HW #3 Part II Solution

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 pro-grams to get you started and obtain some practice with concepts covered in this homework.




Program I



This exercise will help you to get started with signal handlers and fork() func-tion.




In the rst 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 nal output by reading the exit status of the child. The program should nish within one/few second(s) even for big values of N.




You should call the executable \ b" and we should be able to compile your program by issuing the command \make b". Below you can nd 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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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 com-pile your program by issuing the command \make sshell". Below you can nd 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 e ect as typing \ls -a" in your terminal in the same directory.




Program III



This exercise will help you to get some experience with sigprocmask() function. In the third part, you need to implement two programs. The rst 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 rst block SIGINT signal and then print numbers one through ve 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 nishing 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 nd an example of a sequence of commands that we will use to run your program:




make sigblock



./shell shell run









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Note



No zombies. No memory leaks. No crashes.




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.




Submission



In the third part of the homework, you will be provided with the link to create the GitHub repository and speci c instructions on how to submit this part of this homework.
















































































































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