/* File:  ~liux/public_html/courses/cop4610/examples/simple-cmd.cc
   Purpose: Demonstrate how to use fork, dup and exec system calls
            for I/O redictions, COP4610, FSU
   Author:  Xiuwen Liu
   On the web: 
    http://www.cs.fsu.edu/~liux/courses/cop4610/examples/simple-cmd-redirect.cc
   Compile:
     g++ -o simple-cmd-redirect simple-cmd-redirect.cc
*/
#include <sys/types.h>
#include <unistd.h>
#include <iostream.h>
#include <fstream.h>
#include <string.h>
#include <sys/wait.h>
#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/stat.h>

#define  MAX_ARG    50
int main(int argc, char *argv[])
{
  char fname[256];
  pid_t pid, child_pid;
  char  *my_argv[MAX_ARG];
  int status;
  int fd;
  if (argc < 2) {
    cerr << "Usage: " << argv[0]
	 << " command-to-run [redirect-in [redirect-out]] "
	 << endl;
    exit(-1);
  }
  /* The following is a standard pattern to use fork and exec
     to run new programs */
  
  pid = fork();
  if (pid == ((pid_t)-1)) {
    // Something must be wrong with the system if the program gets here
    perror("Fork failed: ");
    exit(-1);
  }
  else {
    /* Prepare command-line arguments */
    
    if (pid == 0) {
      // This is the child process
      cout << "Child-> This is the child process " << getpid()
	   << " whose parent is " << getppid() << endl;
      if (argc <= MAX_ARG) {
	cout << "Child-> I will start the following command: "<<endl;
	cout << "\t" << argv[1];
	my_argv[0] = argv[1];
	my_argv[1] = (char *)NULL;
	if (argc >= 3) {
	  /* Redirect the Input */
	  fd = open(argv[2], O_RDONLY);
	  if (fd < 0) {
	    cout << "Could not open file \"" << argv[2] << " input rediction."
		 <<endl;
	  }
	  else {
	    if (fd != 0) {
	      close(0); dup(fd); close(fd);
	    }
	  }
	}
	if (argc >= 4) {
	  /* Redirect the output */
	  fd = open(argv[3], O_WRONLY|O_CREAT|O_TRUNC);
	  if (fd < 0) {
	    cout << "Could not open file \"" << argv[3] << " output rediction."
		 <<endl;
	  }
	  else {
	    close(1); dup(fd); close(fd);
	  }
	}
	if (execvp(my_argv[0],my_argv)<0) {
          cerr << "Child-> Could not execute \""
               << my_argv[0] << "\".\n";
          perror("execvp");
          exit(-1);
        }
      }
      else {
	cerr << "Child-> Too many command-line arguments\n";
	exit(-1);
      }
    }
    else {
      // This is the parent process
      cout << "Parent-> This is the parent process " << getpid()
	   << " whose parent is " << getppid() << endl;
      cout << "I created a child whose id is " << pid << endl;
      child_pid = wait(&status);
      if (child_pid == pid) {
	if (WIFEXITED(status)) {
	  printf("Child %d terminated normally with status = %d.\n",
		 pid, WEXITSTATUS(status));
	}
	else {
	  if (WIFSIGNALED(status)) {
	    printf("Child %d terminated abnormally by signal %d.\n",
		   pid, WTERMSIG(status));
	  }
	  else {
	    if (WIFSTOPPED(status)) {
	      printf("Child %d stopped with signal %d.\n",
		     pid, WSTOPSIG(status));
	    }
	  }
	}
      }
      else {
	cerr << "Parent-> Something must be wrong. "
	     << child_pid << " and " << pid
	     << " should be identical.\n";
	exit(-2);
      }
    }
  }
  return 0;
}