Continuing after using execl() to start a script

[k3nt]

Hey,

So I have a shell script that I am calling with execl(). The script starts up 5 instances that are required by my c++ code and it has exit 0 at the end. How do I allow my program to continue on once it has called execl() and completed.

  if (pID == 0) {

        execl("/etc/init.d/test", "test", "start", NULL);
    }

Thank you!

[jsmith]

execl() never returns unless the system call fails. (ie, the program is not started).
You need to use fork() to create a child process and then run the execl() in the child.

If you want your program to continue executing while /etc/init.d/test is still running,
then there is nothing more to do -- just have the parent keep going.

If you want your program to pause while /etc/init.d/test is running and itself
continue only when test finishes, then you need to use waitpid() in the parent.

[bigearsbilly]

can you not use popen(3) ?

http://www.manpagez.com/man/3/popen/

or system?


you should describe what you are trying to do
rather than how you think it should be done.

[k3nt]

Thank you very much for the replies!

I have now realized a new problem. These instances that I am starting, are printing their status as they startup. Since I am putting these processes in the background, right now everything returns, and the code continues on. The problem is that my c++ relies on these instances being fully started, which is indicated by a certain sentence in their output. How would I go about reading the output from them and waiting until these key words are read, instead of just having the code sleep for a bit.

This is my current function...

int execute(const char *command)
{
    pid_t cpid;

    cpid = fork();

    switch (cpid) {
        case -1: perror("fork");
                 break; 

        case 0: execl("/etc/init.d/test", "test", command, NULL); /* this is the child */
                _exit (EXIT_FAILURE);

        default: waitpid(cpid, NULL, 0); 

    }

Thank you!

[jsmith]

You can redirect the output of the child process to your program, then have your program read and parse the data.