PHP Process class

Process.php

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<?php
/**
 * @compability: Linux only. (Windows does not work).
 * @author: Alexander Jank <himself@alexanderjank.de>
 */
class Process{
    private $pid;
    private $command;
    private $cmdHash;
    public $output = "";

    public function __construct($cl=false){
        if ($cl != false){
            $this->command = $cl;
            $this->cmdHash = substr(md5($cl), 0, 5);
            $this->runCom();
        }
    }
    private function runCom(){
        $command = 'nohup '.$this->command.' > /tmp/nohup-'. $this->cmdHash .' 2>&1 & echo $!';
        exec($command ,$op);
        $this->pid = (int) $op[0];
        var_dump($op);
    }

    public function setPid($pid){
        $this->pid = $pid;
    }

    public function getPid(){
        return $this->pid;
    }

    public function status(){
        $command = 'ps -p '.$this->pid;
        exec($command,$op);
        if (!isset($op[1]))return false;
        else return true;
    }

    public function start(){
        if ($this->command != '')$this->runCom();
        else return true;
    }

    public function stop(){
        $command = 'kill '.$this->pid;
        exec($command);
        $this->readOutput();
        if ($this->status() == false)return true;
        else return false;
    }

    public function readOutput() {
        $this->output = file_get_contents('/tmp/nohup-'. $this->cmdHash);
        return $this->output;
    }
}

// Usage:
$ping = new Process("ping 8.8.8.8");
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