/* shell0.c - collect argv array from command line and execvp
 * 2009.09.24 Neal Nelson
 *
 * This version does not use strspn or strcspn, only strcpy.
 *
 * BUGS: This version has a memory leak because we malloc and do not free
 * each time through a shell command loop.
 *
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

#define MAXLINE 80
#define MAXWORDS 3

char *getArg(char *buf, char *word);
void *malloc();            /* should probably use calloc in general */

main()
{ char buf[MAXLINE];       /* fgets reads only MAXLINE-1 and adds zero */
  char word[MAXLINE+1];    /* add one for zero at end of line */
  char *argv[MAXWORDS+1];  /* make room for zero at end of argv array */
  char *p;
  int  i,argc;
  int  pid;

  /* Display argv for command lines until EOF (^d) at begin of line */
  printf("Entering new shell... enter ^d in first column to exit\n");
  while (fgets(buf, MAXLINE, stdin) != NULL)
  { /* fill up argv */
    p = buf;
    for (argc = 0; (p = getArg(p,word)) != NULL && argc < MAXWORDS; argc++)
    { printf(" >%s\n", word);
      argv[argc] = (char *)malloc(strlen(word) + 1);
      strcpy(argv[argc],word);                   /* an extra copy operation */
    }
    argv[argc] = (char *)0; /* Put NULL pointer to char at end of argv array */

    /* Print out argv */
    printf("The words in argv (max %d) ...\n",MAXWORDS);
    for (i = 0; i < argc; i++)
    { printf("%s\n",argv[i]);
    }

    /* Now fork a child to run the command */
    pid = fork();
    if (pid < 0)
    { perror("fork failed");
      exit(-1);
    }

    /* Child */
    else if (pid == 0)
    { printf("  Child Process\n");
      printf("  Executing %s command\n", argv[0]);
      printf("-----------------------------------------------------------\n");
      execvp(argv[0],&argv[0]);

      /* If execvp returns, the call has failed */
      perror("execvp failed to run");
      exit(-1);
    }

    /* Parent */
    else
    { wait( NULL );
      printf("-----------------------------------------------------------\n");
      printf("Parent Process\n");
      printf("--child has completed the %s command\n",argv[0]);
    }

  }
  printf("Leaving new shell...\n");
}

/* Copy next word after bufptr to word array (allocated by caller).
 * Return new bufptr or NULL if no word found
 */
char* getArg(char *bufptr, char *word)
{ char *p;
  int i;

  for (p = bufptr; isspace(*p); p++);              /* skip leading spaces */
  for (i = 0; !isspace(*p) && *p != '\0'; )        /* get next word */
  { word[i++] = *p++;
  }
  word[i] = '\0';
  return ( (i == 0) ? NULL : p ); /* if (i == 0) return NULL; else return p; */
}