如何从PHP调用Linux dup2？

不幸的是,我发现执行外部程序的所有解决方案都不合适,所以我使用自己的实现,在pcntl_fork之后是pcntl_exec.

但是现在我需要将执行程序的stderr / stdout重定向到某个文件中.很明显,我应该在pcntl_fork之后使用某种dup2 Linux调用,但我在PHP中看到的唯一的dup2是eio_dup2,看起来它不是常规流(如stderr / stdout),而是一些异步流.

如何从PHP调用dup2或如何在没有它的情况下重定向std *？

同样的问题(但没有细节)没有答案：How do I invoke a dup2() syscall from PHP ?

解决方法:

这是一种不需要dup2的方法.它基于this answer.

$pid = pcntl_fork();

switch($pid) {

    case 0:
        // Standard streams (stdin, stdout, stderr) are inherited from
        // parent to child process. We need to close and re-open stdout 
        // before calling pcntl_exec()

        // Close STDOUT
        fclose(STDOUT);

        // Open a new file descriptor. It will be stdout since 
        // stdout has been closed before and 1 is the lowest free
        // file descriptor
        $new_stdout = fopen("test.out", "w");

        // Now exec the child. It's output goes to test.out
        pcntl_exec('/bin/ls');

        // If `pcntl_exec()` succeeds we should not enter this line. However,
        // since we have omitted error checking (see below) it is a good idea
        // to keep the break statement
        break; 

    case -1: 
        echo "error:fork()\n";
        exit(1);

    default:
        echo "Started child $pid\n";
}

为简洁起见,省略了错误处理.但请记住,在系统编程中应该仔细处理任何函数返回值.