/* File:  ~liux/public_html/courses/cop4610/examples/simple-shell.cc
   Purpose: Demonstrate how to use fork and exec system calls to develop
            a simple shell
   Author:  Xiuwen Liu, 
   On the web: 
     http://www.cs.fsu.edu/~liux/courses/cop4610/examples/simple-shell.cc
   Compile:
     g++ -o simple-shell simple-shell.cc
*/

#include <sys/types.h>
#include <strings.h>
#include <string.h>

#include <sys/wait.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
#include <iostream.h>
#define  MAX_LINE   512
#define  MAX_ARG    50

extern char **environ;

int Parse_Command(char *buf, char *argv_list[]);

int main(void)
{
  char   buf[MAX_LINE];
  int    status;
  char   *my_argv[MAX_ARG];
  int    my_argc;
  int    i; 
  int    pid;
  do {
    printf("Next command -> "); /* Display prompt */
   
    buf[0]='\0';
    cin.getline(buf,MAX_LINE);
   
    if (buf[0] == '\0') continue;
    
    if (buf[strlen(buf)-1]=='\n') {
      buf[strlen(buf)-1]=0;
    }
    my_argc = Parse_Command(buf, my_argv);

    cout << "There are " <<  my_argc << " input arguments." << endl;
    for (i=0; i < my_argc; i++) {
      cout << "\t" << i+1 << "th = " << my_argv[i] << endl;
    } 
    
    if (my_argc == 0) continue;
    
    if (strcmp(my_argv[0],"myexit") ==0) break;
    if (strcmp(my_argv[0],"myenv")==0) {
      while(environ[i] != NULL) {
	cout << environ[i] << endl;
	i++;
      }
    }
    else {
      if ( (pid = fork()) < 0) {
	cerr << "Counld not create new process." << endl;
      }
      else {
	if (pid ==0) { /* Child */
	  cout << endl << "Child " << getpid() << " started\n";
	  if (execvp(my_argv[0],my_argv)<0) {
	    cerr << "Could not execute \""
		 << my_argv[0] << "\".\n";
	    perror("execvp");
	    exit(-1);
	  }
	}
	/* Parent */
	
	if((pid = waitpid(pid, &status, 0)) < 0) {
	  cout << "System call \"waitpid\" error.\n";
	}
	cout << "\nChild " 
	     << pid << " exited with status = " 
	     << status << ".\n";
      }
    }
  } while(1);
  return 0;
}

int Parse_Command(char *buf, char *argv_list[])
{
  int now_argc = 0;
  char *bufp;
  
  bufp = strtok(buf, " \t");
  argv_list[now_argc] = bufp;
  if (bufp == NULL) return now_argc;
  now_argc++; 
  while (bufp != NULL && now_argc < MAX_ARG) {
    bufp = strtok(NULL," \t");
    argv_list[now_argc++] = bufp;
  }
  now_argc --; /* Because the last one is an empty string */
  if (bufp != NULL) {
    cerr << "Argument list too long.\n";
  }
  return now_argc;
}