/*
 * Assignment Four
 *
 * Write a program that:
 * A. Creates a child which waits for a command.
 * B. The child looks for the stdout redirection
 *    operator and if present redirects stdout,
 *    otherwise it just executes the program.
 * C. If the output file name does not exist,
      create the file.
 * D. The child terminates upon command completion
 *    (so the FDs will reset for the next cmd).
 * E. When a the EOF condition (^D) is detected,
 *    the parent and child programs terminate.
 *
 * Use the script program to show the program source code,
 * its compilation, and run time behavior.  Show BOTH
 * success and failure when executing the command.
 *
 * Here is a starting program that forks a child,
 * assumes the ls command is typed with the redirection
 * operator to a file called "lsout".
 *
 * Begin by testing this example with and without the
 * lsout file.  (Use "touch lsout" to create the file.)
 * You must add to this program:
 * A. The ability to run the program if the ">" feature
 *    was not used. (The user did not want I/O redirection.)
 * B. The ability to create a new file for output.
 * C. The ability to loop over multiple commands.
 * D. The ability to terminate on the ^D or EOF command.
 *
 */
#include <stdio.h>  /* Defines printf() and other fxxxxx() I/O services */
#include <stdlib.h> /* Defines exit() and other library support routines */
#include <unistd.h> /* Defines exec() family of services */
#include <string.h>
#include <fcntl.h>

char command[255] = "/bin/ls -l > lsout";

main (int argc, char *argv[], char *envp[])
{
  register char *cmdptr, **p;
  int pid, status;
  int fd1, fd3;

  for (p = argv; *p ; p++) {
    printf ("%s\n", *p);
  }
  if (!fork()) { /* Child code */
    printf ("Yo Dude...\n");
//    gets (command);
    printf ("%s\n", command);
    /* Char routines defined in /usr/include/string.h */
    cmdptr = strchr (command, '>');
    while (*(++cmdptr) == ' ') ;
    printf ("%s\n", cmdptr);
    /* Make sure your string is null terminated */
    /* O_XXXX bits defined in "man 2 open" */
    if ((fd3 = open (cmdptr, O_RDWR)) < 0) {
      printf ("Cannot open %s\n", cmdptr);
      goto error;
    } else printf ("Opened file \"%s\" with file descriptor %d\n",\
                    cmdptr, fd3);
    close (1);
    if ((fd1 = dup (fd3)) < 0) {
      /* Stream I/O defined in /usr/include/stdio.h */
      fprintf (stderr, "Duplicate failed\n");
      goto error;
    } else fprintf (stderr, "The new fd is %d\n", fd1);
    if (close (fd3) >= 0) {
      fprintf (stderr, "%s closed\n", cmdptr);
    } else { fprintf (stderr, "%s did not close\n", cmdptr);
error:
    printf ("%s: Cannot set up \"%s\" command\n", argv[0], command);
    exit (123);
    }
    /* Assume "/bin/ls -l" is to be executed */
    command[7] = 0;
    command[10] = 0;
    if (execl (command, command, &command[8], 0))
    /* -1 return means error */
    fprintf (stderr, "%s: Cannot find or access %s\n", argv[0], command);
    exit (0);

  } else { /* Parent code */
    pid = wait (&status);
    printf ("Statushigh = %d, Statuslow = %d, PID = %d\n",
         ((status & 0xff00) >> 8), (status & 0xff), pid);
    }
}