CyShell

Introduction

This is an implementation of a Linux shell written in C language Using Sys-Calls

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Run the shell

1. Clone this directory and cd into it.
2. Run the command make.
3. Run ./Shell to get a prompt of the form username@system_name:path.
4. Run any command in the shell. It can entail as many number of tabs and spaces, the shell accounts for those.
5. In order to exit, run quit or exit.

Features

Built-in commands implementation

These commands have been defined by me and are contained within the shell itself.

1. pwd

   • Displays the name of the working directory.
   • Implemented in pwd.c

2. ls [-l -a] [directory]

   • Lists all the files and directories in the specified directory in alphabetical order.
   • Variations such as ls, ls . , ls .. also work.
   • Also handles multiple directories as arguments. eg. ls -l dir1 dir2 dir3.
   • Throws error if you try to ls on anything except a directory.
   • Also highlights directories in blue and executable files in green.
   • Implemented in ls.c

3. cd [file]

   • Changes directory to the directory specified, throws an error if the directory does not exist.
   • Implemented in cd.c

4. echo [arguments]

   • Displays whatever is specified in [arguments]
   • Implemented in echo.c

5. history [num]

   • Prints the last arguement number of commands used in the shell (upto 20).
   • If no arguement is passed, by default it prints last 10 commands.
   • Retains the history even upon Shell exit - uses history.txt.
   • Implemented in history.c

6. pinfo [PID]

   • Prints the information about the id of the process passed as argument.
   • Information about PID ,Name , Memory , State and Executable Path are displayed.
   • By default argument value is set to id of the shell process.

7. jobs [-s -r]

   • Prints a list of all currently running and stopped jobs along with their pid in alphabetical order.
   • Gives the state of the job – Running or Stopped.
   • Jobs with status corresponding to the passed flag are displayed.
   • Implemented in jobs.c

8. fg <jobNumber>

   • Brings a running or a stopped background job with given job number to foreground.
   • Implemented in fg.c

9. bg <jobNumber>

   • Changes a stopped background job to a running background job.
   • Implemented in bg.c

10. sig [arguments]

    • Passes the provided signal to the given background process.
    • Implemented in signal.c

11. repeat [arguemnts]

    • Repeats the passed command given number of times.
    • Implemented in pipe.c

12. replay [arguments]

    • Executes a particular command in fixed time interval for a certain period.
    • Implemented in pipe.c

13. baywatch [arguements]

    • Interrupt: Print the number of times the CPU(s) has(ve) been interrupted by the keyboard controller.
    • Newborn: Prints the list of PIDs of active background processes in order of creation.
    • Dirty: Print the size of the part of the memory which is dirty .
    • Implemented in baywatch.c

Foreground and Background Processes

• To run a process in the background, follow the command with a '&' symbol. Eg. gedit &.
• Upon termination of a background process, the shell prints its PID and exit status.
• Handles & no matter where it is in the end. eg. gedit& , gedit &, ls -l&.

Additional Features

1. CTRL-Z

   • Changes the status of currently running job to stop, and pushes it to the background.

2. CTRL-C

   • Sends SIGINT signal to the current foreground job of the shell.
   • If there is no foreground job, then the signal does not have any effect.

3. CTRL-D

   • Logs you out of the shell without having any impact on the terminal.

4. Input-Output Redirection & Piping

   • Handles <, >, >>, and | operators appropriately, wherever they are in the command
   • Throws error if syntax is incorrect

Coding style

The code is completely modular with different .c files for each command, and a main.c binding them all together. Headers.h entails all the necessary header files, and global variables.