#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <string.h>

struct item {
    char *prog_name;
    int pid;
    struct item *next;
};

static int check_delimiter(char *arg)
{
    return !strncmp(arg, ";;", 3);
}

static void fill_in_item(char *arg, int pid, struct item **list)
{
    struct item *tmp_item = malloc(sizeof(struct item));
    tmp_item->pid = pid;
    tmp_item->prog_name = arg;
    tmp_item->next = *list;
    *list = tmp_item;
}

static void make_new_fork(int fd[2], char **begin_pos, struct item **list,
                          int *process_counter)
{
    static int first_process_flag = 0;
    int pid = fork();
    if(pid == -1) {
        perror("fork error");
        exit(1);
    }
    if(pid) {
        fill_in_item(*begin_pos, pid, list);
        ++*process_counter;
    } else {
        /* first process writes to pipeline */
        if(first_process_flag == 0) {
            close(fd[0]);
            dup2(fd[1], 1);
            close(fd[1]);
        /* second process reads */
        } else {
            close(fd[1]);
            dup2(fd[0], 0);
            close(fd[0]);
        }
        execvp(*begin_pos, begin_pos);
        perror(*begin_pos);
        exit(1);
    }
    ++first_process_flag;
}

static char* find_name_by_pid(int pid, struct item *list)
{
    while(list) {
        if(list->pid == pid)
            return list->prog_name;
        list = list->next;
    }
    return NULL;
}

static void clear_list(struct item *list)
{
    struct item *tmp;
    while(list) {
        tmp = list;
        list = list->next;
        free(tmp);
    }
}

int main(int argc, char **argv)
{
    int fd[2];
    int status, pid, process_counter;
    char **begin_pos, **end_pos;
    struct item *list = NULL;
    process_counter = 0;
    pipe(fd);
    if(argc == 1) {
        fprintf(stderr, "too few arguments\n");
        return 1;
    }
    ++argv;
    for(begin_pos = argv, end_pos = begin_pos + 1; *end_pos != NULL; ) {
        if(check_delimiter(*end_pos)) {
            *end_pos = NULL;
            make_new_fork(fd, begin_pos, &list, &process_counter);
            begin_pos = end_pos + 1;
            end_pos = begin_pos + 1;
        } else
            ++end_pos;
    }
    make_new_fork(fd, begin_pos, &list, &process_counter);
    close(fd[0]);
    close(fd[1]);
    for( ; process_counter; --process_counter) {
        pid = wait(&status);
        if(WIFEXITED(status) && WEXITSTATUS(status) == 0)
            printf("%s\n", find_name_by_pid(pid, list));
    }
    clear_list(list);
    return 0;
}