CS 3750: Operating Systems I

Fall 2020 - Lab 3

Due November 10, 2020

Turn in your source code and compiled executable programs, with the specified program names, to Lab 3 in the CS Homework system.

This is an individual assignment. All work must be your own. You should not look at any other student's work (in whole or in part, on paper or on screen), nor allow anyone else to look at yours, during the course of this assignment.

Implement a set of shell commands. Note that you must use the specified C library calls to implement the commands.

Implement your own versions of the shell commands listed below. Your version should simply have the basic, default behavior. You do not need to implement any of the command flags that are not specifically identified here.

The 'man' Unix shell command is your friend!

(ss stands for Stanislaus State)

• ls -l -a
  
  • Executable program name: ssls
  • System calls your program is allowed to use: execvp()
  • Notes: Your ssls program should print the same output as a standard Unix shell "ls -l -a" command would output.
• cat -n
  
  • Executable program name: sscat
  • System calls your program is allowed to use: fprintf(), open(), fgets(), and fclose(). Do not use: execvp() (or any other exec..()), system()
  • Notes: Remember to start the numbering of output lines at 1.
    For example, suppose you had a file, named myfile.txt, containing two lines, "hello" and "world". Then:
    

    prompt> ./sscat myfile.txt
    1: hello
    2: world
    

    (Remember, ./ just tells a shell to search in the current folder for a desired file. So the ./ above simply means that you have the executable sscat program located in your current folder.)
    If given more than one file on the command line, your sscat should output the contents of each file in turn. Do not restart the numbering between files. The number at the start of the final line in the final file should be a count of all the lines in all the files.
• grep
  
  • Executable program name: ssgrep
  • System calls your program is allowed to use: printf(), open(), fgets(), and fclose(), getline(), strstr(). Do not use: execvp() (or any other exec..()), system()
  • Notes: Your ssgrep program looks through a given file for a given search word. If the word is in the line, the line is printed to output. If the word is not in the line, the line is skipped. The search is case sensitive; if kitty is the search term a line containing Kitty will be skipped.
    If no command line arguments are given, or not enough, the program should exit gracefully.
    If the given file cannot be opened, the program should also exit gracefully.
    For example, suppose you had a file, named myfile.txt, containing the lines, "hello", "yellow", "Elevated" and "world". Then:
    

    prompt> ./ssgrep el myfile.txt
    hello
    yellow
    

The authors of our textbook have written a getting started programming C tutorial that may, indeed, help you get started.

Remember to test your programs on a variety of input. What happens when they are given invalid file names? Empty files? Not plain text files? Your programs should behave gracefully when given unexpected input.

Good commenting and code structure do, of course, count in the assignment grade.

Turn in your source code (3 .c files) and executables (3 files) to Lab 3 in the CS Homework system.