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

#define READ_END    0
#define WRITE_END   1

int main(int argc, char **argv) {
    int pid;
    int pipefd[2];

    // Create pipe and fds
    pipe(pipefd);

    pid = fork();
    if (pid == 0) {
        /* first child, gets write end of pipe */
        dup2(pipefd[WRITE_END], STDOUT_FILENO);
        close(pipefd[READ_END]);

        execlp( "/bin/ls", "ls", NULL );
    } else if (pid > 0) {
        /* parent, forks a second child */
        pid = fork();
        if (pid == 0) {
            /* second child, gets read end of pipe */
            dup2(pipefd[READ_END], STDIN_FILENO);
            close(pipefd[WRITE_END]);

            execlp("/usr/bin/less", "less", NULL);
        } else {
            /* parent, pipe fds must be closed so
               that 'less' gets an EOF */
            close(pipefd[READ_END]);
            close(pipefd[WRITE_END]);
            wait(NULL);
            wait(NULL);
        }
    }
}