inter process communcation, parent - child

Hi there,

i have a problem with the ipc, i want to start a shell in the child process
like

Code:

//child
if (pid == 0){
       system("sh");
}
//parent
else{
        //readin from the command line (not the "sh" in child )
        //send read to child an execute it in the "sh"
}

the readline stuff is not the problem, but i dont know how i could switch between child and parent because the shell is running all the time, i just can enter the parent if i exit the shell, is there a way to switch the process after finishing a shell command ?

like:
child start sh
switch process
parent readin "command"
parent send "command" to child
child execute "command"
child send the result of the command back to parent
parent printf ....

Originally Posted by tallan

is there a way to switch the process

No. That's why it's called "inter process communication" and not "process switching".

Pretend the parent and the child are seperate programs. If you had two separate programs running at the same time and you wanted one to send a message to the other, how would you do that?

- you could write to and read from a file
- you could write to and read from a pipe
- you could write to and read from a socket

hope you understand my english correct, it isnt that good, with switch i mean i want to tell the child to sleep so the parent is working, like in

Code:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>

int main (){
   int pid, j, i;
   int pfds[2];
   pipe(pfds);
   char buf[30];

   int once = 0;
   pid = fork();



   if (pid == 0)
   {

      /* Kindprozess
       * wenn fork eine 0 zurückgibt, befinden wir uns im Kindprozess
       */
      for (j=0; j < 10; j++)
      {
    	  printf ("Kindprozess:  %d (PID: %d)\n", j, getpid());
    	  write(pfds[1], "test", 5);
        sleep (1);
      }
      exit (0);
   }
   else if (pid > 0)
   {
      /* Vaterprozess
       * Gibt fork einen Wert größer 0 zurück, so ist dies die PID des Kindprozesses
       */
      for (i=0; i < 10; i++)
      {
         printf ("Vaterprozess: %d (PID: %d)\n", i, getpid());
         read(pfds[0], buf, 5);
         printf("PARENT: read \"%s\"\n", buf);

         sleep (1);
      }
   }
   else
   {
      /* Wird ein negativer Wert zurückgegeben, ist ein Fehler aufgetreten */
      fprintf (stderr, "Error");
      exit (1);
   }
   return 0;
}

but with an running shell in the child
so i cant tell the shell to sleep to"switch"




so is there no way to do that without making a second programm ?

Have a look at "popen".

--
Mats

Originally Posted by tallan

so is there no way to do that without making a second programm ?

The point of fork() is that it is the same thing as a second program.

i have taken a look on "popen" but its the same problem i think or i dont get it....

i want to run a commandline programm in the child like sh, bash or sqlplus
and send commands from parent to the child witch base on the programm running on the child


example :

//child run sqlplus
//parent send sqlcommand to child
//child read the command
//child execute the command
//child send result to the parent
//parent read result

i really dont get it could someone plz give me an example ? sitting her for days but i dont find a way to "activate" the parent after starting sqlplus in the child...

so if there is anyone out there who know's the answer plz ..........