OSAssignment2

Spawning Processes

Task

Create a C++ program, called OSShell, that will serve as a shell interface that accepts user commands, then executes each command in a separate process.

OSShell

• Create a shell interface (program that gives the user a prompt for a command)
  • Search the directories in the PATH environment variable and find the first executable with the name of the entered command
    • If one is found, spawn a new process to run that executable, and wait for its completion
    • If not found, print the following error message: ": Error running command"
  • Just hitting enter without typing a command should not print an error
  • After a command executes (or no command is found and error printed, or user simply hit enter), the shell interface should prompt the user for the next command
  • Also, on startup, your program should print a greeting along with instructions before providing the user with its first prompt
    • "Welcome to OSShell! Please enter your commands ('exit' to quit)."
• Implement 2 special commands (do not search for executable if either command is typed - do the following instead)
  • The first command is "history", which will show previous commands entered
    • Store up to the latest 128 commands
    • Print all recent commands (and their position)
  • The second command is "exit", which will terminate the shell
    • Your program should quit (no longer prompt the user for input)

Additional features

• If user input does not match a program in the PATH, check if it is a relative or full path to an executable file (NOT IMPLEMENTED)
  • If so, spawn a new process to run that executable, and wait for its completion
• Allow previous commands stored for the "history"command to persist between runs of OSShell
• Allow for an optional argument to the "history" command - an integer > 0 or the string 'clear'
  • If this parameter exists and is a positive integer, only print the most recent commands up to that number
    • Example: history 2 would print the two most recent commands
  • If this parameter exists and is the string 'clear', clear the history (and do not log the current history command in the history)
    • Example: history clear would clear the history list
  • Any number <= 0 or any non-integer other than the string 'clear' should result in an error
    • "Error: history expects an integer > 0 (or 'clear')"

Compile and Run

compile: make

run: ./bin/osshell