ICS412 - Fall 2009 - Programming Assignment #2

ICS412 - Fall 2009 - Programming Assignment #2 -

Work alone
You are expected to do your own work on all homework assignments. You may (and are encouraged to) engage in general discussions with your classmates regarding the assignments, but specific details of a solution, including the solution itself, must always be your own work. (See the statement of Academic Dishonesty on the course's syllabus.)

What to turn in?
Turn in an archive (.zip, .tar, .tar.gz, .tgz, etc.) that contains:

A Makefile that generates all executables for all questions, and that must absolutely work without modification. Here is a sample Makefile, that you can use as a starting point.
All your source code, placed in files with reasonably intuitive names.

The archive must be turned in via e-mail to henric@hawaii.edu and to altunkay@hawaii.edu with a subject line like "ICS412: PA#2" before 11:59PM on the day the assignment is due.

In this assignment you'll implement ics412sh, a very simple UNIX Shell. Each question makes ics412sh a little bit closer to a real shell.

Question #1 (20 pts): ics412sh Version 1
Implement a Shell, ics412sh_v1, that prints a prompt to the screen, accepts a command typed by the user, executes that command, and prompts the use again. The Shell provides the three following built-in commands:

exit, logout: quits the Shell
cd: change the working directory (using the chdir() system call). If no parameter is passed, the directory is changed to the user's home directory, which is stored in the $HOME environment variable (See the getenv() standard C library function.)

The Shell also allows the user to run standard system programs (ls, cp, cat, sleep, etc.) When the user types a command, say, "ls", the Shell should look for it in "/bin", "/usr/bin". Looking for the existence of a file can be done with the stat() system call. The Shell then attempts to execute the command, printing an error message if it can't. Execution of the command is of course done via fork() and one of the exec() system calls.

Important: The Shell should print out error messages when the command doesn't exist, or when arguments to built-in commands are illegal. (System programs will deal with errors in their arguments themselves.)

Here is a transcript of an interaction with ics412sh_v1 (user input is in bold):

ics412sh% pwd /home/casanova/ics412/pa2 ics412sh% ls ics412sh_v1.c Makefile ics412sh% cd ics412sh% pwd /home/casanova ics412sh% cd .. ics412sh% pwd /home ics412sh% sleep 10 ^C ics412sh% logout

To get you started, and so that you don't struggle with commandline parsing, here is a starting point: ics412sh_skeleton.c. You can compile this program and run it. It doesn't execute the commands or handles the ^C, but it parses the commandline and prints out their arguments. Parsing is done via a single call to function parse_commandline(char *commandline, char ***args1, char ***args2, char **output), which is documented in the source code. (For this question, you do not need to worry about args2 or about output.)

Question #2 (5 pts): ics412sh Version 2
Implement a more evolved Shell, called ics412sh_v2, which extends the Shell from Question #1 as follows. The user must be able to stop the execution of a running system programs by hitting ^C. The Shell itself must not exit if the user types ^C. (Typing ^C sends a SIGINT signal to the process.)

Question #3 (10 pts): ics412sh Version 3
Implement a more evolved Shell, called ics412sh_v3, which extends the Shell from Question #2 by allowing the user to do pipes:

ics412sh% pwd /home/casanova/ics412/pa2 ics412sh% ls | grep ke Makefile ics412sh% exit

Function parse_commandline() will do the parsing of the commandline for you, and place the arguments to the second command in a NULL-terminated arrays (read the documentation of parse_commandline()).

Question #4 (10 pts): ics412sh Version 4
Implement a more evolved Shell, called ics412sh_v4, which extends the Shell from Question #3 by allowing the user to redirect output to a file:

ics412sh% ls > somefile ics412sh% ls | grep ke > someotherfile ics412sh% cat someotherfilels Makefile ics412sh% exit

Function parse_commandline() will do the parsing of the commandline for you, and place the name of the file to which output should be redirected in a string (read the documentation of parse_commandline()).

Question #5 (10 pts): ics412sh Version 5 [EXTRA CREDIT]
Implement a more evolved Shell, called ics412sh_v5, which extends the Shell from Question #4 by allowing the user to start jobs in the background, kill them, and wait for them:

ics412sh% ls -R / > foo & job [1] ics412sh% ls -R /home/ > foo2 & job [2] ics412sh% sleep 5 & job [3] ics412sh% sleep 10 [3] Done ics412sh% jobs [1] Running [2] Running ics412sh% kill 1 [1] Killed ics412sh% kill 3 No such job ics412sh% fg 2

henric@hawaii.edu