如何终止子进程中的程序？

Question

I am trying to terminate my program which takes a line that is full of commands from a file and then process each command using execvp

However,Whenever I encounter quit , I want to immediately exit processing the commands and ignore all other commands that are coming after it.

I tried to do this the following way using exit()

for(int i =0;i < numOfCommands;i++)
{
    childPid = fork();
    if(childPid == 0)
    {
        if(execvp(commands[i].cmd[0],commands[i].cmd) == -1)
         {
            /*if(strcmp(commands[i].cmd[0],"quit"))
            {
                done = true;
                return;
            }*/

            if(strcmp(commands[i].cmd[0],"quit")==0)
            {
                printf("Quit command found ! \n Quitting .");
                done = true;
                //return;
                 exit(0);


            }
            printf("Command %s is unknown \n", commands[i].cmd[0]);

        }
    }
    else 
    {
                    //parent process
        wait(&child_status);
    }
  }
}

And this happens inside of the child process, after forking of course. But the problem is that my program keeps processing the remaining commands that comes after quit before exiting the program !

Answer 1

You can use kill(2) to send a signal to the process group. You can do this in the parent or any of the children.

int kill(pid_t pid, int sig);

If pid equals 0, then sig is sent to every process in the process group of the calling process.

For example:

kill(0, SIGTERM);

Answer 2

I think a better way to deal with this is to check for the quit command in the parent process before forking the child.

But if you want to do it in the child, you can send a signal to the parent.

kill(getppid(), SIGUSR1);

The parent process will need to establish a signal handler for SIGUSR1 that cleans everything up and exits. Or you could send a signal like SIGINT , whose default action is to kill the process, but it's better to implement a clean exit.

Also, in your code, you should check for the quit command before calling execvp . Otherwise, if there's a quit program in the user's path, it will never match your built-in quit , since execvp will succeed and not return.