Multiple pipes in C (Not complete, only for concept purpose)

pipex.c

/*
** pipex.c - multipipes support
*/

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>

/*
 * loop over commands by sharing
 * pipes.
 */
static void
pipeline(char ***cmd)
{
	int fd[2];
	pid_t pid;
	int fdd = 0;				/* Backup */

	while (*cmd != NULL) {
		pipe(fd);
		if ((pid = fork()) == -1) {
			perror("fork");
			exit(1);
		}
		else if (pid == 0) {
			dup2(fdd, 0);
			if (*(cmd + 1) != NULL) {
				dup2(fd[1], 1);
			}
			close(fd[0]);
			execvp((*cmd)[0], *cmd);
			exit(1);
		}
		else {
			wait(NULL); 		/* Collect childs */
			close(fd[1]);
			fdd = fd[0];
			cmd++;
		}
	}
}

/*
 * Compute multi-pipeline based
 * on a command list.
 */
int
main(int argc, char *argv[])
{
	char *ls[] = {"ls", "-al", NULL};
	char *rev[] = {"rev", NULL};
	char *nl[] = {"nl", NULL};
	char *cat[] = {"cat", "-e", NULL};
	char **cmd[] = {ls, rev, nl, cat, NULL};

	pipeline(cmd);
	return (0);
}

This is great example to understand multiple pipes , I was not clear with this concept but your code made me understand. Great work.

When I try to run the command cat /bin/ls | wc -l the program displays nothing and the gdb de-bugger shows the following error:
Program received signal SIGINT, Interrupt.
0x00007fffff0e45f1 in __libc_wait (stat_loc=0x0) at ../sysdeps/unix/sysv/linux/wait.c:29
29 ../sysdeps/unix/sysv/linux/wait.c: No such file or directory.

How to resolve this issue?

great work, well illustrated,,thanks alot

Great works but not complete work, it will fail to execute:
cat /dev/urandom | head -c 1000 | wc -c
because it wait for cat to finish, but head will finish first and stop cat

Having an array of String arrays is a really elegant solution to splitting up your commands. I didn't figure you could do something like that in C. Thank you for reminding me that i should be using collection of collections more often in any language. :)

I have a problem with your code when I execute a command like "time -p sleep 3 | echo toto". When I do it on the unix shell I get toto prited then 3 seconds after the time output. With your code the two outputs come after 3 seconds.

It's a very very very great example to understand multiple pipes

I think it has fd leak

this was great boy