Assignment 1: Process API in Unix

Operating Systems COP4600
Assignment 1: Process API in Unix

Learning Objectives
The objective of this assignment is to experiment with process API in Unix and to better understand how
the Unix shell works by trying to mimic its behavior.
Problem 1
Write a C program that does the following:
• Takes an input from the command line. This input can be a sequence of characters without separators,
such as ”date” or ”ls”, or a sequence that contains separators (e.g., space or ”-”), such as ”ls -l”. Let’s
refer to this input as cmd if only one word, or cmd and params if more than one word. If the input
has multiple separators, cmd is the sequence of characters before the first separator, and params is
the rest of the input. For example, if the input is: ls -a -l then cmd is ’ls’ and params is ’-a -l’.
• Creates a new process (using fork());
• Makes the new process execute cmd with params as parameters, if given.
• Waits for the new process to finish executing, and then prints ++++ on a new line.
Problem 2
This problem builds significantly on the previous problem. Specifically, it asks you to again use fork() to
create processes and exec() (or one of the many variants) to assign the newly created processes what to do.
In addition, however, it asks you to mimic the behavior of a shell command such as:
ls | wc
What happens in the case above is the output of the first command (’ls’) becomes the input to the second
command (’wc’). (Try it in a terminal on a Unix machine). Thus, you are required to write another program
that:
• Expects an input of the form: cmd1 | cmd2
• Creates two processes
• Makes the first process run cmd1
• Makes the second process run cmd2
• Makes sure that the output of the first process becomes the input of the second process (using the
function pipe()).
• Waits for the two processes to finish before it ends by printing ++++ on a new line.
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Operating Systems COP4600, Spring 2021 Programming Assignment 1
What to Submit
Name your C files as problem1.c and problem2.c and place them in a folder called assignment1. Compress
the folder into a .tar file:
tar -cvf assignment1.tar assignment1
You will then need to download the tar file into your local machine. You may use FileZilla, PuTTY or
a similar tool. If doing it from the CLI, issue the following command: scp <usf
id>@cselxXX.csee.usf.edu:<abs path to the tar file> .
This will download the tar file to the location this command was run from. Submit the tar
file on Canvas.
Other Instructions and Suggestions
• This is an independent assignment. You are expected to work by yourself. If you use external sources
(such as code from the web), please cite them as comments in your code. We will use MOSS to
identify plagiarism in code.
• The C functions (that, in fact, use system calls) you’ll need include: fork(), wait(), pipe(), exec() (or
variants). You might want to also experiment with and use for debugging the functions getpid() and
getppid().
• For on-line reference manuals use the command man as below:
man -s 2 pipe
man man man
getppid
man -s 2 exec