Execute shell command with timeout and converting stderr to Exception if any

execute.php

<?php

    /**
    * @param int $timeout - max process execution time in seconds until it is terminated
    **/
    function execute($cmd, $stdin = null, $timeout = 600)
    {
        $this->log->debug("executing: " . $cmd . " ". $stdin);
        $cmd = str_replace("\n", "", $cmd);
        $cmd = str_replace("\r", "", $cmd);
        $descriptorspec = array(
            0 => array("pipe", "r"),  // stdin is a pipe that the child will read from
            1 => array("pipe", "w"),  // stdout is a pipe that the child will write to
            2 => array("pipe", "w"),  // stderr is a pipe that the child will write to
        );
        $pipes = array();

        $timeout += time();

        $process = proc_open($cmd, $descriptorspec, $pipes);

        if (!is_resource($process)) {
            throw new Exception('Invalid resource', 1011);
        }

        $output = '';
        $error = '';

        if($stdin) {
            // 0 => writeable handle connected to child stdin
            fwrite($pipes[0], $stdin);
        }
        fclose($pipes[0]);

        do {
            $write = null;
            $exceptions = null;
            $timeleft = $timeout - time();

            if ($timeleft <= 0) {
                proc_terminate($process);
                throw new Exception("command timeout", 1012);
            }

            $read = array($pipes[1],$pipes[2]);
            stream_select($read, $write, $exceptions, $timeleft);

            if (!empty($read)) {
                $output .= fread($pipes[1], 1024);
                $error .= fread($pipes[2], 1024);
            }

            $output_exists = (!feof($pipes[1]) || !feof($pipes[2]));
        } while ($output_exists && $timeleft > 0);

        if ($timeleft <= 0) {
            proc_terminate($process);
            throw new Exception("command timeout", 1013);
        }

        fclose($pipes[1]);
        fclose($pipes[2]);

        proc_close($process);

        if($error) {
            throw new Exception($error, 1012);
        }

        return $output;
    }