pid_t pid;
int err;

pid=fork();
if (pid == -1) 
    err=errno;
else if (pid == 0) {
    execv(arg0, rest_of_args);
    err = errno;  // should never get here
}
else
    waitpid(pid, &err, 0);

rc= execve ();
if (rc) {
    perror ("execve");
}

/*
Credit to Stephen Brennan (http://stephen-brennan.com/2015/01/16/write-a-shell-in-c/) for the split_line function.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>

#define LINESIZE 1024
#define RL_BUFSIZE 1024
#define TOK_BUFSIZE 64
#define TOK_DELIM " \t\r\n\a"

char **split_line(char *line)
{
    int bufsize = TOK_BUFSIZE, position = 0;
    char **tokens = malloc(bufsize * sizeof(char*));
    char *token, **tokens_backup;

    if (!tokens) {
        fprintf(stderr, "vsh: allocation error\n");
        exit(EXIT_FAILURE);
    }
		
    token = strtok(line, TOK_DELIM);
    while (token != NULL) {
        tokens[position] = token;
        position++;
	
        if (position >= bufsize) {
            bufsize += TOK_BUFSIZE;
            tokens_backup = tokens;
            tokens = realloc(tokens, bufsize * sizeof(char*));
            if (!tokens) {
		        free(tokens_backup);
                fprintf(stderr, "vsh: allocation error\n");
                exit(EXIT_FAILURE);
            }
        }
	
        token = strtok(NULL, TOK_DELIM);
     }
    tokens[position] = NULL;
    return tokens;
}
/*
int execute(char *command)
{
	system(command);
	
	return 1;
}
*/
int main(int argc, char **argv)
{
	char *cmd;
	int finish = 0;
	char *user = getenv("USER");
	char hostname[1024];
	char *pwd = getenv("PWD");
    char line[LINESIZE] = {0};
    char lineCopy[LINESIZE] = {0};
    char *command = NULL;
    char **args;
    
    // Print out a welcome message
    printf("Welcome to vsh\n");
	
	// Print out the message of the day
    system("/bin/cat /etc/motd");
    
    printf("\n");
	
	gethostname(hostname, 1024);
	
    while (!finish)
    {
		// Update 'pwd' variable
		pwd = getenv("PWD");
		// Print out prompt
		printf("[");
        printf(user);
        printf("@");
        printf(hostname);
        printf("] ");
        printf(pwd);
        printf(" $ ");
        fflush(stdout);
        
        if(NULL == fgets(line, sizeof line, stdin))
        {
			// If NULL, leave vsh
            finish = 1;
            printf("\nLeaving vsh\n");
        }
        else
        {
			// If there is something there...
            printf("The command read was s", line);
            printf("\n");
            char *newLine = strchr(line, '\n');
            
            if(newLine != NULL)
            {
                *newLine = '\0';
                strcpy(lineCopy, line);
            }
            
            command = strchr(line, ' ');
            
            if(command != NULL)
            {
                *command++ = '\0';
                printf("Command= _%s_\n\n", line);                
            }
            // Is the command pre-programmed into vsh?
            if(strcmp(line, "cd") == 0)
            {
				printf("Sorry, CD does not work in this version of vsh Shell. :(\n");
			}
            else if(strcmp(line,"programmer") == 0)
            {
                printf("The programmer of vsh is George Gibson\n");
            }
            else if(strcmp(line,"ver") == 0)
            {
                printf("The current version is 1.0\n");
            }
            else if(strcmp(line, "help") == 0)
            {
				printf("Help for vsh\n\nType a command to run it. The builtin commands are : cd, programmer, ver, help and exit.Their functions are as follows:\n\ncd: Change Directory. Changes the current working directory.\n\nprogrammer: Display the programmers of vsh.\n\nver: Display the version of vsh you are running.\n\nhelp: Launches this program.\n\nexit: Leave vsh Shell.\n\nThese are the only builtins in vsh, but note that if you define a command in /bin with one of these names, your program will not run in vsh unless you use it's explicit name (/bin/yourprogram) rather than \"yourprogram\". vsh 1.0 written and programmed by George Gibson.");
			}
            else if(strcmp(line,"exit") == 0)
			{
				finish = 1;
				printf("\nLeaving vsh\n");
			}
			else if(strcmp(line, "scroll") == 0)
            {
				// Easter egg
				printf(" _\n(@)\\__________  _\n|-|           \\(@)\n| |    VSH!    |-|\n|_|            | |\n(@)\\__________ |_|\n ~            \\(@)\n                ~\n\nWell done for finding the hidden easter egg in vsh!\n\n");
			}  
			// If command is not a vsh built-in, run the command
            else
            {
                args = split_line(line);
                pid_t pid;
				int err;

				pid=fork();
				if(pid == -1) 
					perror("vsh");
				else if(pid == 0) {
					execv(args[0], args);
					perror("vsh");  // Should never get here
				}
				else {
					waitpid(pid, &err, 0);
				}
            }
        }
    }
    
    return 0;
}