pipe_execl.c

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

enum {READ, WRITE};

int main()
{
    int fd[2];

    if (pipe(fd) == -1)
    {
        perror("Pipe");
        exit(1);
    }

    switch (fork())
    {
        case -1:
            perror("Fork");
            exit(2);

        case 0:
            // Child

            // The function fileno() examines the argument
            // stream and returns its integer descriptor.
            dup2(fd[WRITE], fileno(stdout));
            close(fd[READ]);
            close(fd[WRITE]);

            // int execl(const char *path, const char *arg0, ..., const char *argn, (char *)0);
            execl("/bin/ps", "ps", "-ef", (char *) 0);
            exit(3);

        default:
            // Parent

            dup2(fd[READ], fileno(stdin));
            close(fd[READ]);
            close(fd[WRITE]);

            execl("/usr/bin/wc", "wc", (char *) 0);
            exit(4);
    }

    return 0;
}