Computer Systems Engineering-1

Assignment 2

Jashn Arora 2018114006

my shell

Usage

Files

* shell.c    - contains the main functioning of the shell
* input.c    - contains the code for analysing the input
* shell.h     - contains all the required headers and functions
* display.c  - to display the prompt to user
* cd.c      - cd command
* pinfo.c   - pinfo command
* echo.c    - echo command
* pwd.c     - pwd command
* ls.c      - ls command
* fore_back_grnd.c   - handling background and foreground processes for commands which are executed through execvp
* parse_command.c - handles parsing of commands
* history.c - history command
* piping.c - handles piping
* redirection.c - handles redirection
* setenv.c - setenv command
* unsetenv.c - unsetenv command
* jobs.c - job command
* kjobs.c - kjob command
* fg.c - fg command
* bg.c - bg command
* overkill.c - overkill command
* cronjob.c - cronjob command

Functioning

* cd <directory path>       - Changes directory to the given path. Changes to shell home if no directory is provided
* pwd               - Shows the absolute path of the current working directory 
* echo              - Prints the message to the terminal. Handled single and double quotes.
* ls <al> <directory path>  - Handles all variations of ls with a and l flags and directory path
* pinfo <pid>           - Prints process related info (pid, Process Status {R, S, S+, Z}, memory and Executable Path) about given pid. Prints process related info of shell program if no pid is provided
* quit              - Exits the shell	
* history <n>           - Prints history of n (max 20) commands. Prints history of maximum 10 commands if n is not provided
* setenv var [value]   - creates the environment variable "var"
*                        sets its value to "value"
* unsetenv var          - unsets the value of the environment 
*                          variable "var"
* jobs                   - prints a list of all currently running jobs along with their job ids , pid, in particular,
                           background jobs, in order of their creation along with their state – Running or
                           Stopped.
* ​kjob <jobNumber> <signalNumber>  - takes the job id of a running job and sends a signal value to that process
* ​fg <jobNumber> ​        - brings a running or a stopped background job with given job number to foreground
* ​bg <jobNumber> ​        - changes a stopped background job to a running background
* ​overkill               - kills all background process at once
* quit ​                  - exits the shell
* CTRL-Z ​                - changes the status of currently running job to stop, and push it
                           in background process.
* CTRL-C ​                - causes a SIGINT signal to be sent to the current foreground job
                           of the shell​ . If there is no foreground job, then the signal has no effect.
* cronjob -c [command] -p <total time> -t <interval time>   -  runs the command( in [] ) 
*                                                               after every time interval for total time.
*  UP key recall         -  press the up key k no. of times and then press enter , the kth reccent command will display and run.  
                                                                                                                 
* All other commands are implemented using execvp
* Background Processing (can be run with '&') is handled for commands executed through execvp