Skip to content

Latest commit

 

History

History
110 lines (91 loc) · 5.04 KB

README.md

File metadata and controls

110 lines (91 loc) · 5.04 KB
Raw

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