php中pcntl_exec和exec有什么区别？

Question

我已经阅读了http://us1.php.net/manual/en/function.pcntl-exec.php和http://php.net/manual/en/function.exec.php上的文档，但我可以不能真正说出实际的区别是什么。

Answer 1

The pcntl_exec() function works exactly like the standard (unix-style) exec() function. It differs from the regular PHP exec() function in that the process calling the pcntl_exec() is replaced with the process that gets called. This is the ideal method for creating children

. In a simple example (that does no error checking):

switch (pcntl_fork()) {
  case 0:
    $cmd = "/path/to/command";
    $args = array("arg1", "arg2");
    pcntl_exec($cmd, $args);
    // the child will only reach this point on exec failure,
    // because execution shifts to the pcntl_exec()ed command
    exit(0);
  default:
    break;
}

// parent continues
echo "I am the parent";

Referred from comments here: http://us1.php.net/manual/en/function.pcntl-exec.php