/POSIX-Shell

A tiny UNIX shell.

Primary LanguageC

Tiny SHell - TSH

Description

  • A tiny UNIX shell supports only job control.
  • It's the 5th lab of 15-213: Introduction to Computer Systems.
  • Main routine is very simple, It (1): prints a prompt, (2): reads the command-line, (3): evaluate it.
  • Evaluation routine is also very simple, It:
    • (1): parses the command-line to build argv vector,
    • (2): checks if it's built-in command to execute it, if not, it forks a child and call execve to execute it,
    • (3): checks if the job is background or foreground,
      • (a): if it's bg; tsh doesn't wait for it to terminate.
      • (b): if it's fg; tsh waits for it to terminate and then reaps it.

How to use it?

  • Open your terminal and run the following:

    • git clone https://github.com/Alighorab/Tiny-Shell.git
    • cd Tiny-Shell
    • make
    • ./tsh

  • The following commands are supported:

    • quit: terminates the shell.
    • jobs: lists all background jobs.
    • bg <job>: restarts <job> by sending it a SIGCONT signal, and then runs it in the background. The <job> argument can be either a PID or a JID.
    • fg <job>: restarts <job> by sending it a SIGCONT signal, and then runs it in the foreground. The <job> argument can be either a PID or a JID.

  • You can also run your own programs by giving tsh the absolute path of your program.

    • For example:
      • tsh> /bin/ls -a
      • tsh> /bin/echo 'Hello world'
      • tsh> /bin/ps a

Hint 1: Programs such as more, less, vi, and emacs do strange things with the terminal settings. Don’t run these programs from your shell. Stick with simple text-based programs such as /bin/ls, /bin/ps, and /bin/echo.

Hint 2: tsh need not support pipes (|) or I/O redirection (< and >).

Lab Files

  • tsh.c: the main routine.
  • functionality.c: the main functionality of the shell, i.e., parsing and evaluating the command-line.
  • helpers.c: contains the job data structure and other helper functions to modify it.
  • handlers.c: contains signal handlers for the predicted signals: SIGTSTP, SIGINT, SIGTERM, and SIGCHLD.
  • ./tshref: the reference solution for the shell. (provided with the lab handout)
  • ./sdriver.pl: The trace-driven shell driver. Use the -h argument to find out how to use it.
  • traces/*: The 15 trace files that control the shell driver.
  • tests/*: programs to test on the shell.
  • shlab.pdf: lab writup.

The purpose of this lab

  • To become more familiar with the concepts of process control and signalling.