The purpose of this assignment is to use the fork, wait, and execvp to write a simple Linux shell. This shell is called MyShell, and the goal of MyShell is to continually prompt the user to supply a command, execute that command, and show the next prompt, once the command is executed. The file MyShell.c is already given to you. The file contains the functions shown in the below table. You should NOT change the method signatures. You should implement the missing portions of the program as per the guidelines given below, which is firmly required. You may add additional functions if necessary. int main(int argc, char** argv) The main function should display the MyShell> prompt. You should not change the name of the prompt. The main function should indefinitely run until terminated by CTRL+C or when the user types the exit command in the MyShell> prompt. It should call the parse() function in order to accept and process the command the user enters It should call the execute() function to actually execute the command char** parse(void) Gets the input typed by the user in the MyShell> prompt in the form of a line Splits the line into tokens The tokens are used to create a char** pointer which will serve as an argument for execvp int execute(char** args) char** args is obtained from the parse function You should fork a child and execute the command typed in by the user using EXECVP. You should only use execvp and not other versions. When fork fails, an error message should be printed. However, the next MyShell> prompt should be shown.

When execvp is not successful, an error message should be printed, and the child should terminate. However, the next MyShell> prompt should be shown. When an empty command is entered, the next MyShell> prompt should be shown. When the command exit is entered by the user, the main program must exit [You may or may not fork in order to implement the exit command]. The parent should wait for the child to terminate before it accepts another command. You can use wait or waitpid for this.

Other guidelines or useful hints: User command plus arguments will not exceed 255 characters Each command may have different number of arguments. We assume it will not exceed 255 arguments Variables stored in Stack cannot be accessed outside of a function/procedure, while data dynamically allocated in Heap can be accessed by any function within one program. Only one command should be typed at the MyShell> prompt, no pipelining of commands Commands run in MyShell> will assume the users original path: Type echo $PATH to see the current path variable setting. Myshell is not responsible for finding the path for the commands or files. If the user makes a mistake typing a command and/or its arguments, execvp should simply fail to run the command. A simple error should be shown, but next MyShell> prompt should be displayed. Please note that complicated commands like cd may not work as shown in the sample output. If execvp was not successful (e.g., a wrong command), remember to exit(0) the child process. The best command to test different cases is echo, for which you can give different numbers of characters and arguments.

Please comment code so I can learn.

Starter code

/** DONOT change the existing function definitions. You can add functions, if necessary. */ /** @brief Fork a child to execute the command using execvp. The parent should wait for the child to terminate @param args Null terminated list of arguments (including program). @return returns 1, to continue execution and 0 to terminate the MyShell prompt. */ int execute(char **args) { } /** @brief gets the input from the prompt and splits it into tokens. Prepares the arguments for execvp @return returns char** args to be used by execvp */ char** parse(void) { } /** @brief Main function should run infinitely until terminated manually using CTRL+C or typing in the exit command It should call the parse() and execute() functions @param argc Argument count. @param argv Argument vector. @return status code */ int main(int argc, char **argv) { return EXIT_SUCCESS; }

MyShell> MyShell> MyShell> pwd /media/sf_422Winter22/A1 MyShell> MyShell> MyShell> ls Makefile MyShell.c MyShell-Solution MyShell-Solution. c MyShell> MyShell> MyShell> cd error executing command: No such file or directory MyShell> MyShell> MyShell> cd .. error executing command: No such file or directory MyShell> MyShell> MyShell> hello my name is juhua error executing command: No such file or directory MyShell> MyShell> MyShell> wC MyShell. c 461481165 MyShell.c MyShell> MyShell> MyShell> grep - c the MyShell.c 6 MyShell> MyShell> MyShell> exit exitingroot@juhuah-VirtualBox:/media/sf_422Winter22/A1\# ./MyShell-Solution MyShell> MyShell>