Write a programl that creates two child processes: one to execute \'ls\' and the

ID: 3775460 • Letter: W

Question

Write a programl that creates two child processes: one to execute 'ls' and the other to execute 'sort'. After the forks, the original parent process waits for both child processes to finish before it terminates. The standard output of 'ls' process should be piped to the input to the 'sort' process. Make sure you close the unnecessary open files for the three processes. In C.

I have:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <unistd.h>
#include <fcntl.h>
/
int main()
{
   pid_t pid1,pid2;
   pid1 = fork();
   if(pid1 < 0)
   {
       /* an error occurred */
       perror("fork failed");
       exit(-1);
   }
   else if(pid1 == 0)
   {
       /* child process1 */
      system("ls > input.txt");
       return 0;
   }

else
{

       /* parent process */
       wait(&pid1);
       pid2 = fork();

       if(pid2 < 0)
      {
           perror("fork failed");
           exit(-1);
       }

       else if(pid2 == 0)
       {
           /* child process2 */
           system("sort -d input.txt");
           return 0;
       }

      else
       {
           /*Parent Process*/
           wait(&pid2);

           return 0;
       }
   }

return 0;
}

but i would like it to work with no system calls. Any ideas?

Explanation / Answer

for ls you can do this :

char *argument[2];

argument[0]="/bin/ls"; // first argument is the full path to executable i.e ls command

argument[1]=NULL; // list of arguments must be null terminated

Now replace the below statement using: execv

system("ls > input.txt");

replace to

execv(argument[0],argument);

Same way we can put a sort program in the bin directory and make it executable. say we created a sort file of sort.c and compile and place the sort in /bin .

so /bin/sort is accesible.If you place argument[0] to be

argument[0]="/bin/sort";

argument[1]=NULL; // list of arguments must be null terminated

execv(argument[0],argument);

Hope it helps. ls will work without no system calls but not sure about the sort. Most probably it will work.

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