Programming Assignment 1 CS450 

Programming Assignment 1
CS450 
1. This assignment is an individual effort. It is due on 02/08/2023
2. Requirements:
This programming assignment is inspired by one given at MIT
(https://pdos.csail.mit.edu/6.828/2012/homework/xv6-shell.html). The MIT assignment
asks the students to implement the pipe “|” and IO indirection “>” operators and
somewhat more in a very simple shell.
We ask you to implement the sequence command execution operator “;” and a program
execution command called “nonohup” and more. You should do this assignment by
modifying the skeleton code in the file called “programming assignment 1 (shell)”.
Invoke your shell from the shell that comes with xv6 or from a robust UNIX.
1) After your shell has started, it will give a prompt to the user. You should use
“$S23” for the prompt.
2) If the user types cmd1;cmd2 after the prompt, cmd1 will get executed,
followed by cmd2. After cmd2 is executed, your shell will give a new prompt in a
new line, ready to execute the next command line.
3) The commands cmd1 etc. are real commands supported by xv6 and they take
arguments. An example is the command echo “A”.
4) If the user types nonohup prog args, when the user hits return, the prompt
appears in a new line and the program prog and its arguments args will
execute in the background. We call it nonohup because it is different from the
POSIX command nohup. How is it the same and different?
5) Your shell shall support a command line with a string of 1 to 3 or more
commands connected by the “;” and nonohup operators. The commands and
nonohup will be executed from left to right. The string “cmd1;nonohup
prog;cmd2” will see cmd1 gets executed first. After it finishes, prog and
cmd2 execute in parallel. After cmd2 finishes, the prompt appears in a new line
even though prog may still being executed.
6) We ask you to write a program called whatIf. If invoked without an argument,
it will take input from what you type into the keyboard until you hit a
“ctrl+d.” If you give it a filename, it takes its input from that file.
As soon as whatIf is invoked, it forks a child process. Then both the parent and
the child will read from the same input, one line at a time. The parent will output
what it gets into a file called parent.txt one line at a time and the child’s
output goes to a file called child.txt one line at a tiem. After they are
finished with the input (from the keyboard or from the test file), they will exit
individually.
Run whatIf several times from your shell directly and from nononhup, and
describe what you observe, and postulate what may have happened. You can do
research to help you explain.
7) Hint: nonohup can be developed in two ways: As a built-in shell command; or
as a computer program. The second approach will result in a simpler shell but
may require you to use system calls like signal()that are not covered in your
text book nor by me.
3. Deliverables:
1) Source and executable objects with a README on how to build and execute
them.
2) A copy of the modified skeleton code, showing the modifications that you make
and with comments that explains how your code works.
3) A description and discussion on the behavior of the whatIf program. No more
than one page. Font size must be greater than 8.5.
4) The test data that you use and explanation on why the test data is of good
quality. If you use the equivalence partitioning method to generate your test
data, describe your equivalence partitions.
5) Show all test work and screenshots of test results in your report.
6) A manual page for nonohup including how it is different from nohup.
4. Install xv6 on your computer:
Programming Assignment 1 can be completed without using xv6. But starting on
Programming Assignment 2, you will be working with and making changes to xv6. We
recommend that you install xv6 on your computer before PA 2 is given, which will be
soon after your submission of PA 1. We recommend that you first install a virtualization
platform such as VMware so that your favorite OS can co-exist with xv6 in your
computer.