How to manage multiple pipes

Question

I'm trying to implement a multiple pipe for my shell in C. All I have is a pipe function that pipe `a | b` but not `a | b | c`. ``` int c[2]; int returnv; pid_t id; pipe(c); pid = fork()) == 0 if (pid) { dup2(c[1], 0); close(p[1]); close(p[1]); execvp(array(0), array); } if ((pid = fork()) == 0) { dup2(p[0], 1); close(p(0)); close(p[0]); returnv = execvp(array[0], array); } close(p[1]); wait(NULL); wait(NULL); wait(NULL); return returnv; ``` And this is a second version: ``` int i = 0; while (i < x) { pipe(c); if ((pid = fork()) == 0) { dup2(t[i], 1); if (i < 2) dup2(p[0], 1); close(p[1]); r = execvp(cmd[i][0], cmd[i]); } wait(NULL); close(p[0]); i += 1; t[i] = p[1]; ``` How can I make this code manage multiple pipes?

Accepted Answer

To perform multiples pipes you need to store all your commands somewhere.

That's why I used a tab of structure.

So first, you need a tab or something to store all your commands:

```
int main()
{
  char *ls[] = {"ls", NULL};
  char *grep[] = {"grep", "pipe", NULL};
  char *wc[] = {"wc", NULL};
  char **cmd[] = {ls, grep, wc, NULL};

loop_pipe(cmd);
  return (0);
}
```

Then the function will run through the tab and launch everything.

```
void    loop_pipe(char ***cmd) 
{
  int   p[2];
  pid_t pid;
  int   fd_in = 0;

while (*cmd != NULL)
    {
      pipe(p);
      if ((pid = fork()) == -1)
        {
          exit(EXIT_FAILURE);
        }
      else if (pid == 0)
        {
          dup2(fd_in, 0); //change the input according to the old one 
          if (*(cmd + 1) != NULL)
            dup2(p[1], 1);
          close(p[0]);
          execvp((*cmd)[0], *cmd);
          exit(EXIT_FAILURE);
        }
      else
        {
          wait(NULL);
          close(p[1]);
          fd_in = p[0]; //save the input for the next command
          cmd++;
        }
    }
}
```

How to manage multiple pipes

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