// test fork() and pipe()
//
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

int x = 0; // not shared with child

void error( const char *msg) { perror(msg); exit(1); }

int main( void) {

#ifndef PART1
  int fd[2]; if( pipe(fd) < 0) perror("pipe");
// 0 stdin
// 1 stdout
// fd[0] read side
// fd[1] write side
  dup2(fd[0],0); // connect stdin to pipe
  dup2(fd[1],1); // connect stdout to pipe
  close(fd[0]); close(fd[1]); // close unneeded descriptors
#endif

  int pid = fork(); if( pid < 0) error("fork");

  if( pid == 0) { // child

#ifdef PART1
    for( int i = 0; i < 5; ++i) { printf( "child %i %i\n", getpid(), ++x); sleep(1); }
    execlp( "ls", "ls", "-l", "Makefile", NULL);
    error("ls");
#else
    printf( "hi from child\n"); // goes into the pipe
    return 66;
#endif

  } else { // parent

#ifdef PART1
    for( int i = 0; i < 5; ++i) { printf( "parent %i %i\n", getpid(), ++x); sleep(2); }
#else
    char msg[BUFSIZ]; fgets(msg,BUFSIZ,stdin); // read from the pipe
    fprintf( stderr, "parent got: %s", msg); // write to terminal
    int s; // for child exit status
    wait(&s);
    fprintf( stderr, "s = %i, exit = %i\n", s, WEXITSTATUS(s) ); // write to terminal
#endif

  }
}