CODEWITHSUNDEEP
c
BigRedDog
BigRedDog

Reputation: 21

How to use execlp()?

How to do I make the second execlp("sort","sort,",(char *)0) output to the display?

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <sys/types.h>
#include <sys/stat.h>
#include "errno.h"

int main()
{
    int parprocID = getppid();//parent process id
    int c1Toc2[2];
    int c2Toc1[2];                            
    pipe(c1Toc2);//pipe 1, to child 2
    pipe(c2Toc1);//pipe 2, to child 1

    int cpid = 0;//child 1 pid
    int cpid2 = 0;//child 2 pid

    int child1,child2;//Child variable

    printf("Parent Process id is: %d.\n\n", parprocID);//parent pid introduction.

    child1 = fork();//creation of child 1
    if(child1 == 0)
    {
        cpid = getpid();
        printf("Child 1 created by process: %d has an id of %d.\n\n", parprocID, getpid());

        dup2(c1Toc2[1], STDOUT_FILENO);//redirect from stdout to pipe

        execlp("ls", "ls","-al","/bin", (char *)0);             

        exit(0);
    }
    else
    {
        child2=fork();  //creation of child 2   
        if(child2 == 0)
        {
            cpid2 = getpid();
            printf("Child 2 created by process: %d has an id of %d.\n", parprocID, getpid());

            dup2(c1Toc2[0], STDIN_FILENO);

            execlp("sort", "sort", (char *)0);
            exit(0);    
            close(c1Toc2[0]);
            close(c1Toc2[1]);   
        }
    }

    sleep(3);
    printf("PARENT: PROCESS waiting on children to complete\n");

    wait(NULL);
    wait(NULL);

    printf("Final print statement before exit\n");
    exit(0);
}

Child 1 has the execlps system call so the child 1 executes the ls program. dup2 redirects the output to the pipe. I think child 2 execlp sorts the ls but the code just hangs, I'm not sure if I'm doing it right, I'm expecting the child 2 to display what child 1 redirected. What comes next or where am I going wrong?

Upvotes: 2

Views: 603

Answers (1)

4566976
4566976

Reputation: 2499

The parent process and the child process 2 (sort) have open the writing end of the pipe too, thus sort is waiting for more input on its stdin: a close(c1Toc2[1]); before sleep(3); and before execlp("sort", "sort", (char *)0); must be added.

Upvotes: 1

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