C语言 如何正确使用fork、exec、wait
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how to correctly use fork, exec, wait
提问by Collin
The shell i'm writing needs to execute a program given to it by the user. Here's the very shortened simplified version of my program
我正在编写的 shell 需要执行用户提供给它的程序。这是我的程序的非常缩短的简化版本
int main()
{
pid_t pid = getpid(); // this is the parents pid
char *user_input = NULL;
size_t line_sz = 0;
ssize_t line_ct = 0;
line_ct = getline(&user_input, &line_sz, stdin); //so get user input, store in user_input
for (;;)
{
pid_t child_pid = fork(); //fork a duplicate process
pid_t child_ppid = getppid(); //get the child's parent pid
if (child_ppid == pid) //if the current process is a child of the main process
{
exec(); //here I need to execute whatever program was given to user_input
exit(1); //making sure to avoid fork bomb
}
wait(); //so if it's the parent process we need to wait for the child process to finish, right?
}
}
- Have I forked the new process & checked to see if it's a child process correctly
- What exec could I use here for what I'm trying to do? What is the most simple way
- What are my arguments to wait? the documentation I'm looking at isn't helping much
- 我是否分叉了新进程并检查它是否是正确的子进程
- 我可以在这里使用什么 exec 来完成我想要做的事情？最简单的方法是什么
- 我等待的理由是什么？我正在查看的文档没有多大帮助
Assume the user might input something like ls, ps, pwd
假设用户可能会输入诸如 ls、ps、pwd 之类的内容
Thanks.
谢谢。
Edit:
编辑：
const char* hold = strdup(input_line);
char* argv[2];
argv[0] = input_line;
argv[1] = NULL;
char* envp[1];
envp[0] = NULL;
execve(hold, argv, envp);
回答by Kerrek SB
Here's a simple, readable solution:
这是一个简单易读的解决方案：
pid_t parent = getpid();
pid_t pid = fork();
if (pid == -1)
{
// error, failed to fork()
}
else if (pid > 0)
{
int status;
waitpid(pid, &status, 0);
}
else
{
// we are the child
execve(...);
_exit(EXIT_FAILURE); // exec never returns
}
The child can use the stored value parentif it needs to know the parent's PID (though I don't in this example). The parent simply waits for the child to finish. Effectively, the child runs "synchronously" inside the parent, and there is no parallelism. The parent can query statusto see in what manner the child exited (successfully, unsuccessfully, or with a signal).
如果孩子parent需要知道父母的 PID（虽然我在这个例子中没有），它可以使用存储的值。父母只是等待孩子完成。实际上，子进程在父进程内部“同步”运行，没有并行性。父级可以查询status以查看子级退出的方式（成功、不成功或有信号）。
