popen（）完成替代 [英] popen() alternative

问题描述

我的问题是一个延伸：的popen创建一个额外的sh进程

My question is extension of this one: popen creates an extra sh process

动机：

1）我的程序需要创建一个孩子做哪些<$​​ C $ C>尾上的文件。我需要处理由线路输出线。这就是为什么我使用的popen ，因为它返回FILE *。我可以很容易地获取一行，做我需要做的，并打印出来。

1) My program need to create a child which does tail on a file. I need to process the output line by line. That is why I am using popen because it returns FILE *. I can easily fetch single line, do what I need to do and print it.

用popen这一个问题是，你不（在我的情况tail命令）获得孩子的PID。

One problem with popen is that you do not get pid of child (tail command in my case).

2）我的计划应其子之前不会退出完成。所以，我需要做的等;但没有PID，我不能这样做。

2) My program should not exit before its child is done. So I need to do wait; but without pid, I cannot do it.

我如何能实现这两个目标？

How can I achieve both the goals?

一个可能的（组装机）的解决方案：做execvp（尾-f文件> TMPFILE）和继续读那TMPFILE。我不知道该解决方案有多好，虽然。

A possible (kludge) solution: do execvp("tail -f file > tmpfile") and the keep reading that tmpfile. I am not sure how good this solution is, though.

推荐答案

你为什么不使用管/叉/ exec方法？

Why aren't you using pipe/fork/exec method?

pid_t pid = 0;
int pipefd[2];
FILE* output;
char line[256];
int status;

pipe(pipefd); //create a pipe
pid = fork(); //span a child process
if (pid == 0)
{
// Child. Let's redirect its standard output to our pipe and replace process with tail
 close(pipefd[0]);
 dup2(pipefd[1], STDOUT_FILENO);
 dup2(pipefd[1], STDERR_FILENO);
 execl("/usr/bin/tail", "/usr/bin/tail", "-f", "path/to/your/file", (char*) NULL);
}

//Only parent gets here. Listen to what the tail says
close(pipefd[1]);
output = fdopen(pipefd[0], "r");

while(fgets(line, sizeof(line), output)) //listen to what tail writes to its standard output
{
//if you need to kill the tail application, just kill it:
  if(something_goes_wrong)
    kill(pid, SIGKILL);
}

//or wait for the child process to terminate
waitpid(pid, &status, 0);

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