#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <spawn.h>

#include <unistd.h>

#define USE_FORK
//#define USE_POPEN
//#define USE_POSIX_SPAWN
int some_var = 1;

int main(int argc, char** argv, char** env) {
    int pfds[2];
    int err;
    int pid;

    err = pipe(pfds);

#ifdef USE_FORK
    pid = fork();    
    if (pid < 0) {
        perror("fork");
        exit(EXIT_FAILURE);
    } else if (pid == 0) {
        // Child
        printf("Child: Some var: %d @ %p\n", some_var, &some_var);
        close(pfds[0]);
        close(STDOUT_FILENO);
        dup2(pfds[1], STDOUT_FILENO);

        some_var = 2;
        printf("Child: Some var: %d @ %p\n", some_var, &some_var);
        err = execv("/bin/date", argv);  
        perror("exec");
        exit(EXIT_FAILURE);
    } else {
        // Parent
        printf("Parent: Some var: %d @ %p\n", some_var, &some_var);
        close(pfds[1]);
        char buf[1024];
        int wstatus;
        FILE* fp = fdopen(pfds[0], "r");
        fgets(buf, sizeof(buf), fp);
        waitpid(pid, &wstatus, 0); 
        printf("FORK: Date returned: \"%s\" and exited with code %d\n", buf, wstatus);
        printf("Parent: Some var: %d @ %p\n", some_var, &some_var);
    }
#endif
#ifdef USE_POPEN
    FILE* fp = popen("/bin/date", "r");
    char buf[1024];
    int wstatus;
    fgets(buf, sizeof(buf), fp);
    wstatus = pclose(fp);
    printf("POPEN: Date returned: \"%s\" and exited with code %d\n", buf, wstatus);
    
#endif

#ifdef USE_POSIX_SPAWN
    int wstatus;
    posix_spawn_file_actions_t actions;
    posix_spawn_file_actions_init(&actions);
    posix_spawn_file_actions_adddup2(&actions, pfds[1], STDOUT_FILENO);
    posix_spawn_file_actions_addclose(&actions, pfds[0]);

    posix_spawn(&pid, "/bin/date", &actions, NULL, argv,  env);
    close(pfds[1]);

    char buf[1024];
    FILE* fp = fdopen(pfds[0], "r");
    fgets(buf, sizeof(buf), fp);
    waitpid(pid, &wstatus, 0); 
    printf("POSIX: Date returned: \"%s\" and exited with code %d\n", buf, wstatus);

#endif
    return 0;
}