Управление ресурсами в ВЧ 6

#include <fcntl.h>    /** fcntl  */
#include <stdio.h>    /** printf */
#include <unistd.h>   /** pipe   */
#include <assert.h>   /** assert */
#include <sys/wait.h> /** wait   */

#define PID_CHILD 0

// ls -al | wc -l && cat a.txt b.txt > c.txt.

int console; // FD консоли
int   input; // FD первого файла, выполняющего роль  STDIN_FILENO
int  output; // FD второго файла, выполняющего роль STDOUT_FILENO

void printFile(int fd) {
    lseek(fd, 0, SEEK_SET);

    char c;
    while (read(fd, &c, sizeof(char)) > 0) {
        write(console, &c, sizeof(char));
    }
    write(console, "\n", sizeof("\n"));
}

void moveData(int from, int to) {
    ftruncate(to, 0);
    lseek(from, 0, SEEK_SET);

    char c;
    while (read(from, &c, sizeof(char)) > 0) {
        write(to, &c, sizeof(char));
    }

    ftruncate(from, 0);
    lseek(to, 0, SEEK_SET);
}


int main() {
    console = open("/dev/tty", O_WRONLY);
    input   = open("/home/alex/CLionProjects/УВР/6/input.txt",  O_RDWR | O_TRUNC | O_CREAT);
    output  = open("/home/alex/CLionProjects/УВР/6/output.txt", O_RDWR | O_TRUNC | O_CREAT);

    assert(console != -1 && "Error: can't open console");
    assert(input   != -1 && "Error: can't open input.txt" );
    assert(output  != -1 && "Error: can't open output.txt");

    //close(STDOUT_FILENO);
    //fcntl(output, F_DUPFD, STDOUT_FILENO);
    dup2(output, STDOUT_FILENO);

    //close(STDIN_FILENO);
    //fcntl(input, F_DUPFD, STDIN_FILENO);
    dup2(input, STDIN_FILENO);

    /**
     * ls -al
     * Пишет в: output
     */
    int pid = fork();
    assert(pid != -1 && "Can't create new process");
    if (pid == PID_CHILD) {
        write(console, "Run command: ls /home -al\n", 26);
        execl("/bin/ls", "ls", "/home", "-al", NULL);
    }

    int status = 0;
    while ((wait(&status)) > 0) {};
    printFile(output);

    moveData(output, input);


    dup2(output, STDOUT_FILENO);
    dup2(input, STDIN_FILENO);

    /**
     * wc -l
     * Читает из  input
     * Пишет  в   output
     */
    pid = fork();
    assert(pid != -1 && "Can't create new process");
    if (pid == PID_CHILD) {
        write(console, "Run command: wc -l\n", 19);
        execl("/usr/bin/wc", "wc", "-l", NULL);
    }

    while ((wait(&status)) > 0) {};
    printFile(output);

    /**
     * cat a.txt
     * Читает из  input
     * Пишет  в   output
     */
    pid = fork();
    assert(pid != -1 && "Can't create new process");
    if (pid == PID_CHILD) {
        write(console, "Run command: cat a.txt b.txt\n", 23);
        execl("/bin/cat", "cat", "/home/alex/CLionProjects/УВР/6/a.txt", "/home/alex/CLionProjects/УВР/6/b.txt", NULL);
    }

    while ((wait(&status)) > 0) {};
    printFile(output);


    int c = open("/home/alex/CLionProjects/УВР/6/c.txt",  O_RDWR | O_TRUNC);
    moveData(output, c);


    return 0;
}