Fork- transferring data from the child process to the parent process

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I want to pass the ls -la command from the child process to the parent process. I get an error. What am I doing wrong?

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

int main()
{
	pid_t pid;
	int fd[2];
	char buffer[3];
	char *argv[3]= {"ls", "-la", NULL};
	buffer[3] = *argv[1000];
	
	if(pipe(fd)<0)
		printf("Cannot create pipe\n");
	
	int pipe_result;
	pipe_result =pipe(fd);
	if (pipe_result<0)
		printf("error");
	
	pid= fork();
	
	if(pid<0) {
		printf("Couldn't create child process, err =%d\n", pid);
		return -1;
	} else if (pid ==0) {
		close(fd[0]);
		write(fd[1], buffer, 1000);
		close(fd[1]);
		
	} else {
		close(fd[1]);
		read(fd[0], buffer, 1000);
		close(fd[0]);
		}

	
	return 0;
	}

What I have tried:

I have no other ideas

Posted 28-Apr-21 11:39am

Rafał Kowalczyk 2021

Updated 28-Apr-21 20:13pm

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CPallini · Answer 1 · 2021-04-28T20:13:00

Try

C

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

const size_t BufSize = 1024;

int main()
{
  pid_t pid;
  int fd[2];

  char buffer[BufSize];

  const char * cmd = "ls -la";


  if(pipe(fd)<0)
    printf("Cannot create pipe\n");

  int pipe_result;
  pipe_result =pipe(fd);
  if (pipe_result<0)
    printf("error");

  pid= fork();

  if(pid<0) {
    printf("Couldn't create child process, err =%d\n", pid);
    return -1;
  } else if (pid ==0) {
    close(fd[0]);
    write(fd[1], cmd, strlen(cmd));
    close(fd[1]);

  } else
  {
    close(fd[1]);
    size_t nread = read(fd[0], buffer, BufSize);
    if (nread > 0)
    {
      for ( size_t n = 0; n < nread; ++n)
        putchar( buffer[n] );
      putchar('\n');
    }
    close(fd[0]);
  }
  return 0;
}