title: PHP exec() vs system() vs passthru()
body: <p>What are the differences?</p>
  
  <p>Is there a specific situation or reason for each function? If yes, can you give some examples of those situations?</p>
  
  <p>PHP.net says that they are used to execute external programs. <a href="http://php.net/manual/en/function.exec.php" rel="noreferrer">see reference</a>
  From the examples I see, I don't see any obvious difference.</p>
  
  <p>If I were to simply run a script (bash or python), which function do you recommend me to use?</p>