Project 1- Unix Shell

The next task is to modify the shell interface program so that it provides a history feature to allow a user to execute the most recent command by entering !!. For example, if a user enters the command ls l , she can then execute that command again by entering !! at the prompt. Any command executed in this fashion should be echoed on the user's screen, and the command should also be placed in the history buffer as the next command.

Your program should also manage basic error handling. If there is no recent command in the history, entering !! should result in a message No commands in history.

Can someone help me add the history feature to this code? The program is written in C on a Unix environment. I would really appreciate it. Thank you.

#include #include #include #include #include

#define MAX_LINE 80 /*The maximum length command*/

int main(void) { char *args[MAX_LINE/2+1];/*command line arguments*/ int should_run=1;/*flag todetermine when to exit program*/ while(should_run) { /*Shell promt*/ printf("osh>"); fflush(stdout); char command[MAX_LINE+1]; fgets(command, MAX_LINE+1 , stdin); // read and store command line input if (!strcmp(command,"exit")) should_run = 0; else { pid_t pid; pid = fork(); if (pid == 0) { command[strlen(command)-1] = 0; char *token = strtok(command, " "); int i = 0; while(token!=NULL) { args[i] = token; token = strtok(NULL, " "); i++; } args[i] = NULL; execvp(args[0], args); exit(0); } else { if (command[strlen(command)-2] == '&') continue; else wait(NULL); } } } return 0; }