KuBash

This repository contains a Linux shell implemented in C which resembles the Bourne Again Shell

Run the shell

• Type the command make
• Type ./a.out to launch the shell
• Type exit or quit to exit the shell

Commands implemented

The following commands were coded for explicitly. All the other commands are supported by the shell using execvp()

pwd

• Returns the present working directory
• Code available in pwd.c and Header files in pwd.h

• Usage example

• Input: pwd
• Output: /home/kushagra/Documents/A2k20/OS/Assign2/KuBash

echo [args]

• Prints the contents in args on the shell
• Quotations preserve spaces, tabs and carriage returns
• Code available in echo.c and Header files in echo.h

• Usage example

• Input: echo "Operating Systems 2020"
• Output: Operating Systems 2020

cd [dir]

• Changes working directory to the directory given in dir
• If dir does not exist then error is flagged
• Both Relative and Absolute paths to the directory supported
• Path relative to cwd for the shell (called ~) is also implemented
• Code available in cd.c and Header files in cd.h

• Usage examples

• Input: kushagra@kushagra:~ cd ~
• Output: Prompt changes to kushagra@kushagra:~
• Input: kushagra@kushagra:~ cd ~/../../Assign2
• Output: Prompt changes to kushagra@kushagra:/home/kushagra/Documents/A2k20/OS/Assign2

ls [-a] [-l] [dir1] [dir2] [dir3]

• Shows the contents of the various directories given in the arguements
• -a flag implemented: Shows hidden files
• -l flag implemented: Shows details about each file
• Any permutation of the flags and directories is supported
• Code available in ls.c and Header files in ls.h

• Usage examples

• Input: ls -a ../exampledir
• Output: . .. prompt.c main.c
• Input: ls -la ../exampledir
• Output:
  drwxrwxr-x 3 kushagra kushagra 4096 Sep 09 11:28 .
drwxrwxr-x 6 kushagra kushagra 4096 Sep 09 11:50 ..
-rw-rw-r-- 1 kushagra kushagra 504 Sep 04 01:55 prompt.c
-rw-rw-r-- 1 kushagra kushagra 3865 Sep 09 01:39 main.c
  

pinfo [pid]

• Shows the process related information for a process
• If pid is not given as an arguement the pid of the shell is used as default
• Code available in pinfo.c and Header files in pinfo.h

• Usage examples

• Input: pinfo
• Output: pid -- 11403
Process Status -- R
Memory -- 2678784
Executable Path -- ~/a.out

history [count]

• Shows the last count number of commands written in the shell
• The history is stored using history.txt and stores not more than 20 commands
• If no arguement is given then last 10 commands are shown
• Code available in main.c

• Usage examples

• Input: history 3
• Output: cd ~
emacs &
history 3

setenv [var] [value]

• Allows the user to set the value of the environment variable [var] to [value]
• If value is omitted, the variable's value is set to the empty string
• Code available in set_env.c and Header files are in set_env.h

• Usage examples

• Input: setenv kush 100
• Ouput: On running env, kush=100 appears on the last line

unsetenv [var]

• Allows the user to uset the value of the environment variable [var]
• Code available in unset_env.c and Header files are in unset_env.h

• Usage examples

• Input: unsetenv kush
• Ouput: On running env, kush=100 is removed the last line

jobs

• Prints a list of all currently running background processes spawned by the shell in order of their creation times
• Prints job number,process ID and their state
• Code available in jobs.c and Header files are in jobs.h

• Usage examples

• Input: jobs
• Ouput: [1] Stopped emacs [8074]
[2] Running firefox [8101]

kjobs [job_num] [signal]

• Sends [signal] to the process with job number = [job_num]
• Code available in kjob.c and Header files are in kjob.h

• Usage examples

• Input: kjob 2 9
• Ouput: On running jobs we get [1] Stopped emacs [8074]
• As the signal=9 is SIGKILL and it killed the firefox background job

overkill

• Kills all background process at once
• Code available in overkill.c and Header files are in overkill.h

• Usage examples

• Input: overkill
• Ouput: On running jobs no output appears and all jobs are killed`

bg [job_num]

• Changes the state of a stopped background job to running (in the background).
• Code available in bg.c and Header files are in bg.h

• Usage examples

• Input: jobs
• Output: [1] Stopped emacs [8074]
[2] Running firefox [8101]
• Input: bg 1
• Input: jobs
• Output: [1] Running emacs [8074]
[2] Running firefox [8101]

fg [job_num]

• Brings the running or stopped background job corresponding to [job_num] to the foreground, and changes its state to running
• Code available in fg.c and Header files are in fg.h

• Usage examples

• Input: fg 1
• Output: Process comes to foreground waits for user to finish it

Background and Foreground processes

• If a command contains & as one of the arguements then it is considered a background process
• If a background process exits then the shell displays appropriate message using stderr
• The shell waits until a foreground process is finished

File Details

cd.c & cd.h

• Implement the cd command
• Code in cd.c and Header files are in cd.h

echo.c & echo.h

• Implement the echo command
• Code in echo.c and Header files are in echo.h

execute.c & execute.h

• Implement all the other commands which are not coded for explicitly
• Codes for background and foreground process handling
• Code in execute.c and Header files are in execute.h

headers.h

• Contains header files required throughout all the files
• Defines global variables

history.txt

• Stores last 20 commands written in the shell

ls.c & ls.h

• Implement the ls command
• Code in ls.c and Header files are in ls.h

main.c

• Implement the shell and receives user input
• Calls the corresponding command file based on user input

makefile

• Allows easy compilation of all the c files using a single command make

pinfo.c & pinfo.h

• Implement the pinfo command
• Code in pinfo.c and Header files are in pinfo.h

prompt.c & prompt.h

• Print the shell prompt kushagra@kushagra:[curdir]

pwd.c & pwd.h

• Implement the pwd command
• Code in pwd.c and Header files are in pwd.h