vcsh

A basic shell in C

Installation Instructions

• Download the file as a zip or use the following command
  

$: git clone https://github.com/Vikr-182/vcsh 

• Inside the directory run
  

$: make
$: ./Shell

• To clean the object files, use
  

$ make clean

File stucture

.
├── builtins.h          # implements builtin commands like `cd`,`pwd`,`quit` and `echo`. 
├── cronjob.h           # implements `cronjob` command
├── direct.h            # contains the shell loop and initalisation as well as piping.
├── execute.h           # parses the string to check redirection and executes the command.
├── env.h               # implements `setenv` and `unsetenv`
├── history.h           # has history-related commands like `history` and for resizing.
├── input.h_            # takes the user input . It also checks if up arrow key was pressed or not.
├── jobs_commands.h     # implements functions like `fg`,`bg` and `kjob`.
├── jobs.h              # contains signal handlers for 'Ctrl+Z' and 'Ctrl+C' as well as 'SIGCHLD' handler. 
├                       # In addition, it contains updatejobs and showjobs which update and display the list respectively.
├── ls.h                # implements the `ls` command.
├── main.c              # contains the welcome message and call to the loop
├── nightswatch.h       # contains `nightswatch` implementation.
├── pinfo.h             # has `pinfo` implemented.
├── prompt.h            # displays the prompt.
├── global.h            # contains the variables shared across the files.

Commands implemented

-cd

• Changes directory using chdir
• Keeps a track of previous directory whenever changing to another directory to take care of cd -

-ls

• Implements ls -[la] in all different ways.
• If a directory is specified, the contents of that directory are obtained using readdir command which returns a struct which is passed as argument to stat function to obtain other information
• Appropriate color scheme is used for files, directories, links etc.

-pwd

• Uses the command getcwd .
• Error handling is done if size too big.

-echo

• First -n flag is looked whether to output the trailing newline.
• Across the traversal, $ is searched for to check presence of any environment variables.
• Also, string inside " " will be printed as it is. It is checked via keeping a start and end pointer for the opening and closing positions. If not closed, error is shown up.

-pinfo

• Only requires pid or null as argument. Error handling is done in case not done in such a way.
• All information regarding the process is obtained in various files located inside /proc/pid .

-nightswatch

• ncurses library is used to implement it/

-history <num>

• A file ".vcsh_history" keeps track of all commands typed.
• resize checks the number of commands entered till now. If it is greater than 25, the history file is resized by taking the most recent commands
• Prints the last num commands typed. If num not entered , prints the last 10 commands by default.

-setenv <variable> <value>

• Only accepts name of environment variable and value as input. Error handling is done otherwise.
• The variable is set using setenv command. If not able to set, error message shows up.

-unsetenv <variable>

• Takes only name of variable to be unset, error shown otherwise.
• Unset using unset command, error shown if not able to.

-fg <jobnumber>

• The process-id is retrieved using the procaarray.If no job number is specified, most recent process is taken into consideration.
• a SIGCONT signal is given to the process and the shell is made to wait for the child using waitpid. Ctrl+Z in the process is also handled.
• tcsetpgrp is used to give control to the child process.

-bg <jobnumber>

• The process-id is retrieved using the procaarray.
• SIGCONT is given to the the process using kill command.

-overkill

• Takes no arguments. Error shown otherwise.
• Iterates over the process array, keeps giving SIGINT signal until each one of them killed.

-kjob <jobnumber> <signalnumber>

• Takes input the job number and signal number. If no such job number exists or signal is invalid, error is thrown up.
• Identifes the process from job number through the procaarray list.

-jobs

• Prints the list of background jobs along with their status.
• Prints error if any argument given

-quit

• Will make the shell quit.

-cronjob -c <command> -t <time-period> -p <total-time>

• Takes input a single word command which will execute after time-period interval until total-time.
• Treated as background process.

Additional features implemented

• UP arrow key
• Use of '&' to put process in background
• Implementing piping and redirection .
• Ctrl+Z putting process in background
• Ctrl+C or any such signal ignored by parent process, only exits using quit command