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C-Shell

Overview

C-Shell is a fully functional Linux shell that supports a wide range of functionalities, including semicolon-separated commands, piping, redirection, and all basic Linux commands. It can execute both foreground and background processes.

Features

Supported Commands

  • pwd: Prints the present working directory.
  • cd: Changes the directory based on the flags given.
    • cd, cd ., cd .., cd ~, cd <directory>
  • ls: Lists the contents of a particular directory based on the flags given.
    • ls, ls -a, ls -l, ls -al, ls -la, ls <directory>
  • echo: Prints a message on the terminal.
    • echo <"Hello World">
  • pinfo: Lists the details of a particular process (may be based on a process ID that is given).
    • pinfo, pinfo <pid>

Process Management

  • Foreground Processes: Processes that require the terminal to halt until their completion (e.g., vi, emacs).
  • Background Processes: Processes that run simultaneously without interrupting the terminal (e.g., emacs &).

Redirection and Piping

  • Input-output redirection: Redirects input or output to appropriate files (e.g., cat file1.txt > file2.txt, sort < sort.txt > sorted.txt).
  • Piping commands: Pipes two or more commands together (e.g., cat test.txt | grep a).
  • Piping with redirection: Combines piping and redirection (e.g., sort < sort.txt | grep a | wc > lines.txt).

Environment Variables

  • setenv: Sets new environment variables (e.g., setenv a 15).
  • unsetenv: Unsets an environment variable (e.g., unsetenv a).

Job Control

  • jobs: Prints all background jobs.
  • kjob: Sends a signal to a particular job number (e.g., kjob 1 9).
  • fg: Brings a running or a stopped background job with the given job number to the foreground (e.g., fg 1).
  • bg: Changes a stopped background job to a running background job (e.g., bg 1).
  • overkill: Kills all background processes at once.

Additional Features

  • Supports CTRL + C to interrupt processes.

Running the Shell

To run the shell, execute the following commands:

make
./a.out

Exiting From the shell

To exit from the shell, use the command

quit

Pseudo Home

The "Pseudo Home" directory for the shell is the directory in which the executable ./a.out resides. If the executable is being run from a different directory, specify the corresponding path.

Code Files and Functions

  • main.c:

    • prompt(): Prints the shell prompt.
    • loop(): Runs the main loop of the shell.
    • extract_command(): Extracts the command as an array.
    • piping(): Checks for piping in the command.
    • red_flag_check(): Checks for redirection flags.

  • pwd.c:

    • pwd(): Prints the present working directory.

  • ls.c:

    • Supports flags -a, -l, -la, -al. Can list contents of a specified directory.
    • ls_a(): Lists files and directories, including hidden files.
    • ls_l(): Lists detailed information about files and directories, excluding hidden files.
    • ls_al(): Lists detailed information about files and directories, including hidden files.
    • ls_basic(): Lists all files and directories.
    • ls_call(): Driver function to choose amongst the above functions.
    • flag_check(): Returns the correct flag given in the command.

  • cd.c:

    • cd(): Changes the directory based on the provided path.

  • echo.c:

    • echo_func(): Prints a string argument on the terminal.

  • pinfo.c:

    • pinfo(): Provides details about currently active/running processes.

  • foreground.c:

    • foreground(): Runs a child process in the foreground.

  • background.c:

    • background(): Runs a child process in the background.

  • history.c:

    • update_hist(): Adds a new command to the shell's history.
    • print_hist(): Prints the history of commands.

Note: Background processes for built-in commands are not supported.