Project - Mini-Shell

Introduction:

Implement a minimalistic shell, mini-shell(msh) as part of the Linux Internal module. The objective is to understand and use the system calls w.r.t process creation, signal handling, process synchrnonization, exit status, text parsing etc..

Requirements list:

• Provide a prompt for the user to enter commands

  Display the default prompt as msh> Prompt should be customizable using environmental variable PS1

  • To change the prompt user will do PS1=NEW_PROMPT
  • Make sure that you do not allow whitespaces between = i.e., do not allow PS1 = NEW_PROMPT
  • In the above case, it should be treated like a normal command

• Execute the command entered by the user

  User will enter a command to execute If it is an external command

  • Create a child process and execute the command
  • Parent should wait for the child to complete
  • Only on completion, msh prompt should be displayed

Special Variables:

• Exit status of the last command (echo $?)

  After executing a command the exit status should be available echo $? should print the exit status of the last command executed

• PID of msh (echo $$)

  echo $$: should print msh's PID

• Shell name (echo $SHELL)

  echo $SHELL: should print msh executable path

Signal handling:

Provide short cuts to send signals to running program

Ctrl-C (Send SIGINT)

• On pressing Ctrl-C

  If a programming is running in foreground, send SIGINT to the progam (child process) If no foreground program exists, re-display the msh prompt

Built-in commands

• exit

  exit: This command will terminate the msh program

Design:

You should write down the how your are going to implement the project. You have to think through the design, then write down a detailed description of the design. Use diagram like flowchart to give clarity. Write down the algorithm/pseudo-code as appropriate.