17b.c

/*
============================================================================
Name : 17b
Author : Piyush Singh
Description : Write a program to execute ls -l | wc.
a. use dup
b. use dup2
c. use fcntl
Date: 19th Sep, 2025.
============================================================================
*/

// Version B: Use dup2() to redirect ls -l | wc
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

int main() 
{
    int pipefd[2];

    if (pipe(pipefd) == -1) 
    {
        perror("❌ Pipe creation failed");
        exit(1);
    }

    pid_t pid1 = fork();
    if (pid1 == 0) 
    {
        // Child 1: ls -l
        close(pipefd[0]); // Close read end
        dup2(pipefd[1], STDOUT_FILENO); // Redirect stdout to pipe
        close(pipefd[1]);

        execlp("ls", "ls", "-l", NULL);
        perror("❌ exec ls failed");
        exit(1);
    }

    pid_t pid2 = fork();
    if (pid2 == 0) 
    {
        // Child 2: wc
        close(pipefd[1]); // Close write end
        dup2(pipefd[0], STDIN_FILENO); // Redirect stdin to pipe
        close(pipefd[0]);

        execlp("wc", "wc", NULL);
        perror("❌ exec wc failed");
        exit(1);
    }

    // Parent closes both ends and waits
    close(pipefd[0]);
    close(pipefd[1]);
    wait(NULL);
    wait(NULL);

    return 0;
}

/*
Output:
╰─ ./17b                                                                      ─╯
       6      47     301
*/