
    $process = proc_open($cmd, [
        1 => ['pipe', 'w'], // STDOUT
        2 => ['pipe', 'w'], // STDERR
    ], $pipes);

    if (!is_resource($process)) { return []; }

    $stdout = stream_get_contents($pipes[1]);
    fclose($pipes[1]);
    $stderr = stream_get_contents($pipes[2]);
    fclose($pipes[2]);
    $exit   = proc_close($process);

    $ret = [
        'exit_code' => $exit,
        'stdout'    => trim($stdout),
        'stderr'    => trim($stderr),
        'cmd'       => $cmd,
        'exec_ms'   => (hrtime(true) - $start) / 1000000,
    ];

    return $ret;
}