# CSE 320 HW #3 Part II

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## Description

1 Introduction
The goal of this homework is to get your hands dirty with more C programming
but more importantly, to help you to familiarize yourself with such concepts as
creating new processes using fork(), using signals and how to block them, and
how to run programs using execve(). This homework consists of three parts.
In the second part, you need to implement a collection of three small programs to get you started and obtain some practice with concepts covered in this
homework.
2 Program I
This exercise will help you to get started with signal handlers and fork() function.
In the first program, you need to read a number N from the user through
the command line arguments and output the last digit on the Nth Fibonacci
number. Your application should parse the command line to get the number
N and create a child process using fork() function. The child process should
calculate the last digit of the Nth Fibonacci number and exit with the return
value equal to that last digit. The parent process should have a signal handler
installed to catch the SIGCHLD signal and once it gets the signal to reap the child
and print the final output by reading the exit status of the child. The program
should finish within one/few second(s) even for big values of N.
You should call the executable “fib” and we should be able to compile your
program by issuing the command “make fib”. Below you can find an example
of a sequence of commands that we will use to run your program:
\$ make fib
\$ ./fib 16
And this should print only “7” as it is the last digit of the 16th Fibonacci
number.
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3 Program II
This exercise will help to get started with execve() function.
In the second program, you need to implement a simple shell that prompts
a user for the command and tries to execute it unless the command is the
“exit” command. If it the “exit” command, then your program should stop its
execution. Otherwise, the program should try to execute the provided command
using execve() function. If it fails then the program should print “Failed to
execute CMD” where CMD should be substituted with the command that your
program failed to execute.
You should call the executable “simple shell” and we should be able to compile your program by issuing the command “make sshell”. Below you can find
an example of a sequence of commands that we will use to run your program
and an example of the possible execution:
\$ make sshell
\$ ./simple_shell
shell> ls -a
And this should have the same effect as typing “ls -a” in your terminal in
the same directory.
4 Program III
In the third part, you need to implement two programs. The first program
is a simple shell program called “shell” that needs to run the second program
called “child”. The shell program needs to ignore the SIGINT signal. It should
run the “child” program every time the user input “run” command in the shell
and then return back to the shell. To exit the program, the user should input
the “exit” command.
The second program called “child” should first block SIGINT signal and
then print numbers one through five inclusive with one-second interval and each
number being on a new line. After that, the SIGINT signal should be unblocked
and then the program should continue with printing numbers six through ten
inclusive with one-second interval and each number being on a new line. After
finishing printing, the “child” program should exit.
You should call the executables “shell” and “child”. We should be able to
compile your programs by issuing the command “make sigblock”. Below you
can find an example of a sequence of commands that we will use to run your
program:
\$ make sigblock
\$ ./shell
shell> run
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5 Note
No zombies. No memory leaks. No crashes.
6 Requirements
You need to follow the naming conventions and the asked way to implement
these exercises. If you are asked for some output then you need to print only
what was asked and nothing else.
7 Submission
In the third part of the homework, you will be provided with the link to create
the GitHub repository and specific instructions on how to submit this part of
this homework.
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