The goal of this assignment is to construct a rudimentary implementation of a shell. This will require knowledge of everything that we've learned so far (string manipulation, memory model) as well as a solid understanding of a powerful Unix primitive: the process.
At its core, the shell is simply an overglorified infinite loop. On each iteration, it prints a prompt, reads a command (from stdin) and then carries out various actions based on the command received.
The prompt has been provided for you. You are allowed to change it, so long as the beginning of the prompt consists of the shell's PID surrounded by stache tags.
User input has also been taken care of for you. This is done using the getline() function. getline() is very powerful in that it is capable of reading in a buffer of arbitrary size and will allocate space accordingly. You have to make sure to free this space, however!
After input has been received, it must be tokenized on spaces so that you may effectively deal with the command.
There are two types of commands: builtins and non. Builtin commands are handled directly by the shell executable itself. Non-builtin commands must be handled by external executables.
You have been provided with shell.c which provides you with a rudimentary shell. It does not actually do anything other than loop and collect user input.
You should split up the functionality of your shell into various functions. Seriously. DO NOT WRITE YOUR ENTIRE SHELL IN THE shell() FUNCTION. Not only is this terrible practice, this project requires a lot of code and it will be far too easy to muck something up.
You do not need a header file in this assignment, although you certainly may provide one if you wish.
Builtins: You should implement echo, umask, backgrounding, cd and exit as builtins.
Non-builtins: Your shell should be able to execute any external executable via the execvp() command.
Piping: You should be able to handle an arbitrary amount of pipes.
Redirection: You should be able to handle the two basic types of redirection: > should redirect a process' stdout to a file, < should redirect a file to a process' stdin.
(Bonus) Globbing: Your shell should be able to handle basic globbing with the * operator. This is optional, but it would be really cool!
As usual, your assignment will be compiled and run through an automated test suite. Ensure that you don't mangle the prototype of the shell() function.