Could someone help me add to the following C code to help with the following (code is below):

Command Execution - Once the shell understands what commands to execute it is time to implement the execution of simple commands. Since the execution of another program involves creating another process, you will have to use the fork() system call to create another process. Once you have created the new child process, that process must use the execvp() system call to execute the program. Finally, the parent (shell) process must wait for the child process to complete before releasing the childs resources using the waitpid() system call. However, the execvp() system call may return if there is an error. If it does, your shell should print an error, reset, and prompt for new input. Here is an example: prompt$ lalala -a Error: Command could not be executed prompt$

Built-ins - Not all commands are actually programs, and your shell must implement two built-in commands. In other words, if you encounter any of these two commands, do not execute them using fork(), exec(), and waitpid(). Instead, your shell should call a subroutine that implements the following functionality.:

exit terminates your running shell process and prints 'exit'. prompt$ exit exit (shell exits)

cd [PATH] Changes the present working directory. You will need to use the chdir() system call and update the PWD environmental variable with setenv(). prompt$ pwd /user/name/os/project1 prompt$ cd .. prompt$ pwd /user/name/os prompt$ cd project1 prompt$ pwd /usr/name/os/project1

showpid shows the last 5 child process IDs created by your shell. prompt$ showpid 4987 4992 5001 5002 5004

Better Prompt - Lets make your shell more usable. Modify the prompt so that it displays the current working directory before the $ sign: o /home/xkcd/$. Make the prompt a different color.

CODE:

#include

#include

#include

#include

#include

#define MAX_LINE 80

int main()

{

char str[100];

char *p;

char *args[MAX_LINE/2+1];

int count=0,pid,i;

printf("$ ");

fgets(str, 120, stdin);

while(strcmp(str, "exit ")!=0)

{

if(strcmp(str,"help ") == 0)

{

printf("enter Linux commands, or exit to exit ");

printf("$ ");

}

else

{

//fgets(str, 1000, stdin);

printf("$ ");

count=0;

//fgets(buff,sizeof(buff),stdin);

//eliminate /n in buff

str[strlen(str)-1]='\0';

//printf("%s ",buff);

//alocate memory for 10 array of strings

for(i = 0; i < 10; i++)

{

args[i] = (char*)malloc(20*sizeof(char));

}

//now make a argument list and add to string array

p=strtok(str," ");

strcpy(args[count++],p);

while(p!=NULL)

{

p = strtok(NULL," ");

if(p == NULL)

break;

strcpy(args[count++],p);

}

//after building list of commands , execute command using execvp , for that create child process

args[count]=NULL;

pid = fork();

if(strcmp(str,"exit") == 0)

{

exit(0);

}

if(pid == 0) //child process

{

//execvp(args[0],args);

if(strcmp(str,"help") == 0)

{

exit(0);

}

execvp(args[0],args);

perror("ps error: ");

printf("After execvp failed ");

exit(0);

}

else //parent process

{

//wait for chidl to finish

wait(0);

//printf("Finished executing user command %s ",buff);

if(strcmp(str,"exit") == 0)

{

exit(0);

}

str[0]='\0';

count=0;

*args=NULL;

}

}

fflush(stdin);

fgets(str, 1000, stdin);

}

}