Assignment2writingaCommandInterpreter(Shell).pdf

Assignment 4 Writing a basic shell Due: September 8 Write a program in C to act as a command interpreter (Shell). The shell will give a prompt for the user to type in a command (from a set of commands), take the command, execute it, and then give the prompt back for the next command (i.e., actually give the functionality of a shell). Your program should do the following: ? Give a prompt shell for the user to type in a command ? Implement the following builtin commands: o cd dir : changes the directory to dir o pwd : prints the current directory o mkdir dir : creates a directory called dir o rmdir dir : removes the directory called dir o exit : exits the shell The commands are the same as the corresponding Linux commands by the same name. Do man to see the descriptions. You can use the standard system calls chdir, getcwd, mkdir, rmdir etc. to implement the calls (standard C library functions are available for these; look them up). These commands are called builtin commands since your shell program will have a function corresponding to each of these commands to execute them; no new process will be created to execute them. ? Any other command typed at the prompt should be executed as if it is the name of an executable file. For example, typing a.out should execute the file a.out . The file can be in the current directory or in any of the directories specified by the PATH environment variable. The file should be executed after creating a new process and then execing the file onto it. The parent process should wait for the file to finish execution and then go on to read the next command from the user. ? Should be able to redirect the output of a program to a file using and read the input of a program from a file using . For example, typing a.out outfile should send whatever was supposed to be displayed on the screen by a.out to the file outfile . Similarly, typing a.out infile should make a.out take the inputs from the file infile instead of the keyboard. ? Should be